Western diet consumption impairs memory function via dysregulated hippocampus acetylcholine signaling

Western diet (WD) consumption during early life developmental periods is associated with impaired memory function, particularly for hippocampus (HPC)-dependent processes. We developed an early life WD rodent model associated with long-lasting HPC dysfunction to investigate the neurobiological mechanisms mediating these effects. Rats received either a cafeteria-style WD (ad libitum access to various high-fat/high-sugar foods; CAF) or standard healthy chow (CTL) during the juvenile and adolescent stages (postnatal days 26-56). Behavioral and metabolic assessments were performed both before and after a healthy diet intervention period beginning at early adulthood. Results revealed HPC-dependent contextual episodic memory impairments in CAF rats that persisted despite the healthy diet intervention. Given that dysregulated HPC acetylcholine (ACh) signaling is associated with memory impairments in humans and animal models, we examined protein markers of ACh tone in the dorsal HPC (HPCd) in CAF and CTL rats. Results revealed significantly lower protein levels of vesicular ACh transporter in the HPCd of CAF vs. CTL rats, indicating chronically reduced ACh tone. Using intensity-based ACh sensing fluorescent reporter (iAChSnFr) in vivo fiber photometry targeting the HPCd, we next revealed that ACh release during object-contextual novelty recognition was highly predictive of memory performance and was disrupted in CAF vs. CTL rats. Neuropharmacological results showed that alpha 7 nicotinic ACh receptor agonist infusion in the HPCd during training rescued memory deficits in CAF rats. Overall, these findings reveal a functional connection linking early life WD intake with long-lasting dysregulation of HPC ACh signaling, thereby identifying an underlying mechanism for WD-associated memory impairments.

24-h passive heat and cold exposures did not modify energy intake and appetite but strongly modify food reward

Effects of acute thermal exposures on appetite appear hypothetical in reason of very heterogeneous methodologies. The aim of this study was therefore to clearly define the effects of passive 24-h cold (16°C) and heat (32°C) exposures on appetitive responses compared to a thermo neutral condition (24°C). Twenty-three healthy, young, and active male participants realised three sessions (from 1 pm) in a laboratory conceived like an apartment dressed with the same outfit (Clo=1). Three meals composed of three or four cold or warm dishes were served ad libitum to assess energy intake (EI). Leeds Food Preference Questionnaires were used before each meal to assess food reward. Subjective appetite was regularly assessed and levels of appetitive hormones (acylated ghrelin, GLP-1, leptin, and PYY) were assessed before and after the last meal (lunch). Contrary to the literature, total EI was not modified by cold or heat exposure (p=0.120). Accordingly, hunger scores (p=0.554) were not altered. Levels of acylated ghrelin and leptin were marginally higher during the 16 (p=0.032) and 32°C (p<0.023) sessions, respectively. Interestingly, implicit wanting for cold and low-fat foods at 32°C and for warm and high-fat foods at 16°C were increased during the whole exposure (p < 0.024). Moreover, cold entrées were more consumed at 32 °C (p<0.062) and warm main dishes more consumed at 16°C (p<0.025). Thus, passive cold and hot exposures had limited effects on appetite and it seems that offering some choice based on food temperature may help individuals to express their specific food preferences and maintain EI.

Response inhibition training as an intervention to modify liking and wanting for foods based on energy density: a proof of concept study

The ubiquity of energy-dense, processed foods has been implicated as a salient feature of the modern 'obesogenic' environment. Cognitive strategies, such as response inhibition training, have been demonstrated to reduce the hedonic value of such foods in previous studies. However, this effect has generally been inconsistent or heterogenous, depending on the outcome measure, characteristics of the sample, and the specificity of food stimuli. Characterising the extent of generalised effects may help define the application of this type of intervention in natural settings. A repeated-measures, proof-of-concept study, using mobile app-based response inhibition training (RIT) versus a control app-based activity (N = 25), was undertaken to establish the valid application of a food reward measure to assess intervention efficacy. Liking (i.e., affect) and wanting (i.e., motivation) for food stimuli categorised by energy density were taken concurrently pre- and post-training. A statistically significant reduction in explicit liking, but not implicit wanting, for foods irrespective of their energy density was observed during the RIT app-based training session relative to the control (p = .041, ηp2 = .16). However, effect sizes associated with devaluation of energy-dense relative to low calorie food stimuli, although non-significant, were higher when measured as implicitly wanting (p = .098, ηp2 = .11) than explicit liking (p = .756, ηp2 = .00). Trends in explicit stimulus evaluations were empirically discordant from implicit evaluations for low calorie foods in particular. Additional research is needed to investigate whether these trends are reproducible with larger samples, trained and novel food stimuli in outcome measures, and more comprehensive training protocols.

Evidence that carbohydrate-to-fat ratio and taste, but not energy density or NOVA level of processing, are determinants of food liking and food reward

This virtual (online) study tested the common but largely untested assumptions that food energy density, level of processing (NOVA categories), and carbohydrate-to-fat (CF) ratio are key determinants of food reward. Individual participants (224 women and men, mean age 35 y, 53% with healthy weight, 43% with overweight or obesity) were randomised to one of three, within-subjects, study arms: energy density (32 foods), or level of processing (24 foods), or CF ratio (24 foods). They rated the foods for taste pleasantness (liking), desire to eat (food reward), and sweetness, saltiness, and flavour intensity (for analysis averaged as taste intensity). Against our hypotheses, there was not a positive relationship between liking or food reward and either energy density or level of processing. As hypothesised, foods combining more equal energy amounts of carbohydrate and fat (combo foods), and foods tasting more intense, scored higher on both liking and food reward. Further results were that CF ratio, taste intensity, and food fibre content (negatively), independent of energy density, accounted for 56% and 43% of the variance in liking and food reward, respectively. We interpret the results for CF ratio and fibre in terms of food energy-to-satiety ratio (ESR), where ESR for combo foods is high, and ESR for high-fibre foods is low. We suggest that the metric of ESR should be considered when designing future studies of effects of food composition on food reward, preference, and intake.

Paradoxical effects of feeding status on food consumption and learning performance in zebrafish (Danio rerio)

Associative learning is often studied using food reward as the unconditioned stimulus (US). With warm-blooded species, to get the subject more motivated the solution has been to feed less, making the subject hungrier. Here we show the opposite with zebrafish. We randomly assigned zebrafish to two groups: a once-a-day-fed and a five-times-a-day-fed group, with the same amount of food fed per occasion for fish of both groups, a feeding regimen that lasted for three months. Subsequently, we trained fish by pairing food (US) with a red cue card (the conditioned stimulus, CS), which were placed together in one arm of a plus-maze across eight training sessions. We also ran unpaired training, in which the CS and US were presented in different arms. We found the previously once-a-day-fed zebrafish to consume less food throughout habituation and training sessions compared to the previously five-times-a-day-fed ones. Furthermore, five-times-a-day-fed fish in the paired group swam significantly closer to the CS during a post-training probe trial compared to the five-times-a-day-fed unpaired fish, a paired training effect that was absent in once-a-day-fed fish. Groups did not differ in health or general activity. In sum, elevated chronic feeding improved food consumption and enhanced learning and memory performance without affecting activity levels in adult zebrafish.

Effects of pre-exercise high and low glycaemic index meals on substrate metabolism and appetite in middle-aged women

Few studies have examined the influence of pre-exercise meals with different glycaemic indices (GIs) on substrate oxidation and non-homeostatic appetite (i.e. food reward) in adults of various ages and ethnicities. We aimed to examine the effects of pre-exercise high and low GI meals on substrate oxidation and food reward in middle-aged Japanese women. This randomised crossover trial included fifteen middle-aged women (aged 40⋅9 ± 6⋅5 years, mean ± sd). The participants consumed a high or low GI breakfast at 09.00 and rested until 11.00. Thereafter, participants performed a 60-min walk at 50 % of their estimated maximum oxygen uptake (11.00-12.00) and rested until 13.00. Expired gas samples were collected every 30 min prior to walking, and samples were collected continuously throughout the walking and post-walking periods. Blood samples and subjective appetite ratings were collected every 30 min, except during walking. The Leeds Food Preference Questionnaire in Japanese (LFPQ-J) was used to assess food reward at 09.00, 10.00, and 13.00 h. The cumulative fat oxidation during exercise was higher in the low GI trial than in the high GI trial (P = 0⋅03). The cumulative carbohydrate oxidation during walking was lower in the low GI trial than in the high GI trial (P = 0⋅01). Trial-by-time interactions were not found for any food-reward parameters between trials. Low GI meals elicited enhanced fat oxidation during a subsequent 60-min walk in middle-aged women. However, meals with different GIs did not affect food reward evaluated over time in the present study.

Neural correlates of appetite in adolescents

Appetitive characteristics are associated with child adiposity, but their biological underpinnings are unclear. We sought to investigate the neural correlates of psychometric and behavioral measures of appetitive characteristics in youth. Adolescents (14-18y; 39F, 37M) varying in familial obesity risk and body weight (20% with overweight, 24% with obesity) viewed pictures of high energy-density (ED) foods, low-ED foods and non-foods during fMRI scanning on two separate days. On one day participants consumed a 474 ml preload of water (0 kcal, fasted) and on another (counter-balanced) 474 ml milkshake (480 kcal, fed), before scanning. A multi-item ad libitum meal (ALM) followed scanning. Parents completed Child Eating Behavior Questionnaire (CEBQ) sub-scales assessing food approach and food self-regulation. Caloric compensation was calculated as the percentage of preload intake compensated for by down-regulation of ALM intake in the fed vs. fasted condition. Analyses correcting for multiple comparisons demonstrated that, for the fasted condition, higher CEBQ Food Responsiveness scores were associated with greater activation to high-ED (vs. low-ED) foods in regions implicated in food reward (insula, rolandic operculum, putamen). In addition, higher caloric compensation was associated with greater fed vs. fasted activations in response to foods (vs. non-foods) in thalamus and supramarginal gyrus. Uncorrected analyses provided further support for associations of different measures of appetitive characteristics with brain responses to food cues in each condition. Measures of appetitive characteristics demonstrated overlapping and distinct associations with patterns of brain activation elicited by food cues in fasted and fed states. Understanding the neural basis of appetitive characteristics could aid development of biobehaviorally-informed obesity interventions.

No effect of prefrontal transcranial direct current stimulation (tDCS) on food craving, food reward and subjective appetite in females displaying mild-to-moderate binge-type behaviour

Previous work suggests there may be an effect of transcranial direct current stimulation (tDCS) on appetite control in people at risk of overconsumption, however findings are inconsistent. This study aimed to further understand the potential eating behaviour trait-dependent effect of tDCS, specifically in those with binge-type behaviour. Seventeen females (23 ± 7 years, 25.4 ± 3.8 kg m-2) with mild-to-moderate binge eating behaviour completed two sessions of double-blind, randomised and counterbalanced anodal and sham tDCS applied over the right dorsolateral prefrontal cortex at 2.0 mA for 20 min. Subjective appetite visual analogue scales (VAS), the Food Craving Questionnaire-State (FCQ-S), and Leeds Food Preference Questionnaire (LFPQ) were completed pre- and post-tDCS. Participants then consumed a fixed-energy meal, followed by the VAS, FCQ-S and LFPQ. No difference between pre- and post-tDCS scores were found across fullness (p = 0.275, BF10 = 0.040), prospective consumption (p = 0.127, BF10 = 0.063), desire to eat (p = 0.247, BF10 = 0.054) or FCQ-S measures (p = 0.918, BF10 = 0.040) when comparing active and sham protocols. Only explicit liking and wanting for high-fat sweet foods were significantly different between conditions, with increased scores following active tDCS. When controlling for baseline hunger, the significant differences were removed (p = 0.138 to 0.161, BF10 = 0.810 to 1.074). The present data does not support the eating behaviour trait dependency of tDCS in a specific cohort of female participants with mild-to-moderate binge eating scores, and results align with those from individuals with healthy trait scores. This suggests participants with sub-clinical binge eating behaviour do not respond to tDCS. Future work should further explore effects in clinical and sub-clinical populations displaying susceptibility to overconsumption and weight gain.

The energy content of meals with a similar macronutrient distribution may have a greater impact on appetite sensations than food preferences in adolescents with obesity: A secondary analysis

PURPOSE

The energy and macronutrient composition of a meal has been shown to influence postprandial appetitive responses, but it is not clear how energy content independent of macronutrient distribution affects postprandial appetite in adolescents with obesity. Extracting data from a primary study testing the effect of energy turnover on appetite, this secondary analysis assessed how fixed meals varying in energy content with similar macronutrient distributions influences postprandial appetite sensations and food reward.

METHODS

Using a randomised, counterbalanced crossover design, N = 14 adolescents with obesity (Mage = 12.71, SDage = 0.99; 10 female) consumed fixed lunch meals with similar macronutrient content starting at 750 kcal in energy and progressively increasing by 250 kcal on three different test days. Liking and wanting for food images varying in fat and taste were assessed at baseline and immediately after meal consumption. Appetite sensations were assessed in half-hour intervals from baseline to 1-h post-meal.

RESULTS

The area under the curve for subjective hunger (p < .001, ω = 0.36), desire to eat (p < .001, ω = 0.54), and prospective food consumption (p = .004, ω = 0.32) were significantly lower after consumption of the higher calorie meals relative to the lowest. Explicit wanting for sweet foods increased after intake of the intermediate calorie meal yet decreased after the highest calorie meal (p = .014, ω = 0.09). Conversely, implicit wanting sweet bias increased after consumption of the test meal independent of energy content (p < .001, ω = 0.15).

CONCLUSION

The consumption of additional calories without a meaningful change in macronutrient distribution may affect appetite sensations more reliably than hedonic responses to energy-dense foods in adolescents with obesity.

Pavlovian-instrumental transfer effects in individuals with binge eating

BACKGROUND

The food addiction model of binge-eating postulates that hyperpalatable food can sensitize the reward processing system and lead to elevated cue-elicited motivational biases towards food, which eventually become habitual and compulsive. However, previous research on food reward conditioning in individuals with binge-eating is scarce. The present study examined the Pavlovian-instrumental transfer (PIT) effects in individuals with recurrent binge-eating. It was hypothesized that hyperpalatable food would elicit specific transfer effects, i.e., biased responding for the signaled food even after satiation on that food, and this effect would be stronger in individuals with binge-eating compared to healthy controls.

METHODS

Fifty-one adults with recurrent binge-eating and 50 weight-matched healthy controls (mean age: 23.95 [SD = 5.62]; % female = 76.2%) completed the PIT paradigm with food rewards. Participants also completed measures of hunger, mood, impulsivity, response disinhibition, and working memory. Mixed ANOVAs were conducted to examine transfer effects and if they differed between individuals with binge-eating and those without.

RESULTS

The group by cue interaction effect was not significant, suggesting that the specific transfer effect did not differ between groups. The main effect of cue was significant, indicating that the outcome-specific cue biased instrumental responding towards the signaled hyperpalatable food. However, the biased instrumental responding was attributable to suppressed responding in the presence of the cue predicting no reward, rather than enhanced responding in the presence of the specific food-predicting cues.

CONCLUSIONS

The present findings did not support the hypothesis that individuals with binge-eating would be more vulnerable to specific transfer effects elicited by hyperpalatable food, as measured by the PIT paradigm.

Development, sensitivity and reliability of a French version of the Leeds Food Preference Questionnaire (LFPQ-fr) for the evaluation of food preferences and reward

BACKGROUND

. There is a growing global interest in the evaluation of food reward, necessitating the adaptation of culturally appropriate instruments for use in empirical studies. This work presents the development and validation of a culturally adapted French version of the Leeds Food Preference Questionnaire (LFPQ-fr).

METHODS

. The LFPQ-fr was developed and validated in healthy-weight adults using the following systematic approach: i) selection and validation of appropriate food pictures; ii) linguistic translation of liking and wanting constructs in the target population (n=430; 81% female; 42.2 ± 12.7 years); iii) validation of the sensitivity and reliability of the task performed in a fasted state and in response to a standardized test meal (n=50; 50% female; 30.0 ± 8.4 years).

RESULTS

. During the first and second phases, the nutritional and perceptual validation of culturally appropriate food pictures and pertinent reward constructs, respectively, was demonstrated in a healthy-weight French sample. Findings from the third phase indicated that all food reward components were sensitive to the test meal and showed moderate to high agreement in both fasted (Lin's CCC =.72-.94) and fed (Lin's CCC = .53-.80) appetitive states between visit 1 (V1) and visit (V2). Except for explicit liking fat bias, all primary outcomes were statistically consistent in fasted and fed states between V1 and V2. Changes in fat and taste biases in response to a standardized meal for all primary outcomes were also consistent between V1 and V2 except for explicit liking fat bias (Lin's CCC = .49- .72).

CONCLUSION

. The LFPQ-fr developed and tested in this study is a reproducible and reliable method to assess food reward in both the fasted and fed states in a healthy-weight French population.

Effect of transcranial direct current stimulation on homeostatic and hedonic appetite control and mood states in women presenting premenstrual syndrome across menstrual cycle phases

PURPOSE

This study investigated the acute effect of anodal transcranial direct current stimulation (a-tDCS) over the left dorsolateral prefrontal cortex (DLPFC) on appetite, energy intake, food preferences, and mood states in the luteal and follicular phases of the menstrual cycle in women presenting premenstrual syndrome.

METHODS

Sixteen women (26.5 ± 5.2 years; 1.63 ± 0.1 m; 64.2 ± 12.8 kg; body mass index 24.0 ± 5.0 kg/m²; body fat 27.6 ± 7.5%) with the eumenorrheic menstrual cycle were submitted to a-tDCS and sham-tDCS conditions over their follicular and luteal phases. At pre - and post-tDCS, hunger and desire to eat something tasty, (analogic visual scale), the profile of mood states (POMS), and the psychological components of food preferences (Leeds Food Preference Questionnaire-BR) were assessed. Participants recorded their food intake for the rest of the day using a diary log.

RESULTS

There was a trend towards main effect of condition for decreased implicit wanting for low-fat savory food after a-tDCS but not sham-tDCS regardless of menstrual cycle phase (p = 0.062). There was no effect for self-reported hunger, desire to eat, energy and macronutrient intake, and on other components of food preferences (explicit liking and wanting for low- and high-fat savory and sweet foods, implicit wanting for low- and high-fat sweet and high-fat savory food); as well as for mood states.

CONCLUSIONS

Although no significant effects of a-tDCS were found, the present investigation provides relevant perspectives for future studies.

Impact of exercise timing on perceived appetite and food reward in early and late chronotypes: An exploratory study in a male Saudi sample

There is very limited evidence on the influence of diurnal exercise timing on appetite control, and none on food reward or how an individual's chronotype could moderate such effects. We examined the impact of acute exercise timing on perceived appetite and food reward in young Saudi adults with early or late chronotypes. Forty-five young adults (23 ± 4 years; BMI = 25.1 ± 4.0 kg/m²) completed the Morningness-Eveningness Questionnaire (MEQ) and were divided into early (score = 59 ± 5) or late (score = 41 ± 6) chronotypes. Participants attended the laboratory after ≥4 h fast on two occasions for an AM (8:00-10:00) and PM (17:00-19:00) 30-min moderate-intensity cycling bout in a randomized counterbalanced order. Appetite ratings and food reward (Arab Leeds Food Preference Questionnaire) were measured before and after exercise. An acute exercise-induced decrease in hunger was found, which appeared to be dependent upon diurnal timing and chronotype, with hunger being more suppressed after AM exercise in the early chronotypes and after PM exercise in the late chronotypes. There was greater wanting for low-fat sweet foods after AM exercise relative to PM exercise, whereas there was greater wanting for high-fat sweet food and sweet relative to savoury food after PM exercise compared to AM exercise. These preliminary findings suggest that diurnal timing of exercise impacts food preferences, and that chronotype may influence the appetite response to an exercise bout at different times of day.

Non-invasive vagus nerve stimulation in a hungry state decreases heart rate variability

Vagus nerve signals from the gut to brain carry information about nutrients and drive food reward. Such signals are disrupted by consuming large amounts of high-calorie foods, necessitating greater food intake to elicit a similar neural response. Non-invasive vagus nerve stimulation (nVNS) via a branch innervating the ear is a candidate treatment for obesity in humans. There is disagreement on the optimal location of nVNS in the ear for experimental and clinical studies. There are also no studies comparing nVNS in hungry and post-prandial states. We aimed to compare ear position(s) for nVNS and explore the effects of nVNS during hungry and post-prandial states on proxies for autonomic outflow (heart-rate variability) and efferent metabolism (gastric wave frequency and resting energy expenditure). In a within-subject design, 14 participants (10 women, on average 29.4 +/- 6.7 years old) received nVNS in four different locations (cymba conchae, tragus, earlobe, or tragus AND cymba conchae) on separate days. In each session, participants were asked to consume a palatable chocolate flavored milk. With electrography on the abdomen and indirect calorimetry in a canopy, we measured electro-cardiogram, electro-gastrogram and resting energy expenditure for 15 min before and at least 35 min after consumption of the palatable drink. We also collected ratings of the palatable drink and internal and other states. Pre-drink consumption (in a hungry state) we observed no differences in the effect of location of acute nVNS on resting energy expenditure and gastric wave measures. However, nVNS in cymba conchae decreases heart-rate variability (relative to sham) and ratings of how much participants want to consume the drink (relative to tragus AND cymba conchae and a trend relative to sham). After drink consumption and with continued nVNS, gastric wave frequency is unchanged, and resting energy expenditure increases regardless of stimulation location. Heart-rate variability decreases in all locations, except cymba conchae. We also observe a trend for an increase in gastric wave amplitude in late post-drink consumption time-points in cymba conchae. We observe no support for the combined stimulation of tragus AND cymba conchae being more effective than either of the individual locations. These results suggest that nVNS in the cymba conchae in a hungry state has a similar acute effect on vagal tone as food consumption: to decrease heart rate variability. This effect then negates the usual postprandial effects of a decrease in heart rate variability as seen in the other nVNS locations. These preliminary observations suggest that nVNS in cymba conchae may act primarily on vagal afferent autonomic (and only modestly on metabolic output) in a similar way as food consumption does.

Early resource scarcity alters motivation for natural rewards in a sex- and reinforcer-dependent manner

RATIONALE

Early life adversity impacts reward-related behaviors, including reward seeking for drugs of abuse. However, the effects of early stress on natural rewards, such as food and social rewards, which have strong implications for symptoms of psychiatric conditions such as major depressive disorder (MDD), are understudied. To fill this gap, we used the limited bedding and nesting (LBN) procedure to assess the impact of early resource scarcity on motivational drive for both food and social rewards in rats.

METHODS

Male and female Long Evans rats were reared in either an LBN environment, with limited nesting materials and no enrichment, from their postnatal day 2-9 or control environment with ample nesting materials and enrichment. As adults, they were tested for reward-seeking behavior on progressive ratio operant tasks: food reward (sucrose) or social reward (access to a same-sex/age conspecific).

RESULTS

We observed sex differences in the impact of LBN on motivation for natural rewards. In males, LBN increased motivation for both a sucrose and social reward. In females, LBN reduced motivation for sucrose but had no effect on social reward.

CONCLUSIONS

These results suggest that the effects of LBN on motivation for natural rewards are both sex- and reinforcer-dependent, with males and females showing differential motivation for food and social rewards following early scarcity. Our previous data revealed an LBN-driven reduction in motivation for morphine in males and no effect in females, highlighting the reinforcer-dependent impact of early resource scarcity on motivated behavior more widely.

Chronic experience with unpredictable food availability promotes food reward, overeating, and weight gain in a novel animal model of food insecurity

Ubiquitous, easy access to food is thought to promote obesity in the modern environment. However, people coping with food insecurity have limited, unpredictable food access and are also prone to obesity. Causal factors linking food insecurity and obesity are not understood. In this study we describe an animal model to investigate biopsychological impacts of the chronic unpredictability inherent in food insecurity. Female rats were maintained on a 'secure' schedule of highly predictable 4x/day feedings of uniform size, or an 'insecure' schedule delivering the same total food over time but frequently unpredictable regarding how much, if any, food would arrive at each scheduled feeding. Subgroups of secure and insecure rats were fed ordinary chow or high-fat/high-sugar (HFHS) chow to identify separate and combined effects of insecurity and diet quality. Insecure chow-fed rats, relative to secure chow-fed rats, were hyperactive and consumed more when provided a palatable liquid diet. Insecure HFHS-fed rats additionally had higher progressive ratio breakpoints for sucrose, increased meal size, and subsequently gained more weight during 8 days of ad libitum HFHS access. Insecurity appeared to maintain a heightened attraction to palatable food that habituated in rats with secure HFHS access. In a second experiment, rats fed ordinary chow on the insecure schedule subsequently gained more weight when provided ad libitum chow, showing that prior insecurity per se promoted short-term weight gain in the absence of HFHS food. We propose this to be a potentially useful animal model for mechanistic research on biopsychological impacts of insecurity, demonstrating that chronic food uncertainty is a factor promoting obesity.

Challenges and new opportunities for detecting endogenous opioid peptides in reward

The endogenous opioid peptide system, comprised of enkephalins, endorphins, dynorphins, and nociceptin, is a highly complex neurobiological system. Opioid peptides are derived from four precursor molecules and undergo several processing events yielding over 20 unique opioid peptides. This diversity together with low in vivo concentration and complex processing and release dynamics has challenged research into each peptide's unique function. Despite the subsequent challenges in detecting and quantifying opioid peptides in vivo, researchers have pioneered several techniques to directly or indirectly assay the roles of opioid peptides during behavioral manipulations. In this review, we describe the limitations of the traditional techniques used to study the role of endogenous opioid peptides in food and drug reward and bring focus to the wealth of new techniques to measure endogenous opioid peptides in reward processing.

Suboptimal Weight Loss 13 Years After Roux-en-Y Gastric Bypass: Is Hedonic Hunger, Eating Behaviour and Food Reward to Blame?

Purpose

Suboptimal weight loss (SWL) and weight regain (WR) following bariatric surgery are common. The exact reasons for this phenomenon remain to be fully elucidated. To compare hedonic hunger, food preferences, food reward and eating behaviour traits between participants with SWL and optimal weight loss (OWL) 13 years after Roux-en-Y gastric bypass (RYGB).

Materials and Method

Cross-sectional case control study where participants experiencing SWL or OWL (< or ≥ 50% of excess weight, respectively) post-RYGB were compared to a non-surgical control group matched for pre-operative body mass index. Hedonic hunger (Power of Food Scale), implicit and explicit liking and wanting for high-fat and low-fat savoury and sweet food (Leeds Food Preference Questionnaire) and eating behaviour (Dutch Eating Behavior Questionnaire, Three-Factor Eating Questionnaire and the Food Cravings Questionnaires State and Trait-reduced) were assessed.

Results

In total, 75 participants were recruited from the bariatric surgery observation study (BAROBS). Disinhibition, hunger, emotional, external and restrained eating, frequency of cravings and hedonic hunger were lower in the OWL, compared with the SWL and/or control groups. Implicit wanting and explicit liking and wanting for high-fat savoury and high-fat sweet food were lower, and implicit wanting for low-fat savoury food higher, in the OWL, compared with the SWL and/or control groups.

Conclusion

SWL 13 years after RYGB is associated with dysfunctional eating behaviours, increased preference and reward for high-fat food and increased hedonic hunger. Future longitudinal studies are needed to establish the cause-effect relationship between these variables.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11695-022-06075-z.

Appetite Changes in Weight Regain and Weight Maintenance After Roux-en-Y Gastric Bypass

PURPOSE

Roux-en-Y gastric bypass (RYGB) surgery produces significant weight loss. However, a number of patients experience weight regain years after surgery. Factors driving weight regain after surgical interventions are currently being explored. Our objective was to investigate appetite-related measures associated with weight regain after RYGB surgery.

MATERIALS AND METHODS

Using a cross-sectional design, 29 participants (49.6 ± 9.1 years of age; current BMI 32.4 ± 4.7 kg/m², 43.6 ± 8.9 months post-RYGB) were stratified into tertiles according to weight regain per month after nadir (weight maintenance (WM), n = 9; low weight regain (LWR), n = 10; and high weight regain (HWR), n = 10). The average weight regain was, by design, significantly different between the groups (WM = 2.2 ± 2.5 kg; LWR = 10.0 ± 3.4 kg; HWR = 14.9 ± 6.3 kg regained, p < 0.05). Appetite (visual analog scales), olfactory performance ("sniffin sticks"), eating behaviors (Three Factor Eating Questionnaire), food reward (Leeds Food Preference Questionnaire), and appetite-related hormones (ghrelin, PYY, GLP-1 and leptin) were measured fasting and in response to a standardized test meal.

RESULTS

Dietary restraint was significantly higher than clinical cutoffs in WM and LWR (p < 0.05). As expected, significant time effects were noted for ghrelin, PYY, and GLP-1, but there were no group differences.

CONCLUSION

The results suggest that appetite-related outcomes are similar across individuals who have maintained weight loss and experienced regain following RYGB.

Motivation to consume palatable foods as a predictor of body image dissatisfaction: Using the Power of Food Scale in a Brazilian sample

The Power of Food Scale (PFS) is a questionnaire for self-assessing the motivation to consume palatable foods, especially in environments where food is abundant and constantly available. This study aimed to a) assess the factorial structure of the PFS in a Brazilian sample and b) examine the relationship between the power of food and body image dissatisfaction and BMI. The PFS and Body Shape Questionnaire (BSQ) were applied to a sample of 300 adults. Data were analysed using confirmatory factor analysis. Composite reliability (CR) was used to verify factor reliability. A partial least squares structural equation model was used to verify the effect of the PFS score on body image dissatisfaction. The PFS had an adequate factorial structure in this Brazilian sample, showing three well-defined factors: food available (CR = 0.91), food tasted (CR = 0.84), and food present (CR = 0.87). The BSQ showed one reliable factor (CR = 0.97). The power of the food aggregate factor significantly predicted body mass index (β = 0.16; p = .01) and body image dissatisfaction (β = 0.46; p < .001). The effect size was small for body mass index (f² = 0.02) and medium for body image dissatisfaction (f² = 0.26). The food present factor also had a slightly higher average among the three PFS factors. Women had higher PFS scores than men. Understanding the role that this motivation plays in physical and psychological outcomes such as body dissatisfaction can contribute to developing treatment strategies and support health professionals' performance in clinical settings.

Effects of Glucagon-like peptide 1 (GLP-1) analogs in the hippocampus

The glucagon-like peptide-1 (GLP-1) is a pleiotropic hormone very well known for its incretin effect in the glucose-dependent stimulation of insulin secretion. However, GLP-1 is also produced in the brain, and it displays critical roles in neuroprotection by activating the GLP-1 receptor signaling pathways. GLP-1 enhances learning and memory in the hippocampus, promotes neurogenesis, decreases inflammation and apoptosis, modulates reward behavior, and reduces food intake. Its pharmacokinetics have been improved to enhance the peptide's half-life, enhancing exposure and time of action. The GLP-1 agonists are successfully in clinical use for the treatment of type-2 diabetes, obesity, and clinical evaluation for the treatment of neurodegenerative diseases.

Stress-induced alterations in HPA-axis reactivity and mesolimbic reward activation in individuals with emotional eating

BACKGROUND

Emotional eating has emerged as a contributing factor to overeating, potentially leading to obesity or disordered eating behaviors. However, the underlying biological mechanisms related to emotional eating remain unclear. The present study examined emotional, hormonal, and neural alterations elicited by an acute laboratory stressor in individuals with and without emotional eating.

METHODS

Emotional (n = 13) and non-emotional eaters (n = 15) completed two main study visits, one week apart: one visit included a Stress version and the other a No-stress version of the Maastricht Acute Stress Task (MAST). Immediately pre- and post-MAST, blood was drawn for serum cortisol and participants rated their anxiety level. After the MAST, participants completed a Food Incentive Delay (FID) task during functional magnetic resonance imaging (fMRI), followed by an ad libitum snack period.

RESULTS

Emotional eaters exhibited elevated anxiety (p = 0.037) and cortisol (p = 0.001) in response to the Stress MAST. There were no changes in anxiety or cortisol among non-emotional eaters in response to the Stress MAST or in either group in response to the No-stress MAST. In response to the Stress MAST, emotional eaters exhibited reduced activation during anticipation of food reward in mesolimbic reward regions (caudate: p = 0.014, nucleus accumbens: p = 0.022, putamen: p = 0.013), compared to non-emotional eaters. Groups did not differ in snack consumption.

CONCLUSIONS

These data indicate disrupted neuroendocrine and neural responsivity to psychosocial stress amongst otherwise-healthy emotional eaters, who demonstrated hyperactive HPA-axis response coupled with hypoactivation in reward circuitry. Differential responsivity to stress may represent a risk factor in the development of maladaptive eating behaviors.

The impact of environmental sounds on food reward

Wanting and liking are both components of food reward, but they manifest in fundamentally different neural substrates. While wanting denotes anticipatory and motivational behaviors, liking is associated with consummatory and hedonic experiences. These distinct constructs have also been quantitatively dissociated in behavioral paradigms. Indeed, internal, physiological, and interoceptive states affect the degree to which the food presented is valued. However, how contextual sensory cues might impact these appetitive and rewarding responses to food remains unexplored. In light of the increasing empirical focus on sound in food research, we investigated the influence of environmental soundscapes on explicit liking, explicit wanting, implicit wanting, choice frequency, and reaction time of healthy/unhealthy food using an online version of the Leeds Food Preference Questionnaire (LFPQ). Soft nature sounds and loud restaurant noises were employed to induce emotional relaxation and arousal respectively. One hundred and one healthy university students completed a repeated-measure design of the LFPQ; once with each soundscape playing in the background. Generalized linear mixed model analyses detected a significant interaction effect between soundscape and food type on choice frequency, yet the post hoc analyses did not reach significance. No interaction effects between soundscape and food type on wanting or liking were discovered. However, hypothesis-driven analyses found that nature sounds increased explicit liking of healthy (vs. unhealthy) foods, while no effect of soundscape on any wanting measures (explicit or implicit) were observed. Finally, exploratory analyses indicated that restaurant noise (vs. nature sound) induced faster response times for both healthy and unhealthy foods. The study exemplifies that in an online setting, contextual auditory manipulation of certain food reward measures and decision processes is feasible.

Identification of Novel Neurocircuitry Through Which Leptin Targets Multiple Inputs to the Dopamine System to Reduce Food Reward Seeking

BACKGROUND

Leptin reduces the motivation to obtain food by modulating activity of the mesolimbic dopamine (DA) system upon presentation of cues that predict a food reward. Although leptin directly reduces the activity of ventral tegmental area (VTA) DA neurons, the majority of leptin receptor (LepR)-expressing DA neurons do not project to the nucleus accumbens, the projection implicated in driving food reward seeking. Therefore, the precise locus of leptin action to modulate motivation for a food reward is unresolved.

METHODS

We used transgenic mice expressing Cre recombinase under the control of the LepR promoter, anatomical tracing, optogenetics-assisted patch-clamp electrophysiology, in vivo optogenetics with fiber photometric calcium measurements, and chemogenetics to unravel how leptin-targeted neurocircuitry inhibits food reward seeking.

RESULTS

A large number of DA neurons projecting to the nucleus accumbens are innervated by local VTA LepR-expressing GABA (gamma-aminobutyric acid) neurons. Leptin enhances the activity of these GABA neurons and thereby inhibits nucleus accumbens-projecting DA neurons. In addition, we find that lateral hypothalamic LepR-expressing neurons projecting to the VTA are inhibited by leptin and that these neurons modulate DA neurons indirectly via inhibition of VTA GABA neurons. In accordance with such a disinhibitory function, optogenetically stimulating lateral hypothalamic LepR projections to the VTA potently activates DA neurons in vivo. Moreover, we found that chemogenetic activation of lateral hypothalamic LepR neurons increases the motivation to obtain a food reward only when mice are in a positive energy balance.

CONCLUSIONS

We identify neurocircuitry through which leptin targets multiple inputs to the DA system to reduce food reward seeking.

Key role for hypothalamic interleukin-6 in food-motivated behavior and body weight regulation

The pro-inflammatory role of interleukin-6 (IL-6) is well-characterized. Blockade of IL-6, by Tocilizumab, is used in patients with rheumatoid arthritis and those diagnosed with cytokine storm. However, brain-produced IL-6 has recently emerged as a critical mediator of gut/adipose communication with the brain. Central nervous system (CNS) IL-6 is engaged by peripheral and central signals regulating energy homeostasis. IL-6 is critical for mediating hypophagia and weight loss effects of a GLP-1 analog, exendin-4, a clinically utilized drug. However, neuroanatomical substrates and behavioral mechanisms of brain IL-6 energy balance control remain poorly understood. We propose that the lateral hypothalamus (LH) is an IL-6-harboring brain region, key to food intake and food reward control. Microinjections of IL-6 into the LH reduced chow and palatable food intake in male rats. In contrast, female rats responded with reduced motivated behavior for sucrose, measured by the progressive ratio operant conditioning test, a behavioral mechanism previously not linked to IL-6. To test whether IL-6, produced in the LH, is necessary for ingestive and motivated behaviors, and body weight homeostasis, virogenetic knockdown by infusion of AAV-siRNA-IL6 into the LH was utilized. Attenuation of LH IL-6 resulted in a potent increase in sucrose-motivated behavior, without any effect on ingestive behavior or body weight in female rats. In contrast, the treatment did not affect any parameters measured (chow intake, sucrose-motivated behavior, locomotion, and body weight) in chow-fed males. However, when challenged with a high-fat/high-sugar diet, the male LH IL-6 knockdown rats displayed rapid weight gain and hyperphagia. Together, our data suggest that LH-produced IL-6 is necessary and sufficient for ingestive behavior and weight homeostasis in male rats. In females, IL-6 in the LH plays a critical role in food-motivated, but not ingestive behavior control or weight regulation. Thus, collectively these data support the idea that brain-produced IL-6 engages the hypothalamus to control feeding behavior.

Assessing the role of ghrelin and the enzyme ghrelin O-acyltransferase (GOAT) system in food reward, food motivation, and binge eating behavior

The peripheral peptide hormone ghrelin is a powerful stimulator of food intake, which leads to body weight gain and adiposity in both rodents and humans. The hormone, thus, increases the vulnerability to obesity and binge eating behavior. Several studies have revealed that ghrelin's functions are due to its interaction with the growth hormone secretagogue receptor type 1a (GHSR1a) in the hypothalamic area; besides, ghrelin also promotes the reinforcing properties of hedonic food, acting at extra-hypothalamic sites and interacting with dopaminergic, cannabinoid, opioid, and orexin signaling. The hormone is primarily present in two forms in the plasma and the enzyme ghrelin O-acyltransferase (GOAT) allows the acylation reaction which causes the transformation of des-acyl-ghrelin (DAG) to the active form acyl-ghrelin (AG). DAG has been demonstrated to show antagonist properties; it is metabolically active, and counteracts the effects of AG on glucose metabolism and lipolysis, and reduces food consumption, body weight, and hedonic feeding response. Both peptides seem to influence the hypothalamic-pituitary-adrenal (HPA) axis and the corticosterone/cortisol level that drive the urge to eat under stressful conditions. These findings suggest that DAG and inhibition of GOAT may be targets for obesity and bingeing-related eating disorders and that AG/DAG ratio may be an important potential biomarker to assess the risk of developing maladaptive eating behaviors.

Anxiety-like behavior in female mice is modulated by STAT3 signaling in midbrain dopamine neurons

The central signaling actions of cytokines are mediated by signal transducer and activator of transcription (STAT3). STAT3 activation plays a pivotal role in the behavioral responses to the adiposity hormone leptin, including in midbrain dopamine (DA) neurons where it mediates the influence of leptin to diminish physical activity and running reward in male mice. Leptin also has anxiolytic effects which have been tied to the mesolimbic DA system. To assess the contribution of STAT3 signaling in mesolimbic DA neurons on feeding, mesolimbic DA tone and anxiodepressive behaviors in female mice, we generated DA-specific STAT3 knockout mice by crossing mice expressing Cre under the control of the dopamine transporter with STAT3-LoxP mice. Feeding, locomotion, wheel running, conditioned place preference for palatable food and amphetamine locomotor sensitization were unaffected by DA-specific STAT3 deletion. Conversely, knockout mice exhibited heightened anxiety-like behavior (open field test and elevated plus maze) along with increased basal and stress-induced plasma corticosterone, whereas indices of behavioral despair (forced swim and tail-suspension tasks) were unchanged. In accordance with biochemical evidence of increased D1 receptor signaling (phospho-DARPP32_Thr34) in the central nucleus of the amygdala (CeA) of knockout mice, local microinjections of a D1 receptor antagonist reversed the anxiogenic phenotype of knockout mice. In addition to alluding to sex differences in the signaling mechanisms mediating anxiety-like behavior, our findings suggest that activation of STAT3 in midbrain dopamine neurons projecting to the CeA dampens anxiety in a D1R-dependent manner in female mice.

Food reward depends on TLR4 activation in dopaminergic neurons

The rising prevalence of obesity and being overweight is a worldwide health concern. Food reward dysregulation is the basic factor for the development of obesity. Dopamine (DA) neurons in the ventral tegmental area (VTA) play a vital role in food reward. Toll-like receptor 4 (TLR4) is a transmembrane pattern recognition receptor that can be activated by saturated fatty acids. Here, we show that the deletion of TLR4 specifically in DA neurons increases body weight, increases food intake, and decreases food reward. Conditional deletion of TLR4 also decreased the activity of DA neurons while suppressing the expression of tyrosine hydroxylase (TH) in the VTA, which regulates the concentration of DA in the nucleus accumbens (NAc) to affect food reward. Meanwhile, AAV-Cre-GFP mediated VTA-specific TLR4-deficient mice recapitulates food reward of DAT-TLR4-KO mice. Food reward could be rescued by re-expressing TLR4 in VTA DA neurons. Moreover, effects of intra-VTA infusion of lauric acid (a saturated fatty acid with 12 carbon) on food reward were abolished in mice lacking TLR4 in DA neurons. Our study demonstrates the critical role of TLR4 signaling in regulating the activity of VTA DA neurons and the normal function of the mesolimbic DA system that may contribute to food reward.

The effect of alcohol on food-related attentional bias, food reward and intake: Two experimental studies

Acute alcohol consumption has been shown to increase food intake, and long-term alcohol consumption may be a risk for weight gain. A potential, but under-studied, mechanism for this effect is alcohol's ability to enhance food reward. In two studies, participants consumed an alcoholic drink (Study 1: 0.3 grams of alcohol per kilogram of bodyweight (g/kg); Study 2: 0.6 g/kg) and a placebo-alcohol drink in a within-subjects design. In both studies, food-related appetitive and motivational states, and attentional bias (AB) towards food-related cues were measured. In Study 1 (N = 44), participants completed a visual probe task with concurrent recording of eye-movements which measured AB towards images of palatable foods, unpalatable foods, and non-food control items. Participants also completed measures of appetite and snack urge ratings, salivary response towards palatable foods and an ad libitum food taste test. In Study 2 (N = 84), participants completed a similar procedure, but completed a modified Stroop task which measured differences in food-related and alcohol-related AB across the two drink conditions. In Study 1, there was no difference in food-related AB between drink conditions, and no differences in snack urge, appetite ratings, salivary response, or food intake. In contrast, Study 2 showed an alcohol-induced increase in AB towards food, but not alcohol. Snack urge, alcohol urge ratings and ad libitum food intake were also higher after alcohol consumption, relative to the placebo. Collectively, these findings suggest that alcohol can increase food reward and food intake, but these effects may only occur at a higher dose.

Selective serotonin receptor stimulation of the ventral tegmentum differentially affects appetitive motivation for sugar on a progressive ratio schedule of reinforcement

Serotonin signaling influences satiety and motivation through known actions in the hindbrain and hypothalamus. Recently, we reported that some classes of serotonin receptors also modulate food intake through actions in the ventral tegmentum and the nucleus accumbens. In the current experiments, we examined whether activation or blockade of individual serotonin receptor subtypes in the ventral tegmentum might also affect appetitive motivation for sugar pellets as assessed in a progressive ratio (PR) task. Separate groups of rats were tested following stimulation or blockade of ventral tegmental serotonin 1A, 1B, 2A, 2B, 2C, or 3 receptors. Rats within each group received multiple doses of a single drug across days; each test was separated by 72 h. Progressive ratio break point was significantly affected by stimulation of ventral tegmental serotonin 1A receptors with 8-OH-DPAT (0, 2, 4, 8 μg/side) or stimulation of serotonin 3 receptors with mCPBG (0, 10, & 20 μg/side). High doses of both agents tended to decrease break point. Additionally, stimulation of serotonin 2C receptors with RO60-0175 (at 0, 2, and 5 μg/side) reduced total lever presses and demonstrated a trend towards reducing break point. There were no effects of stimulating ventral tegmental serotonin 1B, 2A, or 2B receptors on break point; neither did antagonism of any of the serotonin receptor subtypes significantly affect performance. These data provide additional evidence that serotonergic signaling in the mesolimbic pathway affects motivated behavior, and demonstrate that a subset of serotonin receptors impact not only food consumption, but appetitive food-seeking as well.

Nucleus accumbens melanin-concentrating hormone signaling promotes feeding in a sex-specific manner

Melanin-concentrating hormone (MCH) is an orexigenic neuropeptide produced in the lateral hypothalamus and zona incerta that increases food intake. The neuronal pathways and behavioral mechanisms mediating the orexigenic effects of MCH are poorly understood, as is the extent to which MCH-mediated feeding outcomes are sex-dependent. Here we investigate the hypothesis that MCH-producing neurons act in the nucleus accumbens shell (ACBsh) to promote feeding behavior and motivation for palatable food in a sex-dependent manner. We utilized ACBsh MCH receptor (MCH1R)-directed pharmacology as well as a dual virus chemogenetic approach to selectively activate MCH neurons that project to the ACBsh. Results reveal that both ACBsh MCH1R activation and activating ACBsh-projecting MCH neurons increase consumption of standard chow and palatable sucrose in male rats without affecting motivated operant responding for sucrose, general activity levels, or anxiety-like behavior. In contrast, food intake was not affected in female rats by either ACBsh MCH1R activation or ACBsh-projecting MCH neuron activation. To determine a mechanism for this sexual dimorphism, we investigated whether the orexigenic effect of ACBsh MCH1R activation is reduced by endogenous estradiol signaling. In ovariectomized female rats on a cyclic regimen of either estradiol (EB) or oil vehicle, ACBsh MCH1R activation increased feeding only in oil-treated rats, suggesting that EB attenuates the ability of ACBsh MCH signaling to promote food intake. Collective results show that MCH ACBsh signaling promotes feeding in an estrogen- and sex-dependent manner, thus identifying novel neurobiological mechanisms through which MCH and female sex hormones interact to influence food intake.

Diet containing stearic acid increases food reward-related behaviors in mice compared with oleic acid

Obesity is currently a worldwide phenomenon. The consumption of calorie-rich foods is responsible for most obesity cases, but not all humans exposed to high-calorie diets develop obesity. According to recent studies, exposure to fat-rich diets may be the actual cause of obesity. Dietary long-chain fatty acids affect brain function and are linked to food intake and motivation-related behaviors. Recently, many studies have shown that different types of fatty acids play different roles in animals. In our study, the effects of stearic acid (a saturated fatty acid) and oleic acid (a monounsaturated fatty acid) in diets on hedonic feeding behaviors were investigated, and changes of feeding-related protein levels in the brain were detected to explore the possible mechanism underlying the effects of these fatty acids. As a result, mice fed a diet containing stearic acid, compared to a diet containing oleic acid, exhibited increased food intake, hedonic eating, and an operant response to sucrose and locomotor activity. Furthermore, stearic acid corresponded to a higher level of leptin in serum than oleic acid. In addition, the stearic acid treated group had lower protein levels of p-JAK2 and p-STAT3 in the VTA and a higher dopamine concentration in the NAc than the oleic acid-treated group. Meanwhile, the protein level of TH in the NAc was higher and the protein level of the DA transporter in the VTA was lower in the stearic acid-fed group than in the oleic acid-fed group. In conclusion, these findings indicated that a diet containing stearic acid can increase hedonic feeding behavior and affect mesolimbic dopamine system signals in mice. Moreover, the lowering of serum leptin and leptin signaling in the VTA may contribute to this effect.

The effect of transcranial direct current stimulation (tDCS) on food craving, reward and appetite in a healthy population

The ability to control hedonic appetite is associated with executive functioning, originating in the prefrontal cortex (PFC). These rewarding components of food can override homeostatic mechanisms, potentiating obesogenic behaviours. Indeed, those susceptible to overconsumption appear to have PFC hypo-activation. Transcranial direct current stimulation (tDCS) over the dorsolateral PFC (DLPFC) has been shown to reduce food craving and consumption, potentially via attenuating this reward response. We examined the effects of stimulation on food reward and craving using a healthy-weight cohort. This study is amongst the first to explore the effects of tDCS on explicit and implicit components of reward for different food categories. Twenty-one healthy-weight participants (24 ± 7 years, 22.8 ± 2.3 kg m^-2) completed two sessions involving double-blind, randomised and counterbalanced anodal or sham tDCS over the right DLPFC, at 2 mA for 20 min. Food craving (Food Craving Questionnaire-State), reward (Leeds Food Preference Questionnaire), and subjective appetite (100 mm visual analogue scales) were measured pre- and post-tDCS. Eating behaviour trait susceptibility was assessed using the Three Factor Eating Questionnaire-Short Form, Control of Eating Questionnaire, and Food Craving Questionnaire-Trait-reduced. Stimulation did not alter food craving, reward or appetite in healthy-weight participants who displayed low susceptibility to overconsumption, with low trait craving, good craving control, and low uncontrolled eating and emotional eating behaviour. Implicit and explicit reward were reliable measures of hedonic appetite, suggesting these are robust targets for future tDCS research. These findings suggest that applying tDCS over the DLPFC does not change food reward response in individuals not at risk for overconsumption, and future work should focus on those at risk of overconsumption who may be more responsive to the effects of tDCS on hedonic appetite.

Effect of a 10-month residential multidisciplinary weight loss intervention on food reward in adolescents with obesity

BACKGROUND

While multidisciplinary weight loss (WL) programs have been suggested to improve the sensitivity of appetite control system, this study examined for the first time the effect of a specific multidisciplinary intervention on the hedonic aspects of food intake in adolescents with obesity.

STUDY DESIGN

Twenty-four adolescents (11-15 years) with obesity (mean BMI: 35.7 ± 4.5 kg/m²; BMI percentile: 98.7 ± 0.5) took part in a 10-month inpatient WL program, which included physical activity, nutritional education and psychological support. Height, weight, body composition, food reward (pre- and post-meal), ad libitum energy intake, appetite sensations and eating behavior traits were assessed at baseline, 5 months and at the end of the 10-month intervention. Analyses were conducted with linear mixed models and paired t-tests.

RESULTS

The mean WL was 8.9 ± 6.9 kg. Appetite sensations and pre-meal hedonic ratings of liking for all food categories (HF: high-fat; LF: low-fat; SA: savory; SW: sweet) increased after 5 months (fasting hunger, p = 0.02; fasting desire to eat, p = 0.01; daily hunger, p = 0.001; pre-meal liking for HFSA, p = 0.03; LFSA, p = 0.04; HFSW, p = 0.009; LFSW, p = 0.005). In contrast, appetite sensations (fasting and daily), emotional eating (p < 0.001), uncontrolled eating (p = 0.009), and pre-meal explicit liking (for all food categories) decreased between months 5 and 10. Post-meal liking for HFSA (p < 0.001), LFSA (p = 0.002), HFSW (p = 0.02) and LFSW (p < 0.001) decreased between baseline and month 5 and remained unchanged between months 5 and 10.

CONCLUSION

These findings suggest that adaptive mechanisms to WL occurring in the short-to-medium term are attenuated in the longer term with the persistence of WL. These results indicate improvements in the reward response to food in adolescents with obesity and may contribute to the beneficial effect of multicomponent WL interventions in this population. Future studies are required to confirm these findings and elucidate underlying mechanisms.

Pro-social preference in an automated operant two-choice reward task under different housing conditions: Exploratory studies on pro-social decision making

In this study, we aimed to develop a behavioral task that measures pro-social decision making in rats. A fully automated, operant pro-social two-choice task is introduced that quantifies pro-social preferences for a mutual food reward in a set-up with tightly controlled task contingencies. Pairs of same-sex adult Wistar rats were placed in an operant chamber divided into two compartments (one rat per compartment), separated by a transparent barrier with holes that allowed the rats to see, hear, smell, but not touch each other. Test rats could earn a sucrose pellet either for themselves (own reward) or for themselves and the partner (both reward) by means of lever pressing. On average, male rats showed a 60 % preference for the lever that yielded a food reward for both themselves and their partner. In contrast, females did not show lever preference, regardless of the estrous cycle phase. Next, the impact of juvenile environmental factors on male rat social decision making was studied. Males were group-housed from postnatal day 26 onwards in complex housing Marlau™ cages that provided social and physical enrichment and stimulation in the form of novelty. Complex housed males did not show a preference for the pro-social lever.

Does exercising before or after a meal affect energy balance in adolescents with obesity?

BACKGROUND AND AIM

Exercise timing has been suggested to affect appetite and energy intake (EI). The aim of this study was to examine the impact of exercising immediately before or after a meal on EI, appetite sensations and food reward (FR) in adolescents with obesity.

METHODS AND RESULTS

Seventeen adolescents with obesity completed 3 experimental sessions (randomized controlled trial): rest + lunch (CON); exercise + lunch (EX-MEAL); lunch + exercise (MEAL-EX). The exercise consisted of cycling 30 min at 65%V̇O_2peak. Outcomes included ad libitum EI (weighed lunch and dinner), FR (Leeds Food Preference Questionnaire at pre- and post-combination of exercise/rest and lunch, and pre-dinner) and appetite sensations (visual analogue scales). EI was not different between conditions. Compared with CON, relative EI at lunch was lower in EX-MEAL and MEAL-EX (p ≤ 0.05) and daily only in MEAL-EX (p < 0.01). Postprandial fullness was higher in EX-MEAL compared to CON. Compared with CON, both EX-MEAL and MEAL-EX attenuated the increase in wanting for sweet food and reduced explicit liking for fat.

CONCLUSIONS

These preliminary results suggest that exercising immediately before or after a meal produce few differences in appetite and have small beneficial effects on overall energy balance in adolescents with obesity, as well as on FR.

CLINICAL TRIALS

NCT03967782.

The Impact of Physical Activity on Food Reward: Review and Conceptual Synthesis of Evidence from Observational, Acute, and Chronic Exercise Training Studies

PURPOSE OF REVIEW

This review brings together current evidence from observational, acute, and chronic exercise training studies to inform public debate on the impact of physical activity and exercise on food reward.

RECENT FINDINGS

Low levels of physical activity are associated with higher liking and wanting for high-energy food. Acute bouts of exercise tend to reduce behavioral indices of reward for high-energy food in inactive individuals. A dissociation in liking (increase) and wanting (decrease) may occur during chronic exercise training associated with loss of body fat. Habitual moderate-to-vigorous physical activity is associated with lower liking and wanting for high-fat food, and higher liking for low-fat food. Food reward does not counteract the benefit of increasing physical activity levels for obesity management. Exercise training appears to be accompanied by positive changes in food preferences in line with an overall improvement in appetite control.

Food is discounted more steeply than money: Evidence from N2 and P3 responses in delay discounting tasks

In decision making, different rewards such as money and food may lead to different behavioral outcomes and neural dynamics. In this study, we used event-related potential (ERP) techniques and delay discounting tasks with money and snacks as rewards to determine whether there are differences in behavior and neurophysiology across the two tasks. The results showed that participants not only behaved differently but also showed different neural patterns in the money and snack tasks. In particular, at the behavioral level, participants discounted snacks more than money. At the neural level, the N2 amplitudes in the snack task were more negative than those in the money task. It was also discovered that for females, the amplitudes of P3 in the snack task were larger than those in money, while there was no difference for males. The current study showed the essential roles of frontal cognitive control function during varied delay discounting processes on money and food rewards.

Circadian modulation of motivation in mice

Most living organisms have a circadian timing system adapted to optimize the daily rhythm of exposure to the environment. This circadian system modulates several behavioral and physiological processes, including the response to natural and drug rewards. Food is the most potent natural reward across species. Food-seeking is known to be mediated by dopaminergic and serotonergic transmission in cortico-limbic pathways. In the present work, we show evidence of a circadian modulation of motivation for food reward in young (4-months old) and aged (over 1.5 years old) C57BL/6 mice. Motivation was assayed through the progressive ratio (PR) schedule. Mice under a 12:12 light/dark (LD) cycle exhibited a diurnal rhythm in motivation, becoming more motivated during the night, coincident with their active phase. This rhythm was also evident under constant dark conditions, indicating the endogenous nature of this modulation. However, circadian arrhythmicity induced by chronic exposure to constant light conditions impaired the performance in the task causing low motivation levels. Furthermore, the day/night difference in motivation was also evident even without caloric restriction when using a palatable reward. All these results were found to be unaffected by aging. Taken together, our results indicate that motivation for food reward is regulated in a circadian manner, independent of the nutritional status and the nature of the reward, and that this rhythmic modulation is not affected by aging. These results may contribute to improve treatment related to psychiatric disorders or drugs of abuse, taking into account potential mechanisms of circadian modulation of motivational states.

Different periods of forced abstinence after instrumental learning for food reward of different macronutrient value on responding for conditioned cues and AMPAr subunit levels

Food craving can be viewed as an intense desire for a specific food that propagates seeking and consuming behavior. Prolonged forced abstinence from rewarding foods can result in escalated food-seeking behavior as measured via elevated responding for food-paired cues in the absence of the primary reward. Palatable food consumption and food-seeking is associated with changes in the abundance and composition of AMPA receptors in the nucleus accumbens (NAc) but differing results have been reported. The present study examined whether different food types could produce escalated food-seeking behavior after various abstinence periods and whether this was associated with changes in AMPA receptor protein levels. Rats were trained for 10 days to bar press for purified, sucrose, or chocolate-flavored sucrose pellets. Rats were tested at 24 hrs, 7 d or 14 d whereby bar pressing resulted in presentation of cues paired with food but no food reward was delivered. Western blotting was used to determine protein levels of GluR1, GluR1pSer845, and GluR2 in the NAc. Three separate groups were assessed: 1) a group that was trained on the operant task and tested for conditioned responding (tested group); 2) a group that was trained on the operant task but not tested (non-tested group); 3) a group that was neither trained nor tested (control). The purified food group showed a time-dependent elevation in conditioned bar pressing over the 3 abstinence periods. GluR1 AMPAr subunit levels were higher in the purified and sucrose groups tested at 24 hours compared to the non-tested and control values. GluR1 levels subsequently declined at the 7- and 14-day abstinence periods in the purified and sucrose tested and non-tested groups compared to control values. GluR2 and pSer845 Glur1 levels were similar across all groups and abstinence periods. These results show that food-seeking behavior associated with forced abstinence from different food rewards may depend on the macronutrient composition of the food reward or the food type given during the abstinence period. A clear link with AMPAr subunit levels in this model was not established.

Attentional bias to food varies as a function of metabolic state independent of weight status

Eating behaviour requires that internal metabolic changes are recognized by the central nervous system which regulates brain responses to food cues. This function may be altered in obesity. The aim of this study was to examine potential differences in neurocognitive responses to visual food cues as a function of metabolic state and weight status. A crossover study with two participant groups was conducted, one group with normal-weight (n = 20) and one group with overweight/obesity (n = 22), who completed a novel battery of neurocognitive tests assessing food-cue elicited behavior in both fasted and fed states. The test battery included a visual-dot probe task (VPT), a stimulus-response compatibility task (SRCT) and an implicit association task (IAT). Results from the VPT showed a significant main effect of metabolic state on attentional bias (F(1,40) = 9.90, p = .003, η²_p = .198), with participants in the fasted state showing a significantly greater attentional bias for food stimuli than in the fed state. No significant main effect of metabolic state on approach food bias, assessed via the SRCT, or implicit attitudes to food cues, assessed via the IAT, was found and overall, no difference in neurocognitive processing of food cues was demonstrated between participant groups. In the fed state, attentional bias to food cues decreases in both normal-weight controls and participants with overweight/obesity, indicating that changes in current metabolic state can be reflected in attentional processing of visual food cues independently of weight status. Neurocognitive tasks which can effectively and sensitively identify differences in food cue perception according to changes in metabolic status will be useful tools in exploring more complicated interactions between homeostatic and hedonic drives of food intake.

Introducing eccentric cycling during a multidisciplinary weight loss intervention might prevent adolescents with obesity from increasing their food intake: The TEXTOO study

PURPOSE

The present study compared the appetite responses to an inpatient eccentric vs. concentric cycling training programs in adolescents with obesity.

METHODS

24 adolescents with obesity (12-16yrs; Tanner 3-4) followed a 12-week multidisciplinary intervention (Phase1), after which they were randomized to concentric (CON) or eccentric (ECC) training for 12 weeks (Phase2). Assessment of anthropometrics, body composition (DXA), aerobic power (VO_2max), energy (EI) and macronutrient intake, food reward, and subjective appetite were performed at baseline, and after Phase1 (T1) and Phase2 (T2).

RESULTS

Body mass, BMI, and fat mass (FM%) decreased in both groups (p < 0.001). FM% reduction was greater in ECC at T2 (-9.9%). EI did not change in either group at T1, but was greater at T2 relative to T1 in CON only (p < 0.001,+22%). There was no correlation between the change in body mass, FM%, fat-free mass and EI. Hunger (p = 0.002) and desire to eat (p = 0.001) were higher in CON vs. ECC with no time effects nor interactions. Prospective food consumption increased in both groups with no group effect nor interaction. Satiety was not different between groups or over time. In ECC, preference for high-fat foods increased (p = 0.03), and preference (p = 0.004) and implicit wanting (p = 0.016) for sweet foods decreased.

CONCLUSION

Eccentric cycling as part of an inpatient multidisciplinary weight-loss intervention might help prevent increased ad libitum energy intake compared to concentric exercise training in adolescents with obesity, potentially through distinct effects of the food reward system.

Neuropsychiatric implications of transient receptor potential vanilloid (TRPV) channels in the reward system

Neuropsychiatric disorders (NPDs) exert a devastating impact on an individual's personal and social well-being, encompassing various conditions and brain anomalies that influence affect, cognition, and behavior. Because the pathophysiology of NPDs is multifactorial, the precise mechanisms underlying the development of such disorders remain unclear, representing a unique challenge in current neuropsychopharmacotherapy. Transient receptor potential vanilloid (TRPV) type channels are a family of ligand-gated ion channels that mainly include sensory receptors that respond to thermal, mechanical and chemical stimuli. TRPV channels are abundantly present in dopaminergic neurons, thus playing a pivotal role in the modulation of the reward system and in pathophysiology of diseases such as stress, anxiety, depression, schizophrenia, neurodegenerative disorders and substance abuse/addiction. Recent evidence has highlighted TRPV channels as potential targets for understanding modulation of the reward system and various forms of addiction (opioids, cocaine, amphetamines, alcohol, nicotine, cannabis). In this review, we discuss the distribution, physiological roles, ligands and therapeutic importance of TRPV channels with regard to NPDs and addiction biology.

Effects of Roux-en-Y Gastric Bypass and Sleeve Gastrectomy on Food Preferences and Potential Mechanisms Involved

PURPOSE OF REVIEW

Bariatric surgery leads to a substantial decrease in energy intake. It is unclear whether this decrease in energy intake is simply due to eating smaller portions of the same food items or a shift in food preference towards less energy-dense foods. This review evaluates the existing literature on changes in food preferences after bariatric surgery and the potential mechanisms involved.

RECENT FINDINGS

Changes in food preferences have been reported; however, the evidence is mainly based on indirect measurements, such as self-reporting. When changes in food preferences are directly assessed, results contradict previous findings, indicating that results based on self-reporting must be interpreted with caution as they do not necessarily reflect actual behaviour. However, it seems that there could be inter-individual differences in the response to surgery. Future studies investigating changes in food preferences should not only focus on direct measured of behaviour but should also consider the heterogeneity of the response after bariatric surgery.

Peripheral nerve injury in rats induces alternations in choice behavior associated with food reinforcement

Operant methods that allow animals to avoid painful stimuli are interpreted to assess the aversive quality of pain; however, such measurements require investigator-initiated stimuli to animals. Here we developed a shuttle maze test to repeatedly assess activity associated nociception without forced stimulation. Rats ambulate back and forth between two treat feeders by taking either a short route with a prickly surfaced arch or a longer route with a smooth floor. L5-L6 spinal nerve ligation (SNL) reduced the preference for the short route with the arch, correlated with hypersensitivity in the hind paw. Oral gabapentin restored the short route preference and reduced hypersensitivity in SNL rats, and blockade of spinal α2-adrenoceptors reduced gabapentin's effects on hypersensitivity but not on preference index. These results suggest that SNL injury alters behavior in the shuttle maze test and that the shuttle maze test shows comparable results to reflexive hypersensitivity after SNL in magnitude and response to gabapentin.

Appetitive characteristics in children with cystic fibrosis: Questionnaire validation and associations with nutritional status

BACKGROUND

Appetitive characteristics are an important factor in the nutritional status of children with cystic fibrosis (CF). We administered a brief parent-report eating behavior questionnaire, validated in healthy children, to determine the relationship between appetitive characteristics and body weight in children with CF.

METHODS

Parents of children attending the Johns Hopkins Pediatric CF Clinic completed the Child Eating Behavior Questionnaire (CEBQ) at a routine clinic visit. Responses were correlated with anthropometric and other clinical data.

RESULTS

Parents of 64 children with CF aged 7.74 ± 3.17 years (mean ± SD) completed the CEBQ. The CEBQ subscales demonstrated good internal consistency (Cronbach's α = 0.76-0.94). Higher scores on food avoidance subscales (Slowness in Eating) were associated with lower body mass index (BMI) z-scores, and higher scores on food approach subscales (Food Responsiveness, Enjoyment of Food, Emotional Overeating) with higher BMI z-scores. Children with feeding aids (i.e. gastric tube or appetite-stimulating medications) demonstrated greater food avoidance (Slowness in Eating) and lesser food approach (Enjoyment of Food) when compared to those without feeding aids. Children with pancreatic insufficiency also demonstrated greater food avoidance (Slowness in Eating).

CONCLUSIONS

The CEBQ can be used in a clinical setting to identify children with CF with appetitive characteristics associated with difficulty gaining weight. These children could potentially benefit from earlier interventions to aid in weight gain. Characterization of appetite using the CEBQ could aid investigation of the biological etiology of low appetite, and optimization of clinical and parental approaches to achieving a healthy nutritional status.

Food portion size influences accompanying beverage selection in adults

When trying to reduce food portion size, it is important that meal satisfaction is, as far as possible, preserved. Otherwise, individuals may select accompaniments to the meal (e.g., snacks, beverages) to achieve satisfaction and, in doing so, negate any benefit of the original portion size reduction. This study investigated whether varying portion sizes of food would influence choice of accompanying beverages. That is, when presented with a food portion size that is smaller or larger than their ideal, an individual may compensate by choosing a beverage based on its satiating and/or orosensory properties to balance the expected satiation and satisfaction of a meal. Data from an online interactive study (n = 93) was analysed using multilevel ordinal logistic regression models. Food portion size (100, 300, 500, 700, or 900 kcal) predicted beverage choice (water, low-energy sweetened beverage, high-energy sweetened beverage). For example, the sweetened beverages were more likely to be selected with small food portion sizes (p < .001). Participant ideal food portion size did not interact with this relationship. Participants appear to have recognised that sweetened beverages provide flavour and/or energy, and used them to compensate for a smaller meal. While switching to a low-energy beverage with an increased food portion size is advantageous for energy balance, choosing a high-energy beverage with a decreased food portion size is likely to be detrimental for those attempting to reduce energy intake and body weight.

GLP-1/dexamethasone inhibits food reward without inducing mood and memory deficits in mice

BACKGROUND

Pharmacotherapies targeting motivational aspects of feeding and palatable food reward, while sparing mood and cognitive function, represent an alluring approach to reverse obesity and maintain weight loss in an obesogenic environment. A novel glucagon-like peptide-1/dexamethasone (GLP-1/Dexa) conjugate, developed to selectively activate glucocorticoid receptors in GLP-1 receptor-expressing cells was shown to decrease food intake and lower body weight in obese mice. Here, we investigate if this novel drug candidate modulates the rewarding properties of food and if it affects behavioral indices of mood and memory.

METHODS

C57Bl6 mice treated with the GLP-1/Dexa conjugate, GLP-1 or vehicle lever-pressed for high-fat, high sugar (HFHS) food rewards in an operant task. Alterations in food-motivated behavior were also assessed following a HFHS diet withdrawal manipulation (switch to chow). The effects of repeated GLP-1/Dexa conjugate, GLP-1 or vehicle on free-feeding intake, body weight, anxiodepressive behaviors (elevated-plus maze, open field test & forced swim test), memory (novel object recognition) and mRNA expression of reward-relevant markers in the nucleus accumbens were also evaluated in mice fed a HFHS diet for 12 weeks.

RESULTS

Mice treated with a GLP-1 analogue displayed a transient (4 h) reduction in their motivation to lever press for HFHS reward, whereas treatment with equimolar doses of GLP-1/Dexa delivered a superior and sustained (20 h) suppression of food-motivated behavior. GLP-1/Dexa also inhibited food reward following withdrawal from the HFHS diet. These benefits coincided with related transcriptional changes of dopaminergic markers in the nucleus accumbens. Importantly, repeated GLP-1/Dexa treatment during a HFHS diet caused weight loss without affecting anxiodepressive behavior and memory.

CONCLUSION

Via its actions to blunt the rewarding effects of palatable food without affecting mood and recognition memory, GLP-1-directed targeting of dexamethasone may serve as a promising and safe anti-obesity strategy.

Ghrelin and food reward

Food intake is tightly regulated by homeostatic and reward mechanisms and the adequate function of both is necessary for the proper maintenance of energy balance. Ghrelin impacts on these two levels to induce feeding. In this review, we present the actions of ghrelin in food reward, including their dependence on other relevant modulators implicated in the motivational aspects of feeding, including dopamine, opioid peptides, and endocannabinoids. We also describe the interaction between brain areas involved in homeostatic regulation of feeding and the reward system, with a special emphasis on the role of arcuate nucleus melanocortins and lateral hypothalamus orexins in ghrelin function. Finally, we briefly discuss the actions of ghrelin in food reward in obesity. We propose that new insights into the mechanism of action of ghrelin in the rewarding and motivational control of food intake will help to understand food-related disorders including obesity and anorexia.

Adiposity and binge eating are related to liking and wanting for food in Brazil: A cultural adaptation of the Leeds food preference questionnaire

The Leeds Food Preference Questionnaire (LFPQ) measures separable psychological components of food reward (Liking and Wanting). In this study a cultural adaptation of the LFPQ for a Brazilian population (LFPQ-BR) was examined by comparing liking and wanting scores in fasted and fed states and their association with adiposity and disturbed eating. A culturally adapted food picture database was validated by an online questionnaire completed by 162 individuals. Cluster analysis verified if the foods were accurately perceived in terms of sweetness, fat and calorie content. Subsequently, 48 male (N = 21) and female (N = 27) adults with mean Body Mass Index 26.6 (0.9) kg/m², and mean age 32.8 (1.4) years, were evaluated by the LFPQ-BR before and after a fixed test meal. The Binge Eating Scale was used to measure binge eating symptoms. There was a decrease in explicit liking, implicit wanting, and explicit wanting scores for food in general in the fed condition. The implicit and explicit wanting and explicit liking scores for high-and-low fat savoury food decreased and for high-and-low fat sweet foods increased to a greater extent after the savoury test meal. Body Mass Index was found to predict implicit wanting for high fat relative to low fat foods. Binge eating symptoms predicted high fat sweet explicit liking and explicit wanting in the fed condition. Finally, high fat sweet preference was found to be sex-related as females had greater implicit wanting for high fat sweet foods in fasted and fed states. The results presented here indicate that the LFPQ-BR is a useful instrument for the evaluation of liking and wanting for food in Brazil.