Effects of Fat and Protein Preloads on Pouch Emptying, Intestinal Transit, Glycaemia, Gut Hormones, Glucose Absorption, Blood Pressure and Gastrointestinal Symptoms After Roux-en-Y Gastric Bypass

Physiology and Pharmacology of Effects of GLP-1-based Therapies on Gastric, Biliary and Intestinal Motility

Glucagon-like peptide-1 (GLP-1) receptor agonists and the dual GLP-1- and glucose-dependent insulinotropic polypeptide receptor co-agonist tirzepatide (referred to here collectively as "GLP-1-based therapy") are incretin-based therapies being used increasingly in the management of both type 2 diabetes and obesity. They are now recognized to have beneficial effects beyond improved glycemic control and weight loss, including cardiovascular and renal protection. GLP-1-based therapy also slows gastric emptying, which has benefits (lowering postprandial glucose), but also potential risks (eg, hypoglycemia in individuals on insulin or sulphonylurea therapy). Their effects on the gallbladder may also be beneficial, contributing to reducing postprandial triglycerides, but they also potentially increase the risk of biliary disease. In this review, we summarize the effects of GLP-1 and incretin-based therapeutics on gastric, biliary and small intestinal function. An improved understanding of these effects will optimize the use of these drugs.

Whey Protein Premeal Lowers Postprandial Glucose Concentrations in Adults Compared with Water-The Effect of Timing, Dose, and Metabolic Status: a Systematic Review and Meta-analysis

BACKGROUND

Serving whey protein before a meal in order to lower postprandial blood glucose concentrations is known as a premeal. The underlying mechanisms are only partly understood but may involve stimulation of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and insulin secretion together with a slower gastric emptying rate.

OBJECTIVES

The objective of this systematic review and meta-analysis was to review all randomized clinical trials investigating premeals with whey protein in comparison with a nonactive comparator (control) that evaluated plasma glucose, GLP-1, GIP, insulin, and/or gastric emptying rate. Secondary aims included subgroup analyses on the timing and dose of the premeal together with the metabolic state of the participants [lean, obese, and type 2 diabetes mellitus (T2DM)].

METHODS

We searched EMBASE, CENTRAL, PUBMED, and clinicaltrials.gov and found 16 randomized crossover trials with a total of 244 individuals. The last search was performed on 9 August, 2022.

RESULTS

Whey protein premeals lowered peak glucose concentration by -1.4 mmol/L [-1.9 mmol/L; -0.9 mmol/L], and the area under the curve for glucose was -0.9 standard deviation (SD) [-1.2 SD; -0.6 SD] compared with controls (high certainty). In association with these findings, whey protein premeals elevated GLP-1 (low certainty) and peak insulin (high certainty) concentrations and slowed gastric emptying rate (high certainty) compared with controls. Subgroup analyses showed a more pronounced and prolonged glucose-lowering effect in individuals with T2DM compared with participants without T2DM. The available evidence did not elucidate the role of GIP. The protein dose used varied between 4 and 55 g, and meta-regression analysis showed that the protein dose correlated with the glucose-lowering effects.

CONCLUSIONS

In conclusion, whey protein premeals lower postprandial blood glucose, reduce gastric emptying rate, and increase peak insulin. In addition, whey protein premeals may elevate plasma concentrations of GLP-1. Whey protein premeals may possess clinical potential, but the long-term effects await future clinical trials.

Do Body Composition and Values of Selected Nutritional Status Indices Influence the Glycaemic Index Values of Vegetarian Dishes? A Pilot Study in a Group of Older Women

An ageing population brings with it the need for public policy to respond to the demands and health needs of this group of people. The ageing process has been shown to be associated with changes in body composition. These mainly concern a decrease in muscle mass and an increase in body fat. Body composition and other indicators of nutritional status are important factors differentiating carbohydrate management. Glycaemic index (GI) values may be affected by differences resulting from individual metabolism. The rate of carbohydrate digestion is also influenced by a number of factors, including the degree to which the product is processed, the structure of the starch, and the presence of protein, fat and dietary fibre. Available studies do not provide information on the glycaemic response following the consumption of specific products by older people with varying BMI and body composition. Therefore, the aim of this study was to evaluate the effect of the body mass index (BMI) values of women aged 50-80 years on the glycaemic response after eating vegetarian meals and the influence of selected indices of nutritional status on their GI values. It has been shown that the areas under the glycaemic curves after the consumption of the tested foods, both traditional and modified, are higher in the group of overweight and obese women. Nevertheless, the GI of meals consumed by those with a BMI ≥ 25.0 kg/m² is lower than that of foods consumed by women with normal values of this index. In the group of women with BMI 18.5-24.9 kg/m², on the basis of an analysis of the obtained correlations, it was observed that the GI value of modified products depends on the percentage of body fat (FM%) (p = 0.0363) and the percentage of fat free mass (FFM%) (p = 0.0363), and, in the case of traditional products, also on the percentage of total body water (%) (p = 0.0133). In the group of women with a BMI ≥ 25.0 kg/m², significant correlations were only found between the GI of modified foods and the waist-to-hip ratio (WHR) (p = 0.0363) and the ratio of waist circumference to height (WHtR) (p = 0.0369) indices. The GI values of food set solely with the participation of young, healthy people should not be the basis for the nutrition planning of all groups of people.

A systematic review of whey protein supplementation effects on human glycemic control: A mechanistic insight

BACKGROUND/AIMS

Some studies showed that dietary factors such as whey protein (WP) are effective on glycemic regulation. Due to the current controversy about WP effects and mechanisms of its action on glycemic control, we conducted this systematic review to shed light on the subject.

METHODS

Web of Science, Medline (Pubmed), and Scopus online databases were searched from 2012 up to February 2022 using the following keywords: "whey protein" and "glycemic control"/"glycemia"/"glucose"/"insulin". The search included original English articles, human clinical trials with WP supplementation and measurement of glucose or insulin as an outcome, studies on healthy individuals/patients with diabetes mellitus (DM)/impaired fasting glucose (IFG).

RESULTS

Title/abstract of 1991 studies were reviewed. After excluding studies due to inappropriate full title and duplication, and exercising inclusion criteria, 58 studies were reviewed in detail. Ample evidence showed that WP decreased postprandial glucose incremental area under the curve (iAUC) and increased iAUCs of insulin and incretin hormones. WP affects glycemic control mainly through stimulating insulin and incretins secretion, slowing gastric emptying, and appetite suppression.

CONCLUSION

Although most of the recent evidence showed beneficial effects of WP supplementation on glycemic response, further long-term clinical trials are required which assess the long-term impact of WP supplementation and its exact mechanisms.

Exaggerated postprandial GLP-1 secretion following esophagectomy is not associated with gastric emptying and intestinal transit

Esophagectomy causes postprandial symptoms associated with an exaggerated postprandial gut hormone response. This study aimed to compare the gastrointestinal transit time of patients 1 year after esophagectomy with unoperated controls, including its relation to satiety gut hormone release. In this cross-sectional study, consecutive, disease-free patients after esophagectomy with pyloroplasty were compared with unoperated control subjects to assess gastric emptying (GE) and cecal arrival time (CAT). Serial plasma samples were collected before, and for 300 minutes after, a mixed-meal challenge. Body composition was assessed, and symptom scores were calculated. Eleven patients 1 year post-esophagectomy (age: 62.6 ± 9.8, male: 82%) did not show a significantly different GE pattern compared with 10 control subjects (P = 0.245). Rather, patients could be categorized bimodally as exhibiting either rapid or slow GE relative to controls. Those with rapid GE trended toward a higher postprandial symptom burden (P = 0.084) without higher postprandial glucagon-like peptide-1 (GLP-1) secretion (P = 0.931). CAT was significantly shorter after esophagectomy (P = 0.043) but was not significantly associated with GE, GLP-1 secretion, or symptom burden. Neither early nutrient delivery to the proximal small intestine nor to the colon explains the exaggerated postprandial GLP-1 response after esophagectomy. GE varies significantly in these patients despite consistent pyloric management.

Gastrointestinal pH, Motility Patterns, and Transit Times After Roux-en-Y Gastric Bypass

BACKGROUND

Studies investigating the underlying pathophysiology are needed to help explain and understand the postoperative complications following Roux-en-Y gastric bypass (RYGB) surgery. This study aimed to characterize segmental gastrointestinal pH profiles, motility measures, and transit times in patients with RYGB.

MATERIALS AND METHODS

Nineteen patients with RYGB underwent a standardized wireless motility capsule assessment. The oro-cecal segment was defined from capsule ingestion until the passage of the ileocecal junction. Segmental median pH, motility index, and transit time were determined for the oro-cecal and colonic segment as well as for the first and last hour of both these segments. For comparison to reference values, data from 17 healthy age- and gender-matched controls was used. A mixed effect model was used to describe differences between groups.

RESULTS

Median pH was high in patients with RYGB during the first hour of the oro-cecal segment (6.45 ± 0.4 vs 3.65 ± 1.55 pH units for healthy controls; P < 0.001), as well as during the entire oro-cecal segment (6.97 ± 0.4 vs 5.51 ± 1.1 pH units; P < 0.001). The same was evident for the median motility index (152 ± 64 vs 35.8 ± 31.1 mmHg*sec/min; P < 0.001 and 130 ± 65.9 vs 89.1 ± 20 mmHg*sec/min; P < 0.012, respectively). Median motility index was low the first hour of the colon (55.2 ± 45.7 vs 122 ± 77.9 mmHg*sec/min; P < 0.002). Additionally, patients had short oro-cecal transit time (5.8 ± 1.6 vs 7.6 ± 1.4 h; P < 0.001) and long colonic transit time (29.4 ± 17.5 vs 19.6 ± 12.2 h; P = 0.048).

CONCLUSIONS

In patients with RYGB, the oro-cecal segment was characterized by an alkaline intraluminal environment, high motility activity, and short transit time. In contrast, colonic transit time was long.

Adaptations in gastrointestinal physiology after sleeve gastrectomy and Roux-en-Y gastric bypass

Linked to the growing obesity epidemic, demand for bariatric and metabolic surgery has increased, the most common procedures being sleeve gastrectomy and Roux-en-Y gastric bypass. Originally, bariatric procedures were described as purely restrictive, malabsorptive, or combined restrictive-malabsorptive procedures limiting food intake, nutrient absorption, or both. Nowadays, anatomical alterations are known to affect gastrointestinal physiology, which in turn affects the digestion and absorption of nutrients and drugs. Therefore, understanding gastrointestinal physiology is crucial to prevent postoperative nutritional deficiencies and to optimise postoperative drug therapy. Preclinical and clinical research indicates that sleeve gastrectomy accelerates liquid and solid gastric emptying and small intestinal transit, and increases bile acid serum levels, whereas its effects on gastrointestinal acidity, gastric and pancreatic secretions, surface area, and colonic transit remain largely unknown. Roux-en-Y gastric bypass diminishes gastric acid secretion, accelerates liquid gastric emptying, and increases bile acid serum levels, but its effects on intestinal pH, solid gastric emptying, intestinal transit time, gastric enzyme secretions, and surface area remain largely unknown. In this Review, we summarise current knowledge of the effects of these two procedures on gastrointestinal physiology and assess the knowledge gaps.

The Phantom Satiation Hypothesis of Bariatric Surgery

The excitation of vagal mechanoreceptors located in the stomach wall directly contributes to satiation. Thus, a loss of gastric innervation would normally be expected to result in abrogated satiation, hyperphagia, and unwanted weight gain. While Roux-en-Y-gastric bypass (RYGB) inevitably results in gastric denervation, paradoxically, bypassed subjects continue to experience satiation. Inspired by the literature in neurology on phantom limbs, I propose a new hypothesis in which damage to the stomach innervation during RYGB, including its vagal supply, leads to large-scale maladaptive changes in viscerosensory nerves and connected brain circuits. As a result, satiation may continue to arise, sometimes at exaggerated levels, even in subjects with a denervated or truncated stomach. The same maladaptive changes may also contribute to dysautonomia, unexplained pain, and new emotional responses to eating. I further revisit the metabolic benefits of bariatric surgery, with an emphasis on RYGB, in the light of this phantom satiation hypothesis.

Insights from the Impact of Meal Composition on Glucose Profile Towards Post-bariatric Hypoglycemia Management

BACKGROUND/AIM

The need to improve post-bariatric hypoglycemia (PBH) diagnosis and clinical management is well recognized. Our aim was to evaluate the influence of meal nutritional composition on interstitial fluid glucose (IFG) profiles and symptom profile after Roux-en-Y gastric bypass (RYGB).

METHODS

Seventeen subjects previously submitted to RYGB were allocated into two groups of symptomatic (n = 9) or control individuals (n = 8), according to spontaneous report of symptoms suggestive of hypoglycemia. Subjects were provided with a food and symptom diary (FSD) to record dietary intake and symptoms experienced, while using a flash glucose monitoring (FGM) system for 14 days.

RESULTS

Postprandial symptom reports occurred in 70.5% of subjects (88.9% vs 50.0%, p = 0.0790, symptomatic vs control), although symptoms with concurrent IFG < 54 mg/dL and within 54 to 69 mg/dL were only observed in 31.9% and 4.8% of the events in the symptomatic vs control group, respectively (p = 0.0110). Daily glucose profiles, total energy, and macronutrients intake were not significantly different between the groups. However, nutritional composition of meals preceding reported symptoms had lower protein (3.2 g ± 1.0 g vs 7.7 g ± 0.5 g, p = 0.0286) or higher sugar (11.6 g ± 2.4 g vs 4.3 g ± 0.9 g, p = 0.0333) content.

CONCLUSIONS

Postprandial symptoms are often in patients after RYGB. Concurrent hypoglycemia only occurs in up to a third of the symptomatic episodes being more frequent in patients that spontaneously reported complaints. Hypoglycemia is more likely to be triggered by meals with a low protein or high sugar content. These findings highlight the putative role of meal composition in eliciting PBH and reinforce the need to refine nutritional intervention.

Development of a delayed-release nutrient for appetite control in adults with obesity and type 2 diabetes and initial clinical testing in a single dose randomized controlled trial

Background and objectives

Delivery of nutrients directly to the small intestine, either via enteral feeding tube or by gastric bypass surgery, is associated with increased levels of appetite-suppressing and glucoregulatory hormones, including GLP-1, and reduced appetite. Achieving these changes non-invasively using formulated foods may be of therapeutic benefit in individuals with obesity and related comorbidities. The aim of this pilot study was to determine the effect of a single dose of a novel delayed-release nutrient (DRN) on glucose, GLP-1, c-peptide, insulin, and appetite in adults with obesity and type 2 diabetes.

Subjects and methods

We formulated an all-natural, generally recognized as safe (‘GRAS”) DRN and conducted a randomized prospective crossover trial. Nineteen adults with obesity and type 2 diabetes underwent paired 3-h meal tolerance tests (MTT) in randomized order 1–4 weeks apart. Subjects ingested a single dose of DRN and the same nutrients as unformulated powders (UN).

Results

For DRN compared with UN, the maximal concentration (Cmax) was significantly lower for glucose, c-peptide, and insulin, and the time of maximal concentration (Tmax) was significantly delayed. While Tmax for GLP-1 was also significantly delayed following DRN compared with UN (45 min later; p = 0.26), Cmax did not differ significantly. GLP-1 rose significantly during the last 90 min of the 3-h MTT (β₁ = 0.16 pg/mL/min, p = 0.025), while following UN it decreased (β₁ = −0.21 pg/mL/min, p = 0.0026) (p difference = 0.0003). There were minimal differences in seven measures of appetite and adverse symptoms between DRN and UN.

Conclusions

We conclude that nutrient can be formulated using all-natural ingredients to induce a delayed rise in GLP-1. Further testing is needed to determine the amount and site of nutrient release, when maximum GLP-1 levels occur, and if modification of the formulation specifications and dose are associated with appetite and glucose control.

Impact of gastric emptying and small intestinal transit on blood glucose, intestinal hormones, glucose absorption in the morbidly obese

This study evaluated gastric emptying (GE) and small intestinal (SI) transit in people with morbid obesity and their relationships to glycaemia, incretin hormones, and glucose absorption METHODS: GE and caecal arrival time (CAT) of a mixed meal were assessed in 22 morbidly obese (50.2 ± 2.5 years; 13 F:9 M; BMI: 48.6 ± 1.8 kg/m2) and 10 lean (38.6 ± 8.4 years; 5 F:5 M; BMI: 23.9 ± 0.7 kg/m2) subjects, using scintigraphy. Blood glucose, plasma 3-O-methylglucose, insulin, glucagon, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) were measured. Insulin sensitivity and resistance were also quantified RESULTS: When compared with lean subjects, GE (t50: 60.7 ± 6.5 vs. 41.1 ± 7.3 min; P  = 0.04) and CAT (221.5 ± 9.8 vs. 148.0 ± 7.1 min; P =  0.001) of solids were prolonged in morbid obesity. Postprandial rises in GIP (P = 0.001), insulin (P  = 0.02), glucose (P = 0.03) and 3-O-methylglucose (P = 0.001) were less. Whereas GLP-1 increased at 45 mins post-prandially in lean subjects, there was no increase in the obese (P  = 0.04). Both fasting (P = 0.045) and postprandial (P = 0.012) plasma glucagon concentrations were higher in the obese CONCLUSIONS: GE and SI transit are slower in the morbidly obese, and associated with reductions in postprandial glucose absorption, and glycaemic excursions, as well as plasma GIP and GLP-1.

Medical nutrition therapy for post-bariatric hypoglycemia: practical insights

Hypoglycemia is increasingly recognized as a complication of bariatric surgery. Although medications are often required, medical nutrition therapy remains the key cornerstone for successful prevention of hypoglycemia in patients with post-bariatric hypoglycemia (PBH). We provide suggested approaches to the dietary management of PBH, incorporating data from both the medical literature and extensive clinical experience in an academic referral center for PBH. The overall goal of medical nutrition therapy for PBH is to reduce postprandial surges in glucose, which often trigger surges in insulin secretion and promote subsequent hypoglycemia. Thus, strategies focus on controlled portions of low glycemic index carbohydrates, avoidance of rapidly-absorbed carbohydrates, adjustment of timing of meals and snacks, and attention to personal and cultural barriers to implementation.

Ghrelin, CCK, GLP-1, and PYY(3-36): Secretory Controls and Physiological Roles in Eating and Glycemia in Health, Obesity, and After RYGB

The efficacy of Roux-en-Y gastric-bypass (RYGB) and other bariatric surgeries in the management of obesity and type 2 diabetes mellitus and novel developments in gastrointestinal (GI) endocrinology have renewed interest in the roles of GI hormones in the control of eating, meal-related glycemia, and obesity. Here we review the nutrient-sensing mechanisms that control the secretion of four of these hormones, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine tyrosine [PYY(3-36)], and their contributions to the controls of GI motor function, food intake, and meal-related increases in glycemia in healthy-weight and obese persons, as well as in RYGB patients. Their physiological roles as classical endocrine and as locally acting signals are discussed. Gastric emptying, the detection of specific digestive products by small intestinal enteroendocrine cells, and synergistic interactions among different GI loci all contribute to the secretion of ghrelin, CCK, GLP-1, and PYY(3-36). While CCK has been fully established as an endogenous endocrine control of eating in healthy-weight persons, the roles of all four hormones in eating in obese persons and following RYGB are uncertain. Similarly, only GLP-1 clearly contributes to the endocrine control of meal-related glycemia. It is likely that local signaling is involved in these hormones' actions, but methods to determine the physiological status of local signaling effects are lacking. Further research and fresh approaches are required to better understand ghrelin, CCK, GLP-1, and PYY(3-36) physiology; their roles in obesity and bariatric surgery; and their therapeutic potentials.

Influence of dietary protein and its amino acid composition on postoperative outcomes after gastric bypass surgery: a systematic review

CONTEXT

Bariatric surgery is an effective method to reduce morbid obesity. Nutritional counseling is essential to achieve maximal treatment success and to avoid long-term complications. Increased dietary protein intake may improve various postoperative results.

OBJECTIVE

The aim of this systematic review is to examine the relationship between intake of dietary protein or supplementation with amino acids and postoperative outcomes after gastric bypass surgery.

DATA SOURCES

A systematic literature search was conducted in 4 electronic databases: Cochrane, Embase, PubMed, and Scopus.

STUDY SELECTION

The initial search retrieved 7333 hits, which included 2390 duplicates.

DATA EXTRACTION

Tweny-three studies with varying study designs, interventions, and outcomes were included.

RESULTS

Studies did not provide convincing evidence of a beneficial effect on any postoperative outcome.

CONCLUSIONS

The study of the influence of protein and its amino acid composition represents an important developing domain of knowledge and warrants further attention considering the popularity of bariatric surgery. Future studies should include a clear description of the quantity and composition of proteins and amino acids in the diet or supplement.

Mechanisms Regulating Insulin Response to Intragastric Glucose in Lean and Non-Diabetic Obese Subjects: A Randomized, Double-Blind, Parallel-Group Trial

Background/Objectives

The changes in blood glucose concentrations that result from an oral glucose challenge are dependent on the rate of gastric emptying, the rate of glucose absorption and the rate of insulin-driven metabolism that include the incretins, glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 (GLP-1). The rate of insulin-driven metabolism is clearly altered in obese subjects, but it is controversial which of these factors is predominant. We aimed to quantify gastric emptying, plasma insulin, C-peptide, glucagon and glucose responses, as well as incretin hormone secretions in obese subjects and healthy controls during increasing glucose loads.

Subjects/Methods

The study was conducted as a randomized, double-blind, parallel-group trial in a hospital research unit. A total of 12 normal weight (6 men and 6 women) and 12 non-diabetic obese (BMI > 30, 6 men and 6 women) participants took part in the study. Subjects received intragastric loads of 10 g, 25 g and 75 g glucose dissolved in 300 ml tap water.

Results

Main outcome measures were plasma GLP-1 and GIP, plasma glucagon, glucose, insulin, C-peptide and gastric emptying. The primary findings are: i) insulin resistance (P < 0.001) and hyperinsulinemia (P < 0.001); ii) decreased insulin disposal (P < 0.001); iii) trend for reduced GLP-1 responses at 75 g glucose; and iv) increased fasting glucagon levels (P < 0.001) in obese subjects.

Conclusions

It seems that, rather than changes in incretin secretion, fasting hyperglucagonemia and consequent hyperglycemia play a role in reduced disposal of insulin, contributing to hyperinsulinemia and insulin resistance.

Trial Registration

ClinicalTrials.gov NCT01875575