Effects of fructose vs glucose on regional cerebral blood flow in brain regions involved with appetite and reward pathways

Mechanisms Underlying Memory Impairment Induced by Fructose

Fructose consumption has increased over the years, especially in adolescents living in urban areas. Growing evidence indicates that daily fructose consumption leads to some pathological conditions, including memory impairment. This review summarizes relevant data describing cognitive deficits after fructose intake and analyzes the underlying neurobiological mechanisms. Preclinical experiments show sex-related deficits in spatial memory; that is, while males exhibit significant imbalances in spatial processing, females seem unaffected by dietary supplementation with fructose. Recognition memory has also been evaluated; however, only female rodents show a significant decline in the novel object recognition test performance. According to mechanistic evidence, fructose intake induces neuroinflammation, mitochondrial dysfunction, and oxidative stress in the short term. Subsequently, these mechanisms can trigger other long-term effects, such as inhibition of neurogenesis, downregulation of trophic factors and receptors, weakening of synaptic plasticity, and long-term potentiation decay. Integrating all these neurobiological mechanisms will help us understand the cellular and molecular processes that trigger the memory impairment induced by fructose.

Differential responses of primary neuron-secreted MCP-1 and IL-9 to type 2 diabetes and Alzheimer's disease-associated metabolites

Type 2 diabetes (T2D) is implicated as a risk factor for Alzheimer's disease (AD), the most common form of dementia. In this work, we investigated neuroinflammatory responses of primary neurons to potentially circulating, blood-brain barrier (BBB) permeable metabolites associated with AD, T2D, or both. We identified nine metabolites associated with protective or detrimental properties of AD and T2D in literature (lauric acid, asparagine, fructose, arachidonic acid, aminoadipic acid, sorbitol, retinol, tryptophan, niacinamide) and stimulated primary mouse neuron cultures with each metabolite before quantifying cytokine secretion via Luminex. We employed unsupervised clustering, inferential statistics, and partial least squares discriminant analysis to identify relationships between cytokine concentration and disease-associations of metabolites. We identified MCP-1, a cytokine associated with monocyte recruitment, as differentially abundant between neurons stimulated by metabolites associated with protective and detrimental properties of AD and T2D. We also identified IL-9, a cytokine that promotes mast cell growth, to be differentially associated with T2D. Indeed, cytokines, such as MCP-1 and IL-9, released from neurons in response to BBB-permeable metabolites associated with T2D may contribute to AD development by downstream effects of neuroinflammation.

Neurohormonal response patterns to hunger, satiation, and postprandial fullness in normal weight, anorexia nervosa, and obesity

BACKGROUND

Food intake is regulated by homeostatic and hedonic systems that interact in a complex neuro-hormonal network. Dysregulation in energy intake can lead to obesity (OB) or anorexia nervosa (AN). However, little is known about the neurohormonal response patterns to food intake in normal weight (NW), OB, and AN.

MATERIAL & METHODS

During an ad libitum nutrient drink (Ensure®) test (NDT), participants underwent three pseudo-continuous arterial spin labeling (pCASL) MRI scans. The first scan was performed before starting the NDT after a > 12 h overnight fast (Hunger), the second after reaching maximal fullness (Satiation), and the third 30-min after satiation (postprandial fullness). We measured blood levels of ghrelin, cholecystokinin (CCK), glucagon-like peptide (GLP-1), and peptide YY (PYY) with every pCASL-MRI scan. Semiquantitative cerebral blood flow (CBF) maps in mL/100 gr brain/min were calculated and normalized (nCBF) with the CBF in the frontoparietal white matter. The hypothalamus (HT), nucleus accumbens [NAc] and dorsal striatum [DS] were selected as regions of interest (ROIs).

RESULTS

A total of 53 participants, 7 with AN, 17 with NW (body-mass index [BMI] 18.5-24.9 kg/m2 ), and 29 with OB (BMI ≥30 kg/m2 ) completed the study. The NW group had a progressive decrease in all five ROIs during the three stages of food intake (hunger, satiation, and post-prandial fullness). In contrast, participants with OB showed a minimal change from hunger to postprandial fullness in all five ROIs. The AN group had a sustained nCBF in the HT and DS, from hunger to satiation, with a subsequent decrease in nCBF from satiation to postprandial fullness. All three groups had similar hormonal response patterns with a decrease in ghrelin, an increase in GLP-1 and PYY, and no change in CCK.

CONCLUSION

Conditions of regulated (NW) and dysregulated (OB and AN) energy intake are associated with distinctive neurohormonal activity patterns in response to hunger, satiation, and postprandial fullness.

Fructose: a modulator of intestinal barrier function and hepatic health?

PURPOSE

Consumption of fructose has repeatedly been discussed to be a key factor in the development of health disturbances such as hypertension, diabetes type 2, and non-alcoholic fatty liver disease. Despite intense research efforts, the question if and how high dietary fructose intake interferes with human health has not yet been fully answered.

RESULTS

Studies suggest that besides its insulin-independent metabolism dietary fructose may also impact intestinal homeostasis and barrier function. Indeed, it has been suggested by the results of human and animal as well as in vitro studies that fructose enriched diets may alter intestinal microbiota composition. Furthermore, studies have also shown that both acute and chronic intake of fructose may lead to an increased formation of nitric oxide and a loss of tight junction proteins in small intestinal tissue. These alterations have been related to an increased translocation of pathogen-associated molecular patterns (PAMPs) like bacterial endotoxin and an induction of dependent signaling cascades in the liver but also other tissues.

CONCLUSION

In the present narrative review, results of studies assessing the effects of fructose on intestinal barrier function and their impact on the development of health disturbances with a particular focus on the liver are summarized and discussed.

An oral glucose tolerance test does not affect cerebral blood flow: role of NOS

Animal data indicate that insulin triggers a robust nitric oxide synthase (NOS)-mediated dilation in cerebral arteries similar to the peripheral tissue vasodilation observed in healthy adults. Insulin's role in regulating cerebral blood flow (CBF) in humans remains unclear but may be important for understanding the links between insulin resistance, diminished CBF, and poor brain health outcomes. We tested the hypothesis that an oral glucose challenge (oral glucose tolerance test, OGTT), which increases systemic insulin and glucose, would acutely increase CBF in healthy adults due to NOS-mediated vasodilation, and that changes in CBF would be greater in anterior regions where NOS expression or activity may be greater. In a randomized, single-blind approach, 18 young healthy adults (24 ± 5 yr) underwent magnetic resonance imaging (MRI) with a placebo before and after an OGTT (75 g glucose), and 11 of these adults also completed an NG-monomethyl-l-arginine (l-NMMA) visit. Four-dimensional (4-D) flow MRI quantified macrovascular CBF and arterial spin labeling (ASL) quantified microvascular perfusion. Subjects completed baseline imaging with a placebo (or l-NMMA), then consumed an OGTT followed by MRI scans and blood sampling every 10-15 min for 90 min. Contrary to our hypothesis, total CBF (P = 0.17) and global perfusion (P > 0.05) did not change at any time point up to 60 min after the OGTT, and no regional changes were detected. l-NMMA did not mediate any effect of OGTT on CBF. These data suggest that insulin-glucose challenge does not acutely alter CBF in healthy adults.

Differential responses of primary neuron-secreted MCP-1 and IL-9 to type 2 diabetes and Alzheimer's disease-associated metabolites

Type 2 diabetes (T2D) is implicated as a risk factor for Alzheimer's disease (AD), the most common form of dementia. In this work, we investigated neuroinflammatory responses of primary neurons to potentially circulating, blood-brain barrier (BBB) permeable metabolites associated with AD, T2D, or both. We identified nine metabolites associated with protective or detrimental properties of AD and T2D in literature (lauric acid, asparagine, fructose, arachidonic acid, aminoadipic acid, sorbitol, retinol, tryptophan, niacinamide) and stimulated primary mouse neuron cultures with each metabolite before quantifying cytokine secretion via Luminex. We employed unsupervised clustering, inferential statistics, and partial least squares discriminant analysis to identify relationships between cytokine concentration and disease-associations of metabolites. We identified MCP-1, a cytokine associated with monocyte recruitment, as differentially abundant between neurons stimulated by metabolites associated with protective and detrimental properties of AD and T2D. We also identified IL-9, a cytokine that promotes mast cell growth, to be differentially associated with T2D. Indeed, cytokines, such as MCP-1 and IL-9, released from neurons in response to BBB-permeable metabolites associated with T2D may contribute to AD development by downstream effects of neuroinflammation.

Ketohexokinase-dependent metabolism of cerebral endogenous fructose in microglia drives diabetes-associated cognitive dysfunction

Dementia, as an advanced diabetes-associated cognitive dysfunction (DACD), has become the second leading cause of death among diabetes patients. Given that little guidance is currently available to address the DACD process, it is imperative to understand the underlying mechanisms and screen out specific therapeutic targets. The excessive endogenous fructose produced under high glucose conditions can lead to metabolic syndrome and peripheral organ damage. Although generated by the brain, the role of endogenous fructose in the exacerbation of cognitive dysfunction is still unclear. Here, we performed a comprehensive study on leptin receptor-deficient T2DM mice and their littermate m/m mice and revealed that 24-week-old db/db mice had cognitive dysfunction and excessive endogenous fructose metabolism in the hippocampus by multiomics analysis and further experimental validation. We found that the rate-limiting enzyme of fructose metabolism, ketohexokinase, is primarily localized in microglia. It is upregulated in the hippocampus of db/db mice, which enhances mitochondrial damage and reactive oxygen species production by promoting nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4) expression and mitochondrial translocation. Inhibiting fructose metabolism via ketohexokinase depletion reduces microglial activation, leading to the restoration of mitochondrial homeostasis, recovery of structural synaptic plasticity, improvement of CA1 pyramidal neuron electrophysiology and alleviation of cognitive dysfunction. Our findings demonstrated that enhanced endogenous fructose metabolism in microglia plays a dominant role in diabetes-associated cognitive dysfunction and could become a potential target for DACD.

Sweet taste preference is associated with greater hypothalamic response to glucose and longitudinal weight gain

The hypothalamus has an abundant expression of sweet taste receptors that play a role in glucose sensing and energy homeostasis. Evidence suggests that liking "sweets" can be associated with weight gain, but the relationship between sweet taste preference and hypothalamic regulation of appetite is unknown. This study tested the hypothesis that sweet taste preference is associated with increased hypothalamic activation in response to glucose (a purported neural marker for weight gain risk) and greater longitudinal increases in body mass index (BMI). Fifty-four adults aged 18-35 years with a mean (± SD) BMI of 27.99 ± 5.32 kg/m2 completed the study. Height and weight were measured at baseline and 6-12 months later in a subset of 36 participants. Sweet taste preference was assessed via the Monell 2-series, forced-choice tracking procedure. Arterial spin labeling magnetic resonance imaging was performed before and after oral glucose ingestion to determine hypothalamic blood flow response to glucose. Linear models were used to examine relationships between sweet taste preference and the hypothalamic response to glucose and longitudinal changes in BMI, adjusting for age, sex, and baseline BMI. Sweet taste preference was positively associated with glucose-linked hypothalamic blood flow (beta = 0.017, p = 0.043), adjusted for age, sex and BMI. We also observed a positive association between sweet taste preference and longitudinal change in BMI (beta = 0.088, p = 0.015), adjusted for age, sex and baseline BMI. These findings suggest that heightened sweet taste preference is associated with glucose-linked hypothalamic activation and may be linked to increased susceptibility for weight gain.

The fructose survival hypothesis for obesity

The fructose survival hypothesis proposes that obesity and metabolic disorders may have developed from over-stimulation of an evolutionary-based biologic response (survival switch) that aims to protect animals in advance of crisis. The response is characterized by hunger, thirst, foraging, weight gain, fat accumulation, insulin resistance, systemic inflammation and increased blood pressure. The process is initiated by the ingestion of fructose or by stimulating endogenous fructose production via the polyol pathway. Unlike other nutrients, fructose reduces the active energy (adenosine triphosphate) in the cell, while blocking its regeneration from fat stores. This is mediated by intracellular uric acid, mitochondrial oxidative stress, the inhibition of AMP kinase and stimulation of vasopressin. Mitochondrial oxidative phosphorylation is suppressed, and glycolysis stimulated. While this response is aimed to be modest and short-lived, the response in humans is exaggerated due to gain of 'thrifty genes' coupled with a western diet rich in foods that contain or generate fructose. We propose excessive fructose metabolism not only explains obesity but the epidemics of diabetes, hypertension, non-alcoholic fatty liver disease, obesity-associated cancers, vascular and Alzheimer's dementia, and even ageing. Moreover, the hypothesis unites current hypotheses on obesity. Reducing activation and/or blocking this pathway and stimulating mitochondrial regeneration may benefit health-span. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.

Brain Dopamine-Clock Interactions Regulate Cardiometabolic Physiology: Mechanisms of the Observed Cardioprotective Effects of Circadian-Timed Bromocriptine-QR Therapy in Type 2 Diabetes Subjects

Despite enormous global efforts within clinical research and medical practice to reduce cardiovascular disease(s) (CVD), it still remains the leading cause of death worldwide. While genetic factors clearly contribute to CVD etiology, the preponderance of epidemiological data indicate that a major common denominator among diverse ethnic populations from around the world contributing to CVD is the composite of Western lifestyle cofactors, particularly Western diets (high saturated fat/simple sugar [particularly high fructose and sucrose and to a lesser extent glucose] diets), psychosocial stress, depression, and altered sleep/wake architecture. Such Western lifestyle cofactors are potent drivers for the increased risk of metabolic syndrome and its attendant downstream CVD. The central nervous system (CNS) evolved to respond to and anticipate changes in the external (and internal) environment to adapt survival mechanisms to perceived stresses (challenges to normal biological function), including the aforementioned Western lifestyle cofactors. Within the CNS of vertebrates in the wild, the biological clock circuitry surveils the environment and has evolved mechanisms for the induction of the obese, insulin-resistant state as a survival mechanism against an anticipated ensuing season of low/no food availability. The peripheral tissues utilize fat as an energy source under muscle insulin resistance, while increased hepatic insulin resistance more readily supplies glucose to the brain. This neural clock function also orchestrates the reversal of the obese, insulin-resistant condition when the low food availability season ends. The circadian neural network that produces these seasonal shifts in metabolism is also responsive to Western lifestyle stressors that drive the CNS clock into survival mode. A major component of this natural or Western lifestyle stressor-induced CNS clock neurophysiological shift potentiating the obese, insulin-resistant state is a diminution of the circadian peak of dopaminergic input activity to the pacemaker clock center, suprachiasmatic nucleus. Pharmacologically preventing this loss of circadian peak dopaminergic activity both prevents and reverses existing metabolic syndrome in a wide variety of animal models of the disorder, including high fat-fed animals. Clinically, across a variety of different study designs, circadian-timed bromocriptine-QR (quick release) (a unique formulation of micronized bromocriptine-a dopamine D2 receptor agonist) therapy of type 2 diabetes subjects improved hyperglycemia, hyperlipidemia, hypertension, immune sterile inflammation, and/or adverse cardiovascular event rate. The present review details the seminal circadian science investigations delineating important roles for CNS circadian peak dopaminergic activity in the regulation of peripheral fuel metabolism and cardiovascular biology and also summarizes the clinical study findings of bromocriptine-QR therapy on cardiometabolic outcomes in type 2 diabetes subjects.

High concentrations of fructose cause brain damage in mice

Excessive fructose consumption is associated with the incidence of obesity and systemic inflammation, resulting in increased oxidative damage and failure to the function of brain structures. Thus, we hypothesized that fructose consumption will significantly increase inflammation, oxidative damage, and mitochondrial dysfunction in the mouse brain and, consequently, memory damage. The effects of different fructose concentrations on inflammatory and biochemical parameters in the mouse brain were evaluated. Male Swiss mice were randomized into four groups: control, with exclusive water intake, 5%, 10%, and 20% fructose group. The 10% and 20% fructose groups showed an increase in epididymal fat, in addition to higher food consumption. Inflammatory markers were increased in epididymal fat and in some brain structures. In the evaluation of oxidative damage, it was possible to observe significant increases in the hypothalamus, prefrontal cortex, and hippocampus. In the epididymal fat and in the prefrontal cortex, there was a decrease in the activity of the mitochondrial respiratory chain complexes and an increase in the striatum. Furthermore, short memory was impaired in the 10% and 20% groups but not long memory. In conclusion, excess fructose consumption can cause fat accumulation, inflammation, oxidative damage, and mitochondrial dysfunction, which can damage brain structures and consequently memory.

How gut hormones shape reward: A systematic review of the role of ghrelin and GLP-1 in human fMRI

The gastrointestinal hormones ghrelin and glucagon-like peptide-1 (GLP-1) have opposite secretion patterns, as well as opposite effects on metabolism and food intake. Beyond their role in energy homeostasis, gastrointestinal hormones have also been suggested to modulate the reward system. However, the potential of ghrelin and GLP-1 to modulate reward responses in humans has not been systematically reviewed before. To evaluate the convergence of published results, we first conduct a multi-level kernel density meta-analysis of studies reporting a positive association of ghrelin (N_comb = 353, 18 contrasts) and a negative association of GLP-1 (N_comb = 258, 12 contrasts) and reward responses measured using task functional magnetic resonance imaging (fMRI). Second, we complement the meta-analysis using a systematic literature review, focusing on distinct reward phases and applications in clinical populations that may account for variability across studies. In line with preclinical research, we find that ghrelin increases reward responses across studies in key nodes of the motivational circuit, such as the nucleus accumbens, pallidum, putamen, substantia nigra, ventral tegmental area, and the dorsal mid insula. In contrast, for GLP-1, we did not find sufficient convergence in support of reduced reward responses. Instead, our systematic review identifies potential differences of GLP-1 on anticipatory versus consummatory reward responses. Based on a systematic synthesis of available findings, we conclude that there is considerable support for the neuromodulatory potential of gut-based circulating peptides on reward responses. To unlock their potential for clinical applications, it may be useful for future studies to move beyond anticipated rewards to cover other reward facets.

Hypothalamic Reactivity and Connectivity following Intravenous Glucose Administration

Dysfunctional glucose sensing in homeostatic brain regions such as the hypothalamus is interlinked with the pathogenesis of obesity and type 2 diabetes mellitus. However, the physiology and pathophysiology of glucose sensing and neuronal homeostatic regulation remain insufficiently understood. To provide a better understanding of glucose signaling to the brain, we assessed the responsivity of the hypothalamus (i.e., the core region of homeostatic control) and its interaction with mesocorticolimbic brain regions in 31 normal-weight, healthy participants. We employed a single-blind, randomized, crossover design of the intravenous infusion of glucose and saline during fMRI. This approach allows to investigate glucose signaling independent of digestive processes. Hypothalamic reactivity and connectivity were assessed using a pseudo-pharmacological design and a glycemia-dependent functional connectivity analysis, respectively. In line with previous studies, we observed a hypothalamic response to glucose infusion which was negatively related to fasting insulin levels. The observed effect size was smaller than in previous studies employing oral or intragastric administration of glucose, demonstrating the important role of the digestive process in homeostatic signaling. Finally, we were able to observe hypothalamic connectivity with reward-related brain regions. Given the small amount of glucose employed, this points toward a high responsiveness of these regions to even a small energy stimulus in healthy individuals. Our study highlights the intricate relationship between homeostatic and reward-related systems and their pronounced sensitivity to subtle changes in glycemia.

Early life exposure to high fructose diet induces metabolic dysregulation associated with sex-specific cognitive impairment in adolescent rats

The incidence of adolescent mental health disorders is on the rise. Epidemiological studies suggest that poor nutrition is a significant contributor to this public health crisis, specifically through exposure to high level of dietary sugar, including fructose, during critical periods of development. Previous studies have shown that elevated fructose exposure during adolescence disrupts mental health. Despite these data, it is currently unknown how fructose exposure, specifically during infancy, may impact adolescent mental health. We developed a rat experimental protocol to investigate the effects of fructose exposure during infancy on behavioral, cognitive and metabolic endpoints in adolescence. We found that exposing rats to high fructose from birth to weaning resulted in higher circulating glucose, insulin and leptin levels in adolescence. High fructose during infancy also increased bodyweight, disrupted metabolic homeostasis in the basolateral amygdala (BLA) as indicated by decreased activity of the cellular energy sensor AMPK, and impaired attention and impulsivity in a male-specific manner. This impaired attention observed in adolescent male rats following neonatal fructose exposure was partially rescued by viral-mediated, in vivo expression of a constitutively active form of AMPK in principal neurons of the BLA. Our results suggest that exposure to high level of fructose during infancy may impact adolescent mental health in a male-specific manner and that manipulation of AMPK activity may mitigate this impact.

Could Alzheimer's disease be a maladaptation of an evolutionary survival pathway mediated by intracerebral fructose and uric acid metabolism?

An important aspect of survival is to assure enough food, water, and oxygen. Here, we describe a recently discovered response that favors survival in times of scarcity, and it is initiated by either ingestion or production of fructose. Unlike glucose, which is a source for immediate energy needs, fructose metabolism results in an orchestrated response to encourage food and water intake, reduce resting metabolism, stimulate fat and glycogen accumulation, and induce insulin resistance as a means to reduce metabolism and preserve glucose supply for the brain. How this survival mechanism affects brain metabolism, which in a resting human amounts to 20% of the overall energy demand, is only beginning to be understood. Here, we review and extend a previous hypothesis that this survival mechanism has a major role in the development of Alzheimer's disease and may account for many of the early features, including cerebral glucose hypometabolism, mitochondrial dysfunction, and neuroinflammation. We propose that the pathway can be engaged in multiple ways, including diets high in sugar, high glycemic carbohydrates, and salt. In summary, we propose that Alzheimer's disease may be the consequence of a maladaptation to an evolutionary-based survival pathway and what had served to enhance survival acutely becomes injurious when engaged for extensive periods. Although more studies are needed on the role of fructose metabolism and its metabolite, uric acid, in Alzheimer's disease, we suggest that both dietary and pharmacologic trials to reduce fructose exposure or block fructose metabolism should be performed to determine whether there is potential benefit in the prevention, management, or treatment of this disease.

New insight on the mechanism of eating disorder in females based on metabolic differences of bisphenol S in female and male zebrafish

The different capacity of glucuronic acid metabolism might lead to the difference of bisphenol S (BPS) residual in tissues of male and female zebrafish. This may be the fundamental reason why BPS causes different effects in females and males. Here, adult zebrafish are exposed to 1, 10 and 100 μg/L BPS for 35 days to explore the main effect on females. After exposure, the liver of females showed stronger BPS metabolism ability than males, resulting in the accumulation of BPS in the gut of females. The results of neurotransmitters in gut of females revealed that the content of serotonin was decreased by BPS treatments. In addition, the mRNA expression levels of tryptophan 5-monooxygenase (Tph1) that regulated serotonin synthesis was reduced in gut of females in all BPS groups, and Tph1 protein has very high affinity with BPS molecule. Adult females treated with BPS exhibited symptoms including overeating, a decrease of serotonin in the gut, hypoglycemia and hyperlipidemia, a similar effect of Tph1 protein inhibitor LP533401 on adult females. This hypoglycemia stimulates brain agrp/pomc and orexin neurons to induce overfeeding behavior, causing intestinal homeostasis imbalance and hyperlipidemia. Our data elucidate a potential pathogenesis of eating disorder under pollutant stress.

Cerebral vascular function following the acute consumption of caffeinated artificially- and sugar sweetened soft drinks in healthy adults

Chronic consumption of sugar- and artificially-sweetened beverages (SSB and ASB) are associated with an increased risk of stroke but it is unclear how acute consumption influences cerebral vascular function. Purpose: We hypothesized that: (1) acute consumption of SSB and ASB would augment dynamic cerebral autoregulation (dCA) and attenuate cerebral vascular reactivity to hypercapnia (CVR_CO2) compared to water; and (2) dCA and CVR_CO2 would be attenuated with SSB compared to ASB and water. Methods: Twelve healthy adults (age: 23 ± 2 years, four females) completed three randomized trials where they drank 500 ml of water, SSB (Mountain Dew^®), or ASB (Diet Mountain Dew^®). We measured mean arterial pressure (MAP), middle and posterior cerebral artery blood velocities (MCAv and PCAv), and end-tidal CO₂ tension (PETCO₂). Cerebral vascular conductance was calculated as cerebral artery blood velocity/MAP (MCAc and PCAc). Twenty min after consumption, participants completed a 5 min baseline, and in a counterbalanced order, a CVR_CO2 test (3%, 5%, and 7% CO₂ in 3 min stages) and a dCA test (squat-stand tests at 0.10 Hz and 0.05 Hz for 5 min each) separated by 10 min. CVR_CO2 was calculated as the slope of the linear regression lines of MCAv and PCAv vs. PETCO₂. dCA was assessed in the MCA using transfer function analysis. Coherence, gain, and phase were determined in the low frequency (LF; 0.07-0.2 Hz) and very low frequency (VLF; 0.02-0.07 Hz). Results: MCAv and MCAc were lower after SSB (54.11 ± 12.28 cm/s, 0.58 ± 0.15 cm/s/mmHg) and ASB (51.07 ± 9.35 cm/s, 0.52 ± 1.0 cm/s/mmHg) vs. water (62.73 ± 12.96 cm/s, 0.67 ± 0.11 cm/s/mmHg; all P < 0.035), respectively. PCAc was also lower with the ASB compared to water (P = 0.007). MCA CVR_CO2 was lower following ASB (1.55 ± 0.38 cm/s/mmHg) vs. water (2.00 ± 0.57 cm/s/mmHg; P = 0.011) but not after SSB (1.90 ± 0.67 cm/s/mmHg; P = 0.593). PCA CVR_CO2 did not differ between beverages (P > 0.853). There were no differences between beverages for coherence (P ≥ 0.295), gain (P ≥ 0.058), or phase (P ≥ 0.084) for either frequency. Discussion: Acute consumption of caffeinated SSB and ASB resulted in lower intracranial artery blood velocity and conductance but had a minimal effect on cerebral vascular function as only MCA CVR_CO2 was altered with the ASB compared to water.

Nutrient infusion evoked magnetic resonance imaging signal in the human hypothalamus

BACKGROUND

The hypothalamus receives ingested nutrient information via ascending gut-related projections and plays a significant role in the regulation of food intake. Human neuroimaging studies have observed changes in the activity or connectivity of the hypothalamus in response to nutrient ingestion. However, previous neuroimaging studies have not yet assessed differences in temporal changes of hypothalamic responses to various nutrients in humans. Thus a repeated measures functional magnetic resonance imaging (fMRI) study using 30-min scans was designed to examine differences in hypothalamic responses to various nutrients.

METHODS

In this study, 18 healthy adults (mean age, 22.4 years; standard deviation, 4.8; age range, 19-39 years; 11 males and seven females) underwent fMRI sessions. On the day of each session, one of the four solutions (200 ml of monosodium glutamate, glucose, safflower oil emulsion, or saline) was administered to participants while fMRI scanning.

RESULTS

Infused amino acid and glucose, but not lipid emulsion, increased lateral hypothalamic responses as compared to a saline infusion ([x, y, z] = [4, -4, -10], z = 2.96). In addition, only hypothalamic responses to saline, but not those to the infusion of other nutrients, elicited a subjective sensation of hunger.

CONCLUSION

These findings suggest that lateral hypothalamic responses to ingested nutrients may mediate homeostatic sensations in humans.

Hypothalamic interaction with reward-related regions during subjective evaluation of foods

The reward system implemented in the midbrain, ventral striatum, orbitofrontal cortex, and ventromedial prefrontal cortex evaluates and compares various types of rewards given to the organisms. It has been suggested that autonomic factors influence reward-related processing via the hypothalamus, but how the hypothalamus modulates the reward system remains elusive. In this functional magnetic resonance imaging study, the hypothalamus was parcellated into individual hypothalamic nuclei performing different autonomic functions using boundary mapping parcellation analyses. The effective interaction during subjective evaluation of foods in a reward task was then investigated between the human hypothalamic nuclei and the reward-related regions. We found significant brain activity decrease in the paraventricular nucleus (PVH) and lateral nucleus in the hypothalamus in food evaluation compared with monetary evaluation. A psychophysiological interaction analysis revealed dual interactions between the PVH and (1) midbrain region and (2) ventromedial prefrontal cortex, with the former correlated with the stronger tendency of participants toward food-seeking. A dynamic causal modeling analysis further revealed unidirectional interactions from the PVH to the midbrain and ventromedial prefrontal cortex. These results suggest that the PVH in the human hypothalamus interacts with the reward-related regions in the cerebral cortex via multiple pathways (i.e., the midbrain pathway and ventromedial prefrontal pathway) to evaluate rewards for subsequent decision-making.

Comparison of oral administration of fructose and glucose on food intake and physiological parameters in broiler chicks

Like glucose, fructose is a monosaccharide, but the mechanisms of its absorption and metabolism in the body are very different between the 2 molecules. In this study, we investigated the effects of oral administration of glucose and fructose on food intake, diencephalic gene expression, and plasma metabolite concentrations in broiler chicks. The animals used in this study were 4-day-old male broiler chicks (Ross 308). They were given glucose, fructose (200 mg/ 0.5 mL/ bird), or a similar volume of distilled water orally after 6 h fasting. After treatment, measurements of food intake (at 0, 30, and 60 min), and blood glucose as well as insulin concentrations were measured over time; however, diencephalic (hypothalamus) gene expression and plasma metabolites were measured at 30 min. The results showed that glucose administration suppressed food intake, but fructose administration did not suppress food intake and it was at the same level as distilled water administration. In addition, fructose administration did not increase plasma glucose and insulin levels as did glucose administration. In the diencephalon, expression levels of genes related to the melanocortin system were unaffected by the treatment, while gene expression levels related to intracellular energy regulation, such as AMP-activated protein kinase were affected by the glucose treatment in the fasted chicks. These results suggest that fructose administration does not suppress feeding behavior as a result of possible reduction in the energy levels in the diencephalon and associated energy metabolism.

The development of the Metabolic-associated Fatty Liver Disease during pharmacotherapy of mental disorders - a review

Introduction: Metabolic-associated Fatty Liver Disease (MAFLD) is a term for Non-alcoholic Fatty Liver Disease (NAFLD) that highlights its association with components of the Metabolic Syndrome (MetS). MAFLD is becoming a clinically significant problem due to its increasing role in the pathogenesis of cryptogenic cirrhosis of the liver.

Material and methods: The resulting work is a review of the most important information on the risk of MAFLD development in the context of the use of particular groups of psychotropic drugs. The study presents the epidemiology, with particular emphasis on the population of psychiatric patients, pathophysiology and scientific reports analyzing the effect of the psychotropic medications on MAFLD development.

Results: The drugs that can have the greatest impact on the development of MAFLD are atypical antipsychotics, especially olanzapine, and mood stabilizers (MS) - valproic acid (VPA). Their effect is indirect, mainly through dysregulation of organism’s carbohydrate and lipid metabolism.

Conclusions: The population of psychiatric patients is particularly vulnerable to the development of MAFLD. At the root of this disorder lies the specificity of mental disorders, improper dietary habits, low level of physical activity and tendency to addictions. Also, the negative impact of the psychotropic drugs on the systemic metabolism indirectly contributes to the development of MAFLD. In order to prevent fatty liver disease, it is necessary to monitor metabolic and liver parameters regularly, and patients should be screened by ultrasound examination of the liver. There are also important preventive actions from the medical professionals, including education of patients and sensitizing to healthy lifestyle.

The effect of hunger state on hypothalamic functional connectivity in response to food cues

The neural underpinnings of the integration of internal and external cues that reflect nutritional status are poorly understood in humans. The hypothalamus is a key integrative area involved in short- and long-term energy intake regulation. Hence, we examined the effect of hunger state on the hypothalamus network using functional magnetic resonance imaging. In a multicenter study, participants performed a food cue viewing task either fasted or sated on two separate days. We evaluated hypothalamic functional connectivity (FC) using psychophysiological interactions during high versus low caloric food cue viewing in 107 adults (divided into four groups based on age and body mass index [BMI]; age range 24-76 years; BMI range 19.5-41.5 kg/m² ). In the sated compared to the fasted condition, the hypothalamus showed significantly higher FC with the bilateral caudate, the left insula and parts of the left inferior frontal cortex. Interestingly, we observed a significant interaction between hunger state and BMI group in the dorsolateral prefrontal cortex (DLPFC). Participants with normal weight compared to overweight and obesity showed higher FC between the hypothalamus and DLPFC in the fasted condition. The current study showed that task-based FC of the hypothalamus can be modulated by internal (hunger state) and external cues (i.e., food cues with varying caloric content) with a general enhanced communication in the sated state and obesity-associated differences in hypothalamus to DLPFC communication. This could potentially promote overeating in persons with obesity.

Acute inorganic nitrate intake increases regional insulin action in the brain: Results of a double-blind, randomized, controlled cross-over trial with abdominally obese men

AIMS

Improving brain insulin sensitivity may be a promising approach in the prevention and treatment of metabolic and cognitive diseases. Our aim was to investigate acute effects of inorganic nitrate on regional cerebral blood flow (CBF) responses to intranasal insulin in abdominally obese men.

METHODS

Eighteen apparently healthy men, aged 18-60 years and with a waist circumference ≥ 102 cm, participated in a randomized, double-blind, placebo-controlled cross-over trial. The study consisted of two test days separated by at least one week. Men received in random order a drink providing 10 mmol (i.e., 625 mg nitrate) potassium nitrate or an isomolar placebo drink with potassium chloride. Brain insulin action was assessed 120-150 min after the drinks by quantifying acute effects of nasal insulin on regional CBF using arterial spin labeling Magnetic Resonance Imaging. Glucose and insulin concentrations were measured at regular intervals, while blood pressure was determined fasted and at 240 min.

RESULTS

Inorganic nitrate intake increased regional insulin action in five brain clusters. The two largest clusters were located in the right temporal lobe (ΔCBF: 7.0 ± 3.8 mL/100 g/min, volume: 5296 mm³, P < 0.001; and ΔCBF: 6.5 ± 4.3 mL/100 g/min, volume: 3592 mm³, P < 0.001), while two other cortical clusters were part of the right frontal (ΔCBF: 9.0 ± 6.0 mL/100 g/min, volume: 1096 mm³, P = 0.007) and the left parietal lobe (ΔCBF: 6.1 ± 4.3 mL/100 g/min, volume: 1024 mm³, P = 0.012). One subcortical cluster was located in the striatum (ΔCBF: 5.9 ± 3.2 mL/100 g/min, volume: 1792 mm³, P < 0.001). No effects of nitrate were observed on CBF before administration. Following nitrate intake, circulating nitrate plus nitrite concentrations increased over time (P = 0.003), but insulin and glucose concentrations and blood pressure did not change.

CONCLUSION

Acute inorganic nitrate intake may improve regional brain insulin action in abdominally obese men. These regions are involved in the regulation of different metabolic and cognitive processes. The trial was registered on January 6th, 2021 at ClinicalTrials.gov as NCT04700241.

FGF21 response to sucrose is associated with BMI and dorsal striatal signaling in humans

OBJECTIVE

This study examined associations between BMI and dietary sugar intake with sucrose-induced fibroblast growth factor 21 (FGF21) and whether circulating FGF21 is associated with brain signaling following sucrose ingestion in humans.

METHODS

A total of 68 adults (29 male; mean [SD), age 23.2 [3.8] years; BMI 27.1 [4.9] kg/m² ) attended visits after a 12-hour fast. Plasma FGF21 was measured at baseline and at 15, 30, and 120 minutes after sucrose ingestion (75 g in 300 mL of water). Brain cerebral blood flow responses to sucrose were measured using arterial spin labeling magnetic resonance imaging.

RESULTS

Higher circulating FGF21 levels were associated with reduced blood flow in the striatum in response to sucrose (β = -7.63, p = 0.03). This association was greatest among persons with healthy weight (β = -15.70, p = 0.007) and was attenuated in people with overweight (β = -4.00, p = 0.63) and obesity (β = -12.45, p = 0.13). BMI was positively associated with FGF21 levels in response to sucrose (β = 0.53, p = 0.02). High versus low dietary sugar intake was associated with greater FGF21 responses to acute sucrose ingestion in individuals with healthy weight (β = 8.51, p = 0.04) but not in individuals with overweight or obesity (p > 0.05).

CONCLUSIONS

These correlative findings support evidence in animals showing that FGF21 acts on the brain to regulate sugar consumption through a negative feedback loop.

Mapping brain activity of gut-brain signaling to appetite and satiety in healthy adults: A systematic review and functional neuroimaging meta-analysis

Understanding how neurohormonal gut-brain signaling regulates appetite and satiety is vital for the development of therapies for obesity and altered eating behavior. However, reported brain areas associated with appetite or satiety regulators show inconsistency across functional neuroimaging studies. The aim of this study was to systematically assess the convergence of brain regions modulated by appetite and satiety regulators. Twenty-five studies were considered for qualitative synthesis, and 14 independent studies (20-experiments) found eligible for coordinate-based neuroimaging meta-analyses across 212 participants and 123 foci. We employed two different meta-analysis approaches. The results from the systematic review revealed the modulation of insula, amygdala, hippocampus, and orbitofrontal cortex (OFC) with appetite regulators, where satiety regulators were more associated with caudate nucleus, hypothalamus, thalamus, putamen, anterior cingulate cortex in addition to the insula and OFC. The two neuroimaging meta-analyses methods identified the caudate nucleus as a key area associated with satiety regulators. Our results provide quantitative brain activation maps of neurohormonal gut-brain signaling in heathy-weight adults that can be used to define alterations with eating behavior.

Integrative Hedonic and Homeostatic Food Intake Regulation by the Central Nervous System: Insights from Neuroimaging

Food intake regulation in humans is a complex process controlled by the dynamic interaction of homeostatic and hedonic systems. Homeostatic regulation is controlled by appetitive signals from the gut, adipose tissue, and the vagus nerve, while conscious and unconscious reward processes orchestrate hedonic regulation. On the one hand, sight, smell, taste, and texture perception deliver potent food-related feedback to the central nervous system (CNS) and influence brain areas related to food reward. On the other hand, macronutrient composition stimulates the release of appetite signals from the gut, which are translated in the CNS into unconscious reward processes. This multi-level regulation process of food intake shapes and regulates human ingestive behavior. Identifying the interface between hormones, neurotransmitters, and brain areas is critical to advance our understanding of conditions like obesity and develop better therapeutical interventions. Neuroimaging studies allow us to take a glance into the central nervous system (CNS) while these processes take place. This review focuses on the available neuroimaging evidence to describe this interaction between the homeostatic and hedonic components in human food intake regulation.

Acute effect of breaking up prolonged sitting on cognition: a systematic review

OBJECTIVES

To review the current evidence on the acute effects of interrupting prolonged periods of sitting with intermittent physical activity (PA) on cognition in healthy populations.

DESIGN

This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines.

METHODS

Studies were included if they investigated the acute effects of taking regular PA breaks from sitting on cognition in healthy populations without any cardiovascular disease, history of brain injury, or psychiatric or neurological disorder. Four electronic databases-PubMed, Scopus, MEDLINE and ProQuest-were searched for eligible studies on 20 September 2020. Study quality was assessed using the Physiotherapy Evidence Database scale.

RESULTS

Seven studies, involving 168 participants aged between 18 and 80 years, were eligible for inclusion in this review. Three of the seven studies found positive effects of interrupting sitting with either (a) 3 min of relatively high-intensity (6 km/hour) walking every 30 min on attention and inhibitory control in young adults; (b) hourly breaks with progressively longer duration (10-30 min) of very light-intensity cycling/walking on attention, working memory and cognitive flexibility in adults with obesity; or (c) an initial bout of continuous moderate-intensity exercise, followed by interruption of post-exercise sitting with 3 min breaks of light-intensity walking (3.2 km/hour) every 30 min, on working memory in older adults with overweight.

CONCLUSION

Given the limited evidence with mixed findings on this topic in the literature and the heterogeneity of PA protocols across the included studies, the results regarding the effectiveness of interrupting prolonged sitting with PA breaks in improving cognition warrant further verification.

PROSPERO REGISTRATION NUMBER

CRD42020147536.

Tolerable upper intake level for dietary sugars

Following a request from five European Nordic countries, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was tasked to provide scientific advice on a tolerable upper intake level (UL) or a safe level of intake for dietary (total/added/free) sugars based on available data on chronic metabolic diseases, pregnancy-related endpoints and dental caries. Specific sugar types (fructose) and sources of sugars were also addressed. The intake of dietary sugars is a well-established hazard in relation to dental caries in humans. Based on a systematic review of the literature, prospective cohort studies do not support a positive relationship between the intake of dietary sugars, in isocaloric exchange with other macronutrients, and any of the chronic metabolic diseases or pregnancy-related endpoints assessed. Based on randomised control trials on surrogate disease endpoints, there is evidence for a positive and causal relationship between the intake of added/free sugars and risk of some chronic metabolic diseases: The level of certainty is moderate for obesity and dyslipidaemia (> 50-75% probability), low for non-alcoholic fatty liver disease and type 2 diabetes (> 15-50% probability) and very low for hypertension (0-15% probability). Health effects of added vs. free sugars could not be compared. A level of sugars intake at which the risk of dental caries/chronic metabolic diseases is not increased could not be identified over the range of observed intakes, and thus, a UL or a safe level of intake could not be set. Based on available data and related uncertainties, the intake of added and free sugars should be as low as possible in the context of a nutritionally adequate diet. Decreasing the intake of added and free sugars would decrease the intake of total sugars to a similar extent. This opinion can assist EU Member States in setting national goals/recommendations.

Insight on Glucose and Fructose Absorption and Relevance in the Enterocyte Milieu

Although epidemiological studies indicate a strong correlation between high sugar intake and metabolic diseases, the biological mechanisms underlying this link are still controversial. To further examine the modification and crosstalk occurring in enterocyte metabolism during sugar absorption, in this study we evaluate the diffusion and intestinal metabolism of glucose, fructose and sucrose, which were supplemented in equimolar concentration to Caco-2 cells grown on polyester membrane inserts. At different time points after supplementation, changes in metabolite concentration were evaluated in the apical and basolateral chambers by nuclear magnetic resonance (NMR) and gas-chromatography (GC). Sucrose was only minimally hydrolyzed by Caco-2 cells. Upon supplementation, we observed a faster uptake of fructose than glucose, the pentose sugar being also faster catabolized. Monosaccharide absorption was concomitant to the synthesis/transport of other metabolites, which occurred differently in glucose and fructose supplemented cells. Our results confirm the prominent role of intestinal cells in fructose metabolism and clearance after absorption, representing a further step forward in the understanding of the role of dietary sugars. Future research, including targeted analysis on specific transporters/enzymes and the use of labeled substrates, will be helpful to confirm the present results and their interpretation.

Brain responses to glucose ingestion are greater in children than adults and are associated with overweight and obesity

OBJECTIVE

This study investigated whether brain regions involved in the regulation of food intake respond differently to glucose ingestion in children and adults and the relationship between brain responses and weight status.

METHODS

Data included 87 children (ages 7-11 years) and 94 adults (ages 18-35 years) from two cohorts. Healthy weight, overweight, and obesity were defined by Centers for Disease Control and Prevention criteria. Brain responses to glucose were determined by measuring cerebral blood flow using arterial spin labeling magnetic resonance imaging in brain regions involved in the regulation of eating behavior.

RESULTS

Children showed significantly larger increases in brain responses to glucose than adults in the dorsal striatum (p < 0.01), insula (p < 0.01), hippocampus (p < 0.01), and dorsal-lateral prefrontal cortex (p < 0.01). Responses to glucose in the dorsal striatum (odds ratio [OR] = 1.52, 95% CI 1.05-2.20; p = 0.03), hippocampus (OR = 1.51, 95% CI: 1.02-2.22; p = 0.04), insula (OR = 1.64, 95% CI: 1.11-2.42; p = 0.01), and orbitofrontal cortex (OR = 1.63 95% CI: 1.12-2.39; p = 0.01) were positively associated with overweight or obesity, independent of age group.

CONCLUSIONS

Children have greater brain responses to glucose ingestion than adults in regions involved in eating behavior, and these responses are associated with weight status.

The relationship between major food sources of fructose and cardiovascular disease, cancer, and all-cause mortality: a systematic review and dose-response meta-analysis of cohort studies

We aimed to summarize the associations between food sources of fructose and cardiovascular diseases (CVD), cancer, and all-cause mortality risk using a systematic review and meta-analysis. We searched PubMed, Scopus, and Web of Science up to November 2020. We included cohort studies that investigated the relationship between mortality risk (all-cause, CVD, specific CVD, and total and site-specific cancers) and intake of ≥1 food source of fructose (fruit, fruit juice, breakfast cereals, sugar-sweetened beverages (SSBs), sweets, and yogurt) in general adult population. Summary hazard ratios and 95% CIs were estimated using a random-effects model for linear and nonlinear relationships. Findings indicated that each 100 g/d increase in fruit intake was associated with 8-13% lower risk of CVDs, stroke, gastrointestinal, and lung cancer mortality. For all-cause mortality, there was a beneficial relationship up to 200 g/d fruit, and then plateaued. For ischemic heart disease and cancer mortality, there was a beneficial relationship up to 300 g/d followed by a slight increase. Ingestion of breakfast cereals and sweets was also associated with lower risk of all-cause mortality. For yogurt, a non-linear marginal decrease in all-cause mortality was found. Ingestion of each 200 g/d yogurt was associated with a 14% lower risk of CVD mortality. Every 60 g/d increase in sweet intake was linked to a 5% lower risk of all-cause mortality. Contrariwise, every 250 g/d increase in SSBs intake was associated with 7-10% higher risk of all-cause and CVD mortality. In conclusion, beneficial associations were found between fruit, breakfast cereals, sweets, and yogurt with all-cause and/or CVD mortality risk. Fruit intake had also an inverse link with cancer mortality. Conversely, SSBs had a harmful relationship with all-cause and CVD mortality.Registry number: CRD42019144956.

The interaction of lipids and inflammatory markers predict negative symptom severity in patients with schizophrenia

Finding biological predictors and novel mechanisms underlying negative symptoms of schizophrenia is of significant importance given the lack of effective treatments. Increasing data support a role for metabolic dysfunction and inflammation in reward processing deficits in psychiatric illness. Herein, we found an interaction between lipids and inflammation as a predictor of worse negative symptom severity in individuals with schizophrenia. Future studies may seek to further elucidate this relationship and thereby reveal novel treatment targets for negative symptoms.

Erythritol and xylitol differentially impact brain networks involved in appetite regulation in healthy volunteers

BACKGROUND

There is a growing consensus that sugar consumption should be reduced and the naturally occurring, low-calorie sweeteners xylitol and erythritol are gaining popularity as substitutes, but their effect on brain circuitry regulating appetite is unknown.

AIM

The study's objective was to examine the effects of the two sweeteners on cerebral blood flow (rCBF) and resting functional connectivity in brain networks involved in appetite regulation, and test whether these effects are related to gut hormone release.

METHODS

The study was performed as a randomized, double-blind, placebo-controlled, cross-over trial. Twenty volunteers received intragastric (ig) loads of 50g xylitol, 75g erythritol, 75g glucose dissolved in 300mL tap water or 300mL tap water. Resting perfusion and blood oxygenation level-dependent data were acquired to assess rCBF and functional connectivity. Blood samples were collected for determination of CCK, PYY, insulin and glucose.

RESULTS

We found: (i) xylitol, but not erythritol, increased rCBF in the hypothalamus, whereas glucose had the opposite effect; (ii) graph analysis of resting functional connectivity revealed a complex pattern of similarities and differences in brain network properties following xylitol, erythritol, and glucose; (iii) erythritol and xylitol induced a rise in CCK and PYY, (iv) erythritol had no and xylitol only minimal effects on glucose and insulin.

CONCLUSION

Xylitol and erythritol have a unique combination of properties: no calories, virtually no effect on glucose and insulin while promoting the release of gut hormones, and impacting appetite-regulating neurocircuitry consisting of both similarities and differences with glucose.

Diets Varying in Carbohydrate Content Differentially Alter Brain Activity in Homeostatic and Reward Regions in Adults

BACKGROUND

Obesity has one of the highest refractory rates of all chronic diseases, in part because weight loss induced by calorie restriction, the first-line treatment for obesity, elicits biological adaptations that promote weight regain. Although acute feeding trials suggest a role for macronutrient composition in modifying brain activity related to hunger and satiety, relevance of these findings to weight-loss maintenance has not been studied.

OBJECTIVES

We investigated effects of weight-loss maintenance diets varying in macronutrient content on regional cerebral blood flow (rCBF) in brain regions involved in hunger and reward.

METHODS

In conjunction with a randomized controlled feeding trial, we investigated the effects of weight-loss maintenance diets varying in carbohydrate content [high, 60% of total energy: n = 20; 6 men/14 women; mean age: 32.5 y; mean BMI (in kg/m 2): 27.4; moderate, 40% of total energy: n = 22; 10 men/12 women; mean age: 32.5 y; mean BMI: 29.0; low, 20% of total energy: n = 28; 12 men/16 women; mean age: 33.2 y; mean BMI: 27.7] on rCBF in brain regions involved in hunger and reward preprandial and 4 h postprandial after 14-20 wk on the diets. The primary outcome was rCBF in the nucleus accumbens (NAcc) at 4 h postprandial; the secondary outcome was preprandial rCBF in the hypothalamus.

RESULTS

Consistent with a priori hypothesis, at 4 h postprandial, NAcc rCBF was 43% higher in adults assigned to the high- compared with low-carbohydrate diet {P[family-wise error (FWE)-corrected] < 0.05}. Preprandial hypothalamus rCBF was 41% higher on high-carbohydrate diet [P(FWE-corrected) < 0.001]. Exploratory analyses revealed that elevated rCBF on high-carbohydrate diet was not specific to prandial state: preprandial NAcc rCBF [P(FWE-corrected) < 0.001] and 4 h postprandial rCBF in hypothalamus [P(FWE-corrected) < 0.001]. Insulin secretion predicted differential postprandial activation of the NAcc by diet.

CONCLUSIONS

We report significant differences in rCBF in adults assigned to diets varying in carbohydrate content for several months, which appear to be partially associated with insulin secretion. These findings suggest that chronic intake of a high-carbohydrate diet may affect brain reward and homeostatic activity in ways that could impede weight-loss maintenance. This trial was registered at clinicaltrials.gov as NCT02300857.

Neural mechanisms underlying the role of fructose in overfeeding

Fructose consumption has been linked with metabolic syndrome and obesity. Fructose-based sweeteners like high fructose corn syrup taste sweeter, improve food palatability, and are increasingly prevalent in our diet. The increase in fructose consumption precedes the rise in obesity and is a contributing driver to the obesity epidemic worldwide. The role of dietary fructose in obesity can be multifactorial by promoting visceral adiposity, hypertension, and insulin resistance. Interestingly, one emergent finding from human and animal studies is that dietary fructose promotes overfeeding. As the brain is a critical regulator of food intake, we reviewed the evidence that fructose can act in the brain and elucidated the major brain systems underlying fructose-induced overfeeding. We found that fructose acts on multiple interdependent brain systems to increase orexigenic drive and the incentive salience of food while decreasing the latency between food bouts and reducing cognitive control to disinhibit feeding. We concluded that the collective actions of fructose may promote feeding behavior by producing a hunger-like state in the brain.

Fructose and metabolic diseases: too much to be good

ABSTRACT

Excessive consumption of fructose, the sweetest of all naturally occurring carbohydrates, has been linked to worldwide epidemics of metabolic diseases in humans, and it is considered an independent risk factor for cardiovascular diseases. We provide an overview about the features of fructose metabolism, as well as potential mechanisms by which excessive fructose intake is associated with the pathogenesis of metabolic diseases both in humans and rodents. To accomplish this aim, we focus on illuminating the cellular and molecular mechanisms of fructose metabolism as well as its signaling effects on metabolic and cardiovascular homeostasis in health and disease, highlighting the role of carbohydrate-responsive element-binding protein in regulating fructose metabolism.

The effects of the form of sugar (solid vs. beverage) on body weight and fMRI activation: A randomized controlled pilot study

Objective

To test if sugar sweetened beverages (SSBs) and sugar sweetened solids (SSSs) have differential effects on body weight and reward processing in the brain.

Methods

In a single blind randomized controlled pilot trial (RCT), twenty participants with BMI between 20 and 40 kg/m² were randomized to consume a 20 fluid ounce soda (SSB, 248 kcal) or the equivalent in solid form (SSS; similar to thick gelatin or gummy candy) daily. At baseline and day 28, fasting body weight and fed-state BOLD fMRI of the brain were assessed. Differences in fMRI signals between views of low-fat (LF (<30%)) high sugar (HS (>30%)) food, and non-food images were calculated in brain regions implicated in energy homeostasis, taste, and reward.

Results

All participants in the SSB (6F 4M; 8 Caucasian; 36±14 y, 28.2±5.5 kg/m²; Mean±SD) and SSS (3F 7M; 6 Caucasian; 39±12; 26.3±4.4) groups completed the study. Weight change was 0.27±0.78 kg between SSB and SSS participants. Changes in the fMRI response to LF/HS foods in reward, homeostatic and taste regions tended to not be different between the groups over the four weeks. However, activation of the right substantia nigra increased following the SSB but decreased activation following the SSS in response to LF/HS foods over 28 days (-0.32±0.12). Ratings of wanting for LF/HS foods were correlated with activation in several brain regions, including the OFC.

Conclusions

Change in weight was modest between the groups in this study. Daily consumption of a SSB over 28 days led to mixed responses to LF/HS foods in areas of the brain associated with reward. Ratings of wanting are correlated with fMRI activation inside an MRI scanner.

Effect of Allopregnanolone on Spatial Memory and Synaptic Proteins in Animal Model of Metabolic Syndrome

Metabolic Syndrome (MetS) is considered a common disorder, especially with a sedentary lifestyle and unhealthy food consumption. Cognitive impairment is one of the MetS consequences that worsens the quality of life of the patients. The study aimed to assess the therapeutic effect of the neurosteroid Allopregnalonone on spatial memory and, therefore, the expression of two synaptic plasticity markers in the hippocampus. Thirty-two male rats were divided into four groups: control groups, MetS, and MetS + Allopregnalone. Spatial memory has been evaluated by the Y-maze task and blood pressure measured by the rat tail method. Biochemical evaluation of serum glucose, insulin, lipid profile, and hippocampal expression of Synaptophysin and Associated Protein 43 (GAP-43) were performed for assessing Allopregnanolone on serum and hippocampal markers. Allopregnanolone therapy improved working spatial memory, hypertension, and biochemical markers measured in the serum and hippocampus.

Chronic Fructose Substitution for Glucose or Sucrose in Food or Beverages and Metabolic Outcomes: An Updated Systematic Review and Meta-Analysis

Despite the publication of several of meta-analyses in recent years, the effects of fructose on human health remains a topic of debate. We previously undertook two meta-analyses on post-prandial and chronic responses to isoenergetic replacement of fructose for sucrose or glucose in food or beverages (Evans et al. 2017, AJCN 106:506–518 & 519–529). Here we report on the results of an updated search with a complete re-extraction of previously identified studies and a new and more detailed subgroup-analysis and meta-regression. We identified two studies that were published after our previous analyses, which slightly altered effect sizes and conclusions. Overall, the isoenergetic substitution of fructose for glucose resulted in a statistically significant but clinically irrelevant reduction in fasting blood glucose, insulin, and triglyceride concentrations. A subgroup analysis by diabetes status revealed much larger reductions in fasting blood glucose in people with impaired glucose tolerance and type 2 diabetes. However, each of these subgroups contained only a single study. In people with a healthy body mass index, fructose consumption was associated with statistically significant, but clinically irrelevant reductions in fasting blood glucose and fasting blood insulin. Meta-regression of the outcomes by a number of pre-identified and post-hoc covariates revealed some sources of heterogeneity, such as year of publication, age of the participants at baseline, and participants' sex. However, the small number of studies and the large number of potential covariates precluded detailed investigations of effect sizes in different subpopulations. For example, well-controlled, high quality studies in people with impaired glucose tolerance and type 2 diabetes are still lacking. Taken together, the available data suggest that chronic consumption of fructose is neither more beneficial, nor more harmful than equivalent doses of sucrose or glucose for glycemic and other metabolic outcomes.

Appetite-Regulating Hormones Are Reduced After Oral Sucrose vs Glucose: Influence of Obesity, Insulin Resistance, and Sex

CONTEXT

Fructose compared to glucose has adverse effects on metabolic function, but endocrine responses to oral sucrose vs glucose is not well understood.

OBJECTIVE

We investigated how oral sucrose vs glucose affected appetite-regulating hormones, and how biological factors (body mass index [BMI], insulin sensitivity, sex) influence endocrine responses to these 2 types of sugar.

DESIGN

Sixty-nine adults (29 men; 23.22 ± 3.74 years; BMI 27.03 ± 4.96 kg/m2) completed the study. On 2 occasions, participants consumed 300-mL drinks containing 75 g of glucose or sucrose. Blood was sampled at baseline, 10, 35, and 120 minutes post drink for plasma glucose, insulin, glucagon-like peptide (GLP-1)(7-36), peptide YY (PYY)total, and acyl-ghrelin measures. Hormone levels were compared between conditions using a linear mixed model. Interaction models were performed, and results were stratified to assess how biological factors influence endocrine responses.

RESULTS

Sucrose vs glucose ingestion provoked a less robust rise in glucose (P < .001), insulin (P < .001), GLP-1 (P < .001), and PYY (P = .02), whereas acyl-ghrelin suppression was similar between the sugars. We found BMI status by sugar interactions for glucose (P = .01) and PYY (P = .03); obese individuals had smaller increases in glucose and PYY levels after consuming sucrose vs glucose. There were interactions between insulin sensitivity and sugar for glucose (P = .003) and insulin (P = .04), and a sex by sugar interaction for GLP-1 (P = .01); men demonstrated smaller increases in GLP-1 in response to oral sucrose vs glucose.

CONCLUSION

Sucrose is less efficient at signaling postprandial satiation than glucose, and biological factors influence differential hormone responses to sucrose vs glucose consumption.

Low-Calorie Sweeteners with Carbohydrate Do Not Impair Insulin Sensitivity in Humans: Re-analysis Highlighting the Importance of the Comparator

The lack of appropriate comparator can lead to incorrect interpretation of results regarding low-calorie sweeteners. The result of a re-analysis of the study by Dalenberg et al. shows that the impairment of insulin sensitivity by sucralose in combination with carbohydrate may be explained by the carbohydrate component rather than the low-calorie sweetener.

Neuroimaging of hypothalamic mechanisms related to glucose metabolism in anorexia nervosa and obesity

BACKGROUNDGiven the heightened tolerance to self-starvation in anorexia nervosa (AN), a hypothalamic dysregulation of energy and glucose homeostasis has been hypothesized. Therefore, we investigated whether hypothalamic reactivity to glucose metabolism is impaired in AN.METHODSTwenty-four participants with AN, 28 normal-weight participants, and 24 healthy participants with obesity underwent 2 MRI sessions in a single-blind, randomized, case-controlled crossover study. We used an intragastric infusion of glucose and water to bypass the cephalic phase of food intake. The responsivity of the hypothalamus and the crosstalk of the hypothalamus with reward-related brain regions were investigated using high-resolution MRI.RESULTSNormal-weight control participants displayed the expected glucose-induced deactivation of hypothalamic activation, whereas patients with AN and participants with obesity showed blunted hypothalamic reactivity. Furthermore, patients with AN displayed blunted reactivity in the nucleus accumbens and amygdala. Compared with the normal-weight participants and control participants with obesity, the patients with AN failed to show functional connectivity between the hypothalamus and the reward-related brain regions during water infusion relative to glucose infusion. Finally, the patients with AN displayed typical baseline levels of peripheral appetite hormones during a negative energy balance.CONCLUSIONThese results indicate that blunted hypothalamic glucose reactivity might be related to the pathophysiology of AN. This study provides insights for future research, as it is an extended perspective of the traditional primary nonhomeostatic understanding of the disease.FUNDINGThis study was supported by a grant from the DFG (SI 2087/2-1).

Evidence of a Role for the Hippocampus in Food-Cue Processing and the Association with Body Weight and Dietary Added Sugar

OBJECTIVE

The current analysis used functional magnetic resonance imaging (fMRI) to explore a model of energy regulation postulating that the hippocampus integrates interoceptive signals and environmental stimuli to suppress responding to food cues. It was hypothesized that hippocampal activity would increase in response to food cues under postnutritive relative to fasted conditions, given the role of the hippocampus in integrating postnutritive signals with food cues, and that obesity, added sugar intake, or a combination of these factors would alter this response.

METHODS

Data were analyzed on 65 participants (29 males). Participants consumed drinks containing 75 g of glucose or water and underwent an fMRI-based food-cue task. Blood-oxygen-level-dependent (BOLD) fMRI was used to examine hippocampal responses to food and nonfood cues.

RESULTS

In lean participants, the hippocampal BOLD signal was higher following glucose compared with water, but participants with obesity showed the opposite pattern. BMI interacted with added sugar intake such that BMI was more negatively correlated with hippocampal food-cue reactivity after glucose ingestion in individuals who consumed high levels of added sugar. Hippocampal BOLD was negatively correlated with prospective food intake.

CONCLUSIONS

The findings are consistent with the view that energy regulation involves hippocampal processes in humans and that added sugar and excess weight may impair this function.

Dietary fructose as a model to explore the influence of peripheral metabolism on brain function and plasticity

High consumption of fructose has paralleled an explosion in metabolic disorders including obesity and type 2 diabetes. Even more problematic, sustained consumption of fructose is perceived as a threat for brain function and development of neurological disorders. The action of fructose on peripheral organs is an excellent model to understand how systemic physiology impacts the brain. Given the recognized action of fructose on liver metabolism, here we discuss mechanisms by which fructose can impact the brain by interacting with liver and other organs. The interaction between peripheral and central mechanisms is a suitable target to reduce the pathophysiological consequences of neurological disorders.

Resting-state functional connectivity of the human hypothalamus

Communication pathways of the hypothalamus with other brain regions and the periphery are critical to successfully control key physiological and psychological processes. With advanced functional magnetic resonance imaging (fMRI) techniques, it is possible to target hypothalamic function and infer discrete hypothalamus networks. Resting-state functional connectivity (RSFC) is a promising tool to study the functional organization of the brain and may act as a marker of individual differences and dysfunctions. Based on recent fMRI findings, the hypothalamus is mostly connected to parts of the striatum, midbrain, thalamus, insula, frontal, cingulate, and temporal cortices and the cerebellum. There is a strong interplay of the hypothalamus with these regions in response to different metabolic, hormonal, and nutritional states. In a state of hunger, hypothalamus RSFC increases with a strong shift to reward-related brain regions, especially in person with excessive weight. Nutrient signals and hormones, as insulin, act on these same connections conveying reward and internal signals to regulate homeostatic control. Moreover, dysfunctional hypothalamus communication has been documented in persons with neurological and psychiatric diseases. The results implicate that patients with depression, epilepsy, and neurodegenerative diseases show mostly a reduction in hypothalamus RSFC, whereas patients with migraine and headache display predominantly increased hypothalamus RSFC. The extent of these changes and regions affected depend on the disorder and symptom severity. Whether hypothalamus RSFC can serve as a marker for disease states or is a prodromal neurobiological feature still needs to be investigated.

Intranasal insulin administration decreases cerebral blood flow in cortico-limbic regions: A neuropharmacological imaging study in normal and overweight males

AIM

To assess and compare the effects of 160 IU intranasal insulin (IN-INS) administration on regional cerebral blood flow (rCBF) in healthy male individuals with normal weight and overweight phenotypes.

METHODS

Thirty young male participants (mean age 25.9 years) were recruited and stratified into two cohorts based on body mass index: normal weight (18.5-24.9 kg/m² ) and overweight (25.0-29.9 kg/m² ). On separate mornings participants received 160 IU of IN-INS using an intranasal protocol and intranasal placebo as part of a double-blind crossover design. Thirty minutes following administration rCBF data were collected using a magnetic resonance imaging method called pseudocontinuous arterial spin labelling. Blood samples were collected to assess insulin sensitivity and changes over time in peripheral glucose, insulin and C-peptide.

RESULTS

Insulin sensitivity did not significantly differ between groups. Compared with placebo, IN-INS administration reduced rCBF in parts of the hippocampus, insula, putamen, parahippocampal gyrus and fusiform gyrus in the overweight group. No effect was seen in the normal weight group. Insula rCBF was greater in the overweight group versus normal weight only under placebo conditions. Peripheral glucose and insulin levels were not affected by IN-INS. C-peptide levels in the normal weight group decreased significantly over time following IN-INS administration but not placebo.

CONCLUSION

Insulin-induced changes within key regions of the brain involved in gustation, memory and reward were observed in overweight healthy male individuals. Following placebo administration, differences in gustatory rCBF were observed between overweight and normal weight healthy individuals.

Glucose and fat sensing in the human hypothalamus

Energy balance is centrally regulated by the brain through several interacting neuronal systems involving external, peripheral, and central factors within the brain. The hypothalamus integrates these factors and is the key brain area in the regulation of energy balance. In this review, we will explain the structure of the hypothalamus and its role in the regulation of energy balance. An important part of energy balance regulation is the sensing of nutrient status and availability. This review will focus on the sensing of the two main sources of energy by the hypothalamus: glucose and fat. As many common health problems and chronic diseases can be traced back to a disrupted hypothalamic function, we will also discuss hypothalamic sensing of glucose and fats in these pathologies. Finally, we will summarize the current knowledge and discuss how this may be applied clinically and for future research perspectives.