Recent advances in the modification of taste and food preferences following bariatric surgery

The Neural Code for Taste in the Nucleus of the Solitary Tract of Rats with Obesity Following Roux-En-Y Gastric Bypass Surgery

Previous work has shown that taste responses in the nucleus tractus solitarius (NTS; the first central relay for gustation) are blunted in rats with diet-induced obesity (DIO). Here, we studied whether these effects could be reversed by Roux-en-Y gastric bypass (RYGB) surgery, an effective treatment for obesity. Rats were fed a high energy diet (60% kcal fat; HED) both before and after undergoing RYGB. Electrophysiological responses from NTS cells in unrestrained rats were recorded as they licked tastants from a lick spout. Sweet, salty, and umami tastes, as well as their naturalistic counterparts, were presented. Results were compared with those of lean rats from a previous study. As with DIO rats, NTS cells in RYGB rats were more narrowly tuned, showed weaker responses, and less lick coherence than those in lean rats. Both DIO and RYGB rats licked at a slower rate than lean rats and paused more often during a lick bout. However, unlike DIO rats, the proportion of taste cells in RYGB rats was similar to that in lean rats. Our data show that, despite being maintained on a HED after surgery, RYGB can induce a partial recovery of the deficits seen in the NTS of DIO rats.

Taste of Fat and Obesity: Different Hypotheses and Our Point of View

Obesity results from a temporary or prolonged positive energy balance due to an alteration in the homeostatic feedback of energy balance. Food, with its discriminative and hedonic qualities, is a key element of reward-based energy intake. An alteration in the brain reward system for highly palatable energy-rich foods, comprised of fat and carbohydrates, could be one of the main factors involved in the development of obesity by increasing the attractiveness and consumption of fat-rich foods. This would induce, in turn, a decrease in the taste of fat. A better understanding of the altered reward system in obesity may open the door to a new era for the diagnosis, management and treatment of this disease.

A systematic review and meta-analyses of food preference modifications after bariatric surgery

This systematic review and meta-analyses aimed to synthesize evidence of the link between bariatric surgery and changes in food preferences, considering the method of assessment. MEDLINE, Cochrane Library, Web of Science, Cinahl, PsychINFO, ProQuest, and Open grey were searched incorporating two blocks of terms ("Intervention" and "Food Preferences"). Interventional or observational studies involving patients (BMI ≥ 35 kg m^-2 ) with sleeve gastrectomy (SG) or Roux-en-Y Gastric Bypass (RYGB) and a control group were included. Meta-analyses were performed comparing the standardized daily mean percentage energy from proteins, carbohydrates, and lipids between preoperative and postoperative patients. Fifty-seven studies concerning 2,271 patients with RYGB and 903 patients with SG met the inclusion criteria, of which 24 were eligible for meta-analysis. Despite a total reduction in macronutrient intakes, the meta-analyses revealed a postoperative increase in percentage energy from proteins at 12 months (0.24, 95% CI: 0.03, 0.46, {I² } = 73%) and a decrease in percentage energy from fat at 1 month (-0.47, 95% CI: 0.86, 0.09, {I² } = 72%), up to 24 months (-0.20, 95% CI: -0.31, 0.08, {I² } = 0%). In conclusion, the present systematic review and meta-analyses showed changes of food preferences in terms of macronutrient, food selection and, overall food appreciation up to 5 years following bariatric surgery.

Mechanism of bariatric and metabolic surgery: beyond surgeons, gastroenterologists and endocrinologists

Bariatric-metabolic surgery is the safest, most effective and long-lasting treatment for obesity and its associated co-morbidities, whether they be metabolic (type 2 diabetes, hyperlipidemia non-alcoholic fatty liver disease) or cardiovascular (myocardial infarction, stroke). Due to the obesity pandemic, bariatric-metabolic surgery is the second most frequent intra-abdominal procedure and the gastroenterologist and the surgeon must be aware of the physiologic changes caused by the anatomic reconfiguration following surgery. Among the mechanisms of action, independent of the loss of weight and fat tissue, surgery leads to the release of gut hormones related to carbohydrate metabolism (the rapid and continuous release of insulin), appetite and degree of satiety (glucagon-like peptide 1, peptide Y-Y, grhelin). As a result, indications for surgery have been extended to earlier disease stages. Apart from the neurohormonal effects, changes in the metabolism of biliary acids and the microbiota have also been reported. The aim of this review is to describe the physiologic changes caused by bariatric-metabolic surgery.

Bariatric Surgical Alterations in Tolerability, Enjoyment and Cravings in the Diet (BSATED) instrument: A new scale to measure food preferences following bariatric surgery

Bariatric surgery is associated with changing food preferences, but it is not known whether these changes differ by type of operation or are associated with weight loss. The current study presents validation results for a new 27-item scale, Bariatric Surgical Alterations in Tolerability, Enjoyment and Cravings in the Diet (BSATED). This scale measured enjoyment, craving, and intolerance changes for nine food and beverage categories common to dietary habits in the Southern California region of the U.S. one year following bariatric surgery in the Bariatric Experience Long Term (BELONG) study. Validation of BSATED was done using exploratory factor analyses, construct validity with other conceptually related survey instruments, and criterion validity using hypothesized differences for operation type and percent total weight loss (%TWL) at 12-18 months after surgery. Participants (n = 999) were 86% female, 41% non-Hispanic White, with a mean age of 43.1 ± 11.3 years and a body mass index (BMI) of 43.4 ± 6.8 kg/m² at the time of surgery. Participants reported less enjoyment and craving for high-fat meats (62%), grains (54%), candy and other desserts (e.g. candy bars, chocolate, ice cream) (52%), and sweet baked goods (48%) 12 months after surgery. These changes were more common among participants undergoing Roux-en-Y gastric bypass (RYGB) compared to those receiving sleeve gastrectomy (SG). Participants who reported decreased enjoyment and craving for foods and beverages that post-bariatric patients are counseled to reduce or avoid had greater %TWL at 12-18 months following surgery (p < .001 and p = .003 respectively). The foods and beverages in BSATED that post-bariatric patients are counseled to reduce or avoid could be used to understand how changes in enjoyment, craving and tolerability of these foods/beverages contribute to weight loss following surgery.

Bariatric Surgery Leads to Short-Term Effects on Sweet Taste Sensitivity and Hedonic Evaluation of Fatty Food Stimuli

OBJECTIVE

The aim of this study was to investigate the effect of bariatric surgery on sweet taste sensitivity and the hedonic evaluation of sweet, savory, and fatty food stimuli as well as associations with weight loss and food preferences assessed at a buffet meal test.

METHODS

The detection and recognition threshold for sweet taste and the hedonic rating of sweet, savory, and fatty food stimuli were assessed before and after a preoperative diet-induced weight loss and 6 weeks, 6 months, and 18 months after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) (n = 29).

RESULTS

The detection threshold for sweet taste decreased after the diet-induced weight loss and 6 weeks after RYGB (both P ≤ 0.03). The hedonic rating of high-fat food stimuli decreased 6 weeks after RYGB and SG (all P ≤ 0.02). Changes in the hedonic rating of high-fat food stimuli were associated with increased preferences for high-fat foods at the buffet meal (P = 0.03) and tended to be associated with weight loss (P = 0.05). No changes were detected for sweet and savory food stimuli.

CONCLUSIONS

RYGB increased sweet taste sensitivity; however, this effect was already seen after the diet-induced weight-loss. RYGB and SG decreased the hedonic evaluation of high-fat food stimuli, but this effect did not translate into decreased preferences for high-fat food.

Associations between Weight Loss, Food Likes, Dietary Behaviors, and Chemosensory Function in Bariatric Surgery: A Case-Control Analysis in Women

We tested the hypothesis that successful weight loss post-bariatric surgery would be associated with healthier chemosensory function, food likes, and dietary behaviors than either unsuccessful weight loss or pre-surgery morbid obesity. In a case-control design, pre-surgical women with morbid obesity (n = 49) were compared with those 1-year post-surgery (24 Roux-en-Y Bypass, 24 Sleeve Gastrectomy) and defined by excess or percent weight loss as successful/unsuccessful. For self-reported smell/taste perception, more post-surgery than pre-surgery reported improved/distorted perception, especially if weight loss successful. Measured taste function (perceived quinine and NaCl intensity) was lower among weight loss unsuccessful versus pre-surgery patients, yet a genetic variation in taste probe (propylthiouracil bitterness) matched expected frequencies without significant pre/post-surgery difference. Regarding survey-reported liking, higher diet quality was seen in the weight loss successful (independent of surgery type) versus pre-surgical patients, with differences driven by lower sweet and refined carbohydrate liking. The post versus pre-surgical patients had greater restraint but less hunger and disinhibition. Patients reporting both higher diet quality and lower hunger showed greater % weight loss, independent of surgery type. Thus, successful weight loss 1-year post-bariatric surgery was associated with improved or distorted chemosensation and patterns of liking associated with healthier diets, especially if coupled with less hunger.

Regulation of Energy Homeostasis After Gastric Bypass Surgery

The obesity epidemic continues to escalate each year in the United States more than anywhere else in the world. The existing pharmaceutical and other nonsurgical treatments for morbid obesity produce suboptimal physiologic outcomes compared with those of Roux-en-Y gastric bypass (RYGB) surgery. RYGB has been the gold standard of bariatric surgery because the beneficial long-term outcomes, which include sustainable weight loss and type 2 diabetes mellitus (T2DM) resolution, are far superior to those obtained with other bariatric surgeries. However, the current understanding of RYGB's mechanisms of actions remains limited and incomplete. There is an urgent need to understand these mechanisms as gaining this knowledge may lead to the development of innovative and less invasive procedures and/or medical devices, which can mirror the favorable outcomes of RYGB surgery. In this review, we highlight current observations of the metabolic and physiologic events following RYGB, with a particular focus on the role of the anatomical reconfiguration of the gastrointestinal tract after RYGB.

Carbohydrate craving: not everything is sweet

PURPOSE OF REVIEW

Cravings for carbohydrates have been known about for hundreds of years but the mechanisms behind it were unclear. This review will highlight recent advances in our knowledge of mechanisms to detect carbohydrates in the diet.

RECENT FINDINGS

Recent work has begun to identify the physiological mechanisms by which carbohydrates and glucose are detected and how this drives their intake. Recently, evidence has been found for systems that regulate carbohydrate and glucose intake via taste, hedonic, and homeostatic pathways.

SUMMARY

Identification of the physiological mechanisms that regulate carbohydrate intake will allow a better understanding of how their intake is regulated and responds to changes in dietary intake. Such an understanding will be a key for developing a more rational approach to the development of successful weight loss diets.

Lingual CD36 and nutritional status differentially regulate fat preference in obesity-prone and obesity-resistant rats

Lingual fatty acid receptors (i.e. CD36) mediate the orosensory perception of fat/fatty acids and may contribute to the susceptibility to develop obesity. The current study tested the hypothesis that fat/fatty acid preference in obesity-prone (OP, Osborne-Mendel) and obesity-resistant (OR, S5B/Pl) rats is mediated by nutritional status and lingual CD36. To determine if nutritional status affected linoleic acid (LA) preference in OP and OR rats, rats were either fasted overnight or fed a high fat diet (60% kcal from fat). In OR rats, fasting increased the preference for higher concentrations of LA (1.0%), while consumption of a high fat diet decreased LA preference. In OP rats, fasting increased the preference for lower concentrations of LA (0.25%), however high fat diet consumption did not alter LA preference. To determine if lingual CD36 mediated the effects of an overnight fast on LA preference, the expression of lingual CD36 mRNA was assessed and the effect of lingual application of CD36 siRNA on LA preference was determined. Fasting increased lingual CD36 mRNA expression in OR rats, but failed to alter lingual CD36 mRNA in OP rats. Following an overnight fast, application of lingual CD36 siRNA led to a decrease in LA preference in OR, but not OP rats. Lingual application of CD36 siRNA was also used to determine if lingual CD36 mediated the intake and preference for a high fat diet in OP and OR rats. CD36 siRNA decreased the preference and intake of high fat diet in OR rats, but not OP rats. The results from this study suggest that the dysregulation of lingual CD36 in OP rats is a potential factor leading to increased fat intake and fat preference and an enhanced susceptibility to develop obesity.