Changes in appetite, taste, smell, and food aversion in post-bariatric patients and their relations with surgery time, weight loss and regain

Comment on Matsuo et al. Impact of Olfactory Change on Postoperative Body Weight Loss in Patients with Gastric Cancer after Gastrectomy. Nutrients 2024, 16, 851

I read with interest the paper by Matsuo et al [...].

Taste and odor interactions after metabolic surgery

Most patients report "taste" changes after undergoing metabolic surgeries. Yet, most studies that used validated sensory evaluation techniques, including ours, found no changes in perceived taste intensity from before to after surgery. However, we assessed participants with pure gustatory stimuli and after an overnight fast, which raises questions about whether patients' self-reported "taste" changes are due to conflating changes in retronasal smell/"flavor" with taste changes or whether they only manifest during the fed state. To investigate this, we conducted a cross-sectional study comparing sensory responses in women who underwent metabolic surgery 2 to 6 yr ago (n = 15) with 2 nonoperated control groups: one with a body mass index (BMI) equivalent (n = 15) and one with a healthy BMI (n = 15). Participants attended 2 sessions, one fed and one fasted. Using a sip-and-spit method, women tasted liquid samples containing gustatory and olfactory stimuli and puddings with varying fat content with and without nose clips. They used separate general labeled magnitude scales to rate their perceived intensity of taste, smell, flavor, and liking. Mixed ANOVAs indicated that the surgery and BMI equivalent groups rated retronasal smell intensity of coffee stronger than the healthy BMI group (P ≤ 0.015). However, there were no differences in taste/flavor intensity or liking ratings among groups. Additionally, feeding conditions did not significantly affect perceived intensity ratings. Our findings suggest that changes in the sensory-discriminatory component of taste or taste-odor interactions are not significant contributors to dietary modifications following metabolic surgery.

The Role of the Olfactory System in Obesity and Metabolism in Humans: A Systematic Review and Meta-Analysis

Obesity, linked to chronic diseases, poses a global health challenge. While the role of the olfactory system in energy homeostasis is well-documented in rodents, its role in metabolism regulation and obesity in humans remains understudied. This review examines the interplay between olfactory function and metabolic alterations in human obesity and the effects of bariatric surgery on olfactory capabilities in humans. Adhering to PRISMA guidelines, a systematic review and meta-analysis was conducted, focusing exclusively on original human studies. From 51 articles, 14 were selected for the meta-analysis. It was found that variations in olfactory receptor genes influence the susceptibility to odors and predisposition to weight gain and poor eating habits. Bariatric surgery, particularly sleeve gastrectomy, shows significant improvements in olfactory function (SMD 2.37, 95% CI [0.96, 3.77], I = 92%, p = 0.001), especially regarding the olfactory threshold (SMD -1.65, 95% CI [-3.03, -0.27], I = 81%, p = 0.02). There is a bidirectional relationship between olfactory function and metabolism in humans. Bariatric surgery improves olfactory perception in obese patients, but it is still unclear if impacting the olfactory system directly affects eating behavior and the energy balance. However, these findings open novel avenues for future studies addressing the olfactory system as a novel target to alter systemic metabolism in humans.

Microvascular Function, Inflammatory Status, and Oxidative Stress in Post-Bariatric Patients with Weight Regain

Weight loss after bariatric surgery in obesity improves vascular function and metabolic/inflammatory profiles and reduces cardiovascular mortality but there are limited data on the effects of weight regain on vascular health. We compared the metabolic/inflammatory profiles, oxidative status, and vascular function of post-bariatric patients with a high ratio of weight regain (RWR) vs. non-surgical controls. Thirty-two post-bariatric patients [Roux-en-Y gastric bypass; aged = 44 ± 8 years, BMI = 40.1 ± 7.7 kg/m², and RWR = 58.7 ± 24.3%] and thirty controls that were BMI-, age-, and gender-matched entered the study. We collected clinical data, metabolic/inflammatory/oxidative stress circulating biomarkers, and endothelial/microvascular reactivity through Venous occlusion plethysmography and Laser speckle contrast imaging. The bariatric group exhibited lower neck circumference, fasting glucose, and triglycerides than the non-surgical group, while HDL-cholesterol was higher in the bariatric group (p < 0.001). There was no significant difference between groups for endothelial/microvascular reactivities (p ≥ 0.06). Resistin, leptin, endothelin-1, soluble forms of intercellular cell adhesion molecule-1 and vascular cell adhesion molecule-1, tumor necrosis factor-α, and thiobarbituric acid reactive substances did not differ significantly between groups (p ≥ 0.09) either. The adiponectin level was higher in the bariatric compared to the non-surgical group, while interleukin-6 was lower in the bariatric group (p < 0.001). Despite the fact that endothelial/microvascular functions were not significantly different between groups, post-bariatric patients present partially preserved metabolic/inflammatory benefits even with high RWR.

Nutritional and Lifestyle Behaviors Reported Following One Anastomosis Gastric Bypass Based on a Multicenter Study

This study aimed to describe nutritional and lifestyle parameters following one-anastomosis gastric bypass (OAGB). A multicenter study among OAGB patients across Israel (n = 277) and Portugal (n = 111) was performed. Patients were approached according to the time elapsed since surgery. An online survey with information regarding demographics, anthropometrics, and nutritional and lifestyle aspects was administered in both countries simultaneously. Respondents from Israel (pre-surgery age of 41.6 ± 11.0 years, 75.8% females) and Portugal (pre-surgery age of 45.6 ± 12.3 years, 79.3% females) reported changes in their appetite (≤94.0% and ≤94.6%), changes in their taste (≤51.0 and ≤51.4%), and intolerance to specific foods (i.e., red meat, pasta, bread, and rice). Bariatric surgery-related eating recommendations were generally followed well, but a trend toward lower adherence was evident in groups with longer time elapsed since surgery in both countries. Most respondents from Israel and Portugal reported participation in follow-up meetings with a surgeon (≤94.0% and 100%) and a dietitian (≤92.6% and ≤100%), while far fewer reported participation in any follow-up meeting with a psychologist/social worker (≤37.9% and ≤56.1%). Patients following OAGB might experience changes in appetite, taste, and intolerance to specific foods. Adherence to bariatric surgery-related eating recommendations is not always satisfying, especially in the longer term post-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.

One-Year Self-Reported Appetite Is Similar in Adolescents with Obesity Who Do or Do Not Undergo Sleeve Gastrectomy

BACKGROUND

With the growing prevalence of severe obesity in adolescents, sleeve gastrectomy (SG), a type of metabolic bariatric surgery (MBS), is increasingly being performed at a younger age. Data regarding changes in homeostatic and hedonic appetite following SG are conflicting in adults, with some studies showing no change and others showing a decrease in appetite. Data evaluating the effect of SG on appetite during adolescence, when appetite is more plastic, are currently lacking.

OBJECTIVE

To evaluate appetite changes one year after SG in adolescents with obesity vs. in non-surgical controls (NS).

METHODS

Thirty-nine subjects 13-21 years old with severe obesity were followed for a year; 19 underwent SG, and 20 were followed without surgery. Subjects had fasting blood tests for appetite-regulating hormones and completed a visual analog scale for appetite assessment (VAS).

RESULTS

The SG group had a decrease in body mass index (BMI) at one-year (baseline: 48.2 ± 1.7 kg/m2; one-year follow-up: 42.6 ± 1.0 kg/m2 (p ≤ 0.0001)). No within- or between-group differences were noted in the one-year change in appetite in the SG and NS groups. After SG, fasting ghrelin decreased (p ≤ 0.0001); however, no changes were noted in peptide YY (PYY) levels. Changes in one homeostatic appetite measure following SG were inversely associated with changes in fasting PYY (r = -0.583, p = 0.011). Appetite changes were not associated with weight loss or final BMI.

CONCLUSIONS

There were no changes in appetite measures one-year after SG from pre-surgery levels in adolescents with obesity, and appetite changes were not associated with changes in BMI. It is important to evaluate the impact of long-term appetite changes, if any, on weight loss after SG.