Role of gut hormones in obesity

Altered gut and adipose tissue hormones in overweight and obese individuals: cause or consequence?

The aim of this article is to review the research into the main peripheral appetite signals altered in human obesity, together with their modifications after body weight loss with diet and exercise and after bariatric surgery, which may be relevant to strategies for obesity treatment. Body weight homeostasis involves the gut–brain axis, a complex and highly coordinated system of peripheral appetite hormones and centrally mediated neuronal regulation. The list of peripheral anorexigenic and orexigenic physiological factors in both animals and humans is intimidating and expanding, but anorexigenic glucagon-like peptide 1 (GLP-1), cholecystokinin (CCK), peptide YY (PYY) and orexigenic ghrelin from the gastrointestinal tract, pancreatic polypeptide (PP) from the pancreas and anorexigenic leptin from adiposites remain the most widely studied hormones. Homeostatic control of food intake occurs in humans, although its relative importance for eating behaviour is uncertain, compared with social and environmental influences. There are perturbations in the gut–brain axis in obese compared with lean individuals, as well as in weight-reduced obese individuals. Fasting and postprandial levels of gut hormones change when obese individuals lose weight, either with surgical or with dietary and/or exercise interventions. Diet-induced weight loss results in long-term changes in appetite gut hormones, postulated to favour increased appetite and weight regain while exercise programmes modify responses in a direction expected to enhance satiety and permit weight loss and/or maintenance. Sustained weight loss achieved by bariatric surgery may in part be mediated via favourable changes to gut hormones. Future work will be necessary to fully elucidate the role of each element of the axis, and whether modifying these signals can reduce the risk of obesity.

Circulating glucagon-like peptide-1 increases in response to short-term overfeeding in men

BACKGROUND

Glucagon-like Peptide-1 (GLP-1) is an incretin hormone secreted from the gastrointestinal tract that facilitates the glucose-dependent insulin response. Additionally, GLP-1 is thought to be involved in energy homeostasis. Currently little is known about GLP-1's responsiveness to an energy surplus, a fundamental cause of obesity and diabetes. Our objective was to examine the response of serum GLP-1 to short-term (7 day) overfeeding in young men.

METHODS

Seventy-two young men from the Canadian province of Newfoundland were recruited for the study. For 7-days, the subjects consumed 70% more calories than required at baseline.Various measurements including: anthropometrics, body composition, markers of glucose/lipid metabolism and serum total GLP-1, were taken at a fasted state before (day 1) and after (day 8) the challenge. Paired t-test analyses were used to assess the change in variables after the overfeeding period. Additionally, the relationship between serum GLP-1 and the measured variables at baseline and change due to overfeeding were analyzed.

RESULTS

Serum GLP-1 was significantly increased in all groups in response to the 7-day energy surplus, indicating the increase was independent of adiposity status. There was no significant difference in fasting GLP-1 at baseline between the normal weight and overweight/obese groups. At baseline, GLP-1 concentration negatively correlated with HDL-cholesterol and positively correlated with triacylglycerols and markers of insulin resistance in the overweight/obese group. Also GLP-1 was negatively correlated with change in percent gynoid fat in the overweight/obese subjects. Percent change in GLP-1 was negatively associated with percent change in gynoid fat in the normal weight group and positively associated with percent change in cholesterol in the overweight/obese group. Percentage change of circulating triacylglycerols was positively associated with percent change in GLP-1 in both adiposity groups.

CONCLUSION

Our findings showed that GLP-1 serum concentration is not a significant factor in determining obesity status. The increase of GLP-1 in all subjects regardless of obesity status, suggest GLP-1 serves as a protective role, counteracting energy surplus.

Saturated fat stimulates obesity and hepatic steatosis and affects gut microbiota composition by an enhanced overflow of dietary fat to the distal intestine

We studied the effect of dietary fat type, varying in polyunsaturated-to-saturated fatty acid ratios (P/S), on development of metabolic syndrome. C57Bl/6J mice were fed purified high-fat diets (45E% fat) containing palm oil (HF-PO; P/S 0.4), olive oil (HF-OO; P/S 1.1), or safflower oil (HF-SO; P/S 7.8) for 8 wk. A low-fat palm oil diet (LF-PO; 10E% fat) was used as a reference. Additionally, we analyzed diet-induced changes in gut microbiota composition and mucosal gene expression. The HF-PO diet induced a higher body weight gain and liver triglyceride content compared with the HF-OO, HF-SO, or LF-PO diet. In the intestine, the HF-PO diet reduced microbial diversity and increased the Firmicutes-to-Bacteroidetes ratio. Although this fits a typical obesity profile, our data clearly indicate that an overflow of the HF-PO diet to the distal intestine, rather than obesity itself, is the main trigger for these gut microbiota changes. A HF-PO diet-induced elevation of lipid metabolism-related genes in the distal small intestine confirmed the overflow of palm oil to the distal intestine. Some of these lipid metabolism-related genes were previously already associated with the metabolic syndrome. In conclusion, our data indicate that saturated fat (HF-PO) has a more stimulatory effect on weight gain and hepatic lipid accumulation than unsaturated fat (HF-OO and HF-SO). The overflow of fat to the distal intestine on the HF-PO diet induced changes in gut microbiota composition and mucosal gene expression. We speculate that both are directly or indirectly contributive to the saturated fat-induced development of obesity and hepatic steatosis.

Effect of Roux-en-Y gastric bypass vs sleeve gastrectomy on glucose and gut hormones: a prospective randomised trial

BACKGROUND

Laparoscopic Roux-en-Y gastric bypass (LRYGB) is the most common bariatric technique. Laparoscopic sleeve gastrectomy (LSG) is a restrictive procedure; the metabolic and endocrine effects of which remain unknown. We compared the effects of both procedures on glucose metabolism and fasting and meal-stimulated gut hormone levels.

METHODS

Seven patients were randomised to LRYGB and eight to LSG. All patients were evaluated before and at 3 and 12 months postoperatively. Plasma levels of glucose, insulin, ghrelin, leptin, peptide YY (PYY), GLP-1 and pancreatic polypeptide were measured before and after 10 and 60 min of a standard test meal ingestion.

RESULTS

Age, body mass index and preoperative hormone levels were similar in both groups. A significant reduction of plasma glucose and insulin levels was observed after surgery. Moreover, a normalisation of homeostatic model assessment for insulin resistance value was also seen after both procedures. The fasting and postprandial leptin levels were significantly lower in the LRYGB group. LSG was followed by a significant reduction in fasting ghrelin levels. In the LRYGB group, GLP-1 levels increased significantly after the test meal.

CONCLUSIONS

LRYGB and LSG markedly improved glucose homeostasis. Only LSG decreased fasting and postprandial ghrelin levels, whereas GLP-1 and PYY levels increased similarly after both procedures.

Circulating ghrelin and GLP-1 are not affected by habitual diet

BACKGROUND

Ghrelin and glucagon-like peptide-1 (GLP-1) are gut hormones known to induce hunger and satiety, respectively. Current knowledge about the effects of different macronutrients on circulating ghrelin and GLP-1 comes mainly from acute test meals, whereas little is known about the effects of chronic dietary intake on gut hormone secretion. This study was designed to examine whether 8-week habituation to diets with different percentages of carbohydrate and fat would affect serum ghrelin, GLP-1, and subjective hunger in a postabsorptive state and in response to a standard liquid mixed meal.

METHODS

Sixty-one overweight men and women were provided all food for 8 weeks of either a higher-carbohydrate/lower-fat diet (High-CHO/Low-FAT; 55% CHO, 18% PRO, 27% FAT) or a lower-carbohydrate/higher-fat diet (Low-CHO/High-FAT; 43% CHO, 18% PRO, 39% FAT). After overnight fasts at baseline and week 8, participants consumed a standard liquid meal (7 kcals/kg, 58.6% CHO, 17.4% PRO, 24% FAT). Blood was sampled before the meal and at 15, 60, 90, 120, 180, and 240 min to determine total serum ghrelin and active GLP-1. Hunger was assessed by a visual analog scale. Mixed models were used to evaluate whether the temporal patterns of total serum ghrelin and active GLP-1 differed with diet.

RESULTS

Although both diet groups reported greater hunger after 8 weeks (p=0.03), circulating ghrelin and GLP-1 were not affected by acclimation to different macronutrients.

CONCLUSION

Habituation to different diets does not appear to influence fasting ghrelin, fasting GLP-1, or responses of these gut hormones to a standard meal.

Physiology of weight loss surgery

The clinical outcomes achieved by bariatric surgery have been impressive. However, the physiologic mechanisms and complex metabolic effects of bariatric surgery are only now beginning to be understood. Ongoing research has contributed a large amount of data and shed new light on the science behind obesity and its treatment, and this article reviews the current understanding of metabolic and bariatric surgery physiology.

Gastric bypass surgery restores meal stimulation of the anorexigenic gut hormones glucagon-like peptide-1 and peptide YY independently of caloric restriction

BACKGROUND

The effects of gastric bypass surgery on the secretion of the anorexigenic gut-derived hormones glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), independent of caloric restriction and due to different dietary macronutrients, is not well characterized. This study examines the effects of a mixed-nutrient or high-fat liquid meal on the postprandial stimulation of GLP-1 and PYY following gastric bypass or equivalent hypocaloric diet.

METHODS

Total PYY and active GLP-1 were measured fasting and at multiple points after standardized mixed-nutrient and high-fat liquid meals in two matched groups of obese subjects. The meal stimulation tests were performed before and 14.6 ± 3.3 days after gastric bypass (GBP, n = 10) and before and after a 7-day hypocaloric liquid diet matching the post-GBP diet (control, n = 10).

RESULTS

Mixed-nutrient and high-fat postprandial GLP-1 levels increased following GBP (mixed-nutrient peak: 85.0 ± 28.6-323 ± 51 pg/ml, P < 0.01; high-fat peak: 81.8 ± 9.6-278 ± 49 pg/ml, P < 0.01), but not after diet (mixed-nutrient peak: 104.4 ± 9.4-114.9 ± 15.8 pg/ml, P = NS; high-fat peak: 118.1 ± 16.4-104.4 ± 10.8 pg/ml, P = NS). The postprandial PYY response also increased after GBP but not diet, though the increase in peak PYY did not reach statistical significance (GBP mixed-nutrient peak: 134.8 ± 26.0-220.7 ± 52.9 pg/ml, P = 0.09; GBP high-fat peak: 142.1 ± 34.6-197.9 ± 12.7 pg/ml, P = 0.07; diet mixed-nutrient peak: 99.8 ± 8.0-101.1 ± 13.3 pg/ml, P = NS; diet high-fat peak: 105.0 ± 8.8-103.1 ± 11.8 pg/ml, P = NS). The postprandial GLP-1 response was not affected by the macronutrient content of the meal. However, following GBP the mixed-nutrient PYY total area under the curve (AUC(0-120)) was significantly greater than the high-fat PYY AUC(0-120) (22,081 ± 5,662 pg/ml min vs. 18,711 ± 1,811 pg/ml min, P = 0.04).

CONCLUSIONS

Following GBP there is an increase in the postprandial stimulation of PYY and GLP-1 that is independent of caloric restriction. The phenomenon of "bariatric surgery-induced anorexia" may be linked to the increased levels after GBP.

Changes in gastrointestinal hormones and leptin after Roux-en-Y gastric bypass surgery

BACKGROUND

Roux-en-Y gastric bypass (RYGB) imparts long-term weight loss, the mechanisms for which are not well understood. Changes in leptin and gastrointestinal (GI) hormones, including glucagon-like peptide 1 (GLP-1), peptide YY (PYY), and ghrelin, may contribute to the relative success of RYGB compared with conventional weight loss methods. This study evaluated changes in GI hormones and leptin post-RYGB. The study also evaluated whether GI hormones differed after a short-term dose of protein or fat.

METHODS

GLP-1, PYY, ghrelin, and leptin were assessed in 16 women before RYGB and up to 1 year after RYGB. Plasma was collected before and at several times after a short-term equicaloric dose of protein or fat.

RESULTS

GLP-1 area under the curve (AUC) increased at week 6 and 1 year in the fat beverage (FAT-BEV) group compared with baseline. PYY AUC remained elevated at 1 year in the FAT-BEV group. Ghrelin AUC decreased at week 2, week 6, and 1 year in the protein beverage (PRO-BEV) group compared with baseline. Ghrelin AUC was lower in the PRO-BEV group compared with the FAT-BEV group at week 6. Fasted leptin decreased at all visits in both groups and was lower in the FAT-BEV group compared with the PRO-BEV group at 1 year.

CONCLUSIONS

Changes from baseline were evident for all GI hormones and leptin; some differences were evident soon after surgery (ghrelin, leptin), whereas others were maintained long term (GLP-1, PYY, ghrelin, leptin). In response to a short-term stimulus, protein suppressed ghrelin and fat potently stimulated GLP-1 and PYY. Future work in this area is warranted.

Mass spectrometry-based neuropeptidomics of secretory vesicles from human adrenal medullary pheochromocytoma reveals novel peptide products of prohormone processing

Neuropeptides are required for cell-cell communication in the regulation of physiological and pathological processes. While selected neuropeptides of known biological activities have been studied, global analyses of the endogenous profile of human peptide products derived from prohormones by proteolytic processing in vivo are largely unknown. Therefore, this study utilized the global, unbiased approach of mass spectrometry-based neuropeptidomics to define peptide profiles in secretory vesicles, isolated from human adrenal medullary pheochromocytoma of the sympathetic nervous system. The low molecular weight pool of secretory vesicle peptides was subjected to nano-LC-MS/MS with ion trap and QTOF mass spectrometry analyzed by different database search tools (InsPecT and Spectrum Mill). Peptides were generated by processing of prohormones at dibasic cleavage sites as well as at nonbasic residues. Significantly, peptide profiling provided novel insight into newly identified peptide products derived from proenkephalin, pro-NPY, proSAAS, CgA, CgB, and SCG2 prohormones. Previously unidentified intervening peptide domains of prohormones were observed, thus providing new knowledge of human neuropeptidomes generated from precursors. The global peptidomic approach of this study demonstrates the complexity of diverse neuropeptides present in human secretory vesicles for cell-cell communication.

Changes in gastrointestinal hormones and leptin after Roux-en-Y gastric bypass procedure: a review

Roux-en-Y gastric bypass is a well-accepted tool for the treatment of obesity and, compared to conventional weight loss methods (eg, diet and exercise) and other weight loss surgeries (eg, gastric banding), it results in considerable weight loss that is maintained long term. Although successful, the mechanisms for weight loss are not completely understood and it is thought that gastrointestinal hormones play a role. Several gastrointestinal hormones have been identified for their effects on appetite, including glucagon-like peptide-1 (GLP-1), peptide tyrosine-tyrosine (PYY), leptin, and ghrelin. This review encompasses a literature search that included 45 primary articles and shows that there are alterations in GLP-1, PYY, leptin, and ghrelin postoperatively. GLP-1 and PYY concentrations were usually found to be higher, whereas ghrelin levels were typically lower post- Roux-en-Y gastric bypass than in individuals with obesity, those who were overweight or of normal weight, and in those who underwent procedures other than Roux-en-Y gastric bypass or who achieved weight loss by lifestyle modification. An understanding of how gastrointestinal hormones change after Roux-en-Y gastric bypass may help dietetics practitioners optimize nutrition care for this patient population. A review of the literature also highlighted some research gaps that should be taken into consideration when designing future studies.