An investigation of the neural mechanisms underlying the efficacy of the adjustable gastric band

Mechanisms of Action of Bariatric Surgery on Body Weight Regulation

Bariatric surgery is an effective treatment modality for obesity and obesity-associated complications. Weight loss after bariatric surgery was initially attributed to anatomic restriction or reduced energy absorption, but now it is understood that surgery treats obesity by influencing the subcortical areas of the brain to lower adipose tissue mass. There are three major phases of this process: initially the weight loss phase, followed by a phase where weight loss is maintained, and in a subset of patients a phase where weight is regained. These phases are characterized by altered appetitive behavior together with changes in energy expenditure. The mechanisms associated with the rearrangement of the gastrointestinal tract include central appetite control, release of gut peptides, change in microbiota and bile acids. However, the exact combination and timing of signals remain largely unknown.

Gut microbiome: Linking together obesity, bariatric surgery and associated clinical outcomes under a single focus

Obesity is increasingly prevalent in the post-industrial era, with increased mortality rates. The gut microbiota has a central role in immunological, nutritional and metabolism mediated functions, and due to its multiplexity, it is considered an independent organ. Modern high-throughput sequencing techniques have allowed phylogenetic exploration and quantitative analyses of gut microbiome and improved our current understanding of the gut microbiota in health and disease. Its role in obesity and its changes following bariatric surgery have been highlighted in several studies. According to current literature, obesity is linked to a particular microbiota profile that grants the host an augmented potential for calorie release, while limited diversity of gut microbiome has also been observed. Moreover, bariatric surgery procedures represent effective interventions for sustained weight loss and restore a healthier microbiota, contributing to the observed fat mass reduction and lean mass increase. However, newer evidence has shown that gut microbiota is only partially recovered following bariatric surgery. Moreover, several targets including FGF15/19 (a gut-derived peptide), could be responsible for the favorable metabolic changes of bariatric surgery. More randomized controlled trials and larger prospective studies that include well-defined cohorts are required to better identify associations between gut microbiota, obesity, and bariatric surgery.

Mechanisms of Weight Loss After Obesity Surgery

Obesity surgery remains the most effective treatment for obesity and its complications. Weight loss was initially attributed to decreased energy absorption from the gut but has since been linked to reduced appetitive behavior and potentially increased energy expenditure. Implicated mechanisms associating rearrangement of the gastrointestinal tract with these metabolic outcomes include central appetite control, release of gut peptides, change in microbiota, and bile acids. However, the exact combination and timing of signals remain largely unknown. In this review, we survey recent research investigating these mechanisms, and seek to provide insights on unanswered questions over how weight loss is achieved following bariatric surgery which may eventually lead to safer, nonsurgical weight-loss interventions or combinations of medications with surgery.

Pre-operative Restraint and Post-operative Hunger, Disinhibition and Emotional Eating Predict Weight Loss at 2 Years Post-laparoscopic Adjustable Gastric Banding

INTRODUCTION

A principal mechanism of action in bariatric surgery is reduction in calorie consumption due to decreased hunger and increased satiety. Patients' ability to perceive post-operative changes to their hunger is therefore central to optimal results. This study examined factors that may impact how patients perceive post-operative hunger and how perception of hunger impacts eating and subsequent weight loss after laparoscopic adjustable gastric banding (LAGB).

METHODS

Patients undertaking LAGB (n = 147) provided pre-surgery and 2-year weight loss data and pre-surgery and 12-month psychological data (perception of hunger, disinhibition related to eating, emotional eating).

RESULTS

Path analysis demonstrated that patients with lower levels of pre-surgery cognitive restraint over eating experienced significantly greater reduction in perception of hunger at 12 months post-surgery. Perceived reduction in hunger was significantly associated with lower levels of both emotional eating and disinhibited eating. Finally, reduced emotional eating at 12 months significantly predicted 9% of the variance in percentage of total weight loss (%TWL) at 2 years after surgery.

CONCLUSION

These initial findings suggest that preparation for bariatric surgery may be enhanced by psychoeducation regarding cognitive restraint over eating and its effect on hunger perception. In addition, psychological treatment that focuses on identifying and responding to changes in hunger may contribute to improved outcomes for those who have difficulty adjusting to post-operative eating behaviours.

Mechanisms of Weight Loss After Sleeve Gastrectomy and Adjustable Gastric Banding: Far More Than Just Restriction

Obesity has reached global epidemic proportions in recent decades. Bariatric surgery is currently accepted as most effective in alleviating morbid obesity and related disorders. Sleeve gastrectomy (SG) and adjustable gastric banding (AGB) have gained popularity since the beginning of this century because of their efficacy, safety, and simplicity. SG, in particular, has emerged as the most popular bariatric procedure because of its simpler concept and shorter operative time compared with gastric bypass. Caloric restriction, however, cannot account for the sustained weight loss and improved glucose metabolism seen following SG and AGB. Other mechanisms, including changes in gastrointestinal hormone secretion, rearrangement of hypothalamic and vagal control, alteration in energy expenditure, and re-regulation of bile acid metabolism and the intestinal flora environment, are thought to contribute to the postoperative benefits. This review focuses on clinical and experimental literature addressing the potential mechanisms for SG and AGB procedures in human and animal models. Understanding such mechanisms can provide important insight into how current gastric restrictive procedures work and how future treatments of obesity, both surgical and nonsurgical, can be developed.

Upper Gastrointestinal Function in Morbidly Obese Adolescents Before and 6 Months After Gastric Banding

BACKGROUND

The effects of laparoscopic adjustable gastric band (LAGB) placement on upper gastrointestinal tract function in obese adolescents are unknown. Therefore, our aim was to determine the short-term effects of LAGB on esophageal motility, gastroesophageal reflux, gastric emptying, appetite-regulatory hormones, and perceptions of post-prandial hunger and fullness.

METHODS

This study was part of a prospective cohort study (March 2009-December 2015) in one tertiary referral hospital. The study included obese adolescents (14-18 years) with a body mass index (BMI) > 40 (or ≥ 35 with comorbidities). Gastric emptying was assessed by ¹³C-octanoic acid breath test, pharyngeal, and esophageal motor function by high-resolution manometry with impedance (HRIM), and appetite and other perceptions using 100-mm visual analogue scales. Dysphagia symptoms were scored using a Dakkak questionnaire. Data were compared pre- and post-LAGB placement and at a 6-month follow-up.

RESULTS

Based upon analysis of 15 adolescents, at the 6-month follow-up, LAGB placement: (i) led to a significant reduction in weight and BMI; (ii) increased fullness and decreased hunger post-meal; (iii) increased symptoms of dysphagia after solid food; and, despite these effects, (iv) caused little or no changes to appetite hormones, while (v) effects on gastric emptying, esophageal motility, esophageal bolus transport, and esophageal emptying were not significant.

CONCLUSION

In adolescents, LAGB improved BMI and altered the sensitivity to nutrients without significant effects on upper gastrointestinal tract physiology at the 6-month follow-up.

Meal patterns after bariatric surgery in mice and rats

With behavioral and pharmacological interventions continuously failing to tackle the obesity epidemic, bariatric surgery has been hailed as the most effective treatment strategy. Current literature suggests that bariatric surgery successfully decreases body weight and excess fat mass through targeting both variables of the energy homeostasis - energy intake and energy expenditure. Here we review current knowledge on changes in caloric consumption, an important arm in the energy balance equation, in rodent models of bariatric surgery. In particular, circadian feeding dynamics, post-surgical caloric intake at both "rapid weight loss" phase and "weight maintenance" phase, as well as meal pattern analysis will be the subject of this review. Considering that different types of bariatric surgery may trigger differential energy intake dynamics resulting in variable weight loss outcomes, the effects of most popular surgeries - vertical sleeve gastrectomy (VSG), Roux-en-Y gastric bypass (RYGB), and gastric banding (GB) - are elaborated. Potential candidate mechanisms underlying alterations in food intake and meal patterns following different bariatric procedures are briefly discussed at the end.

Metabolic and Endocrine Consequences of Bariatric Surgery

Obesity is one of the most serious worldwide epidemics of the twenty-first century according to the World Health Organization. Frequently associated with a number of comorbidities, obesity threatens and compromises individual health and quality of life. Bariatric surgery (BS) has been demonstrated to be an effective treatment to achieve not only sustained weight loss but also significant metabolic improvement that goes beyond mere weight loss. The beneficial effects of BS on metabolic traits are so widely recognized that some authors have proposed BS as metabolic surgery that could be prescribed even for moderate obesity. However, most of the BS procedures imply malabsorption and/or gastric acid reduction which lead to nutrient deficiency and, consequently, further complications could be developed in the long term. In fact, BS not only affects metabolic homeostasis but also has pronounced effects on endocrine systems other than those exclusively involved in metabolic function. The somatotropic, corticotropic, and gonadal axes as well as bone health have also been shown to be affected by the various BS procedures. Accordingly, further consequences and complications of BS in the long term in systems other than metabolic system need to be addressed in large cohorts, taking into account each bariatric procedure before making generalized recommendations for BS. In this review, current data regarding these issues are summarized, paying special attention to the somatotropic, corticotropic, gonadal axes, and bone post-operative health.

Food Intake and Eating Behavior After Bariatric Surgery

Obesity is an escalating global chronic disease. Bariatric surgery is a very efficacious treatment for obesity and its comorbidities. Alterations to gastrointestinal anatomy during bariatric surgery result in neurological and physiological changes affecting hypothalamic signaling, gut hormones, bile acids, and gut microbiota, which coalesce to exert a profound influence on eating behavior. A thorough understanding of the mechanisms underlying eating behavior is essential in the management of patients after bariatric surgery. Studies investigating candidate mechanisms have expanded dramatically in the last decade. Herein we review the proposed mechanisms governing changes in eating behavior, food intake, and body weight after bariatric surgery. Additive or synergistic effects of both conditioned and unconditioned factors likely account for the complete picture of changes in eating behavior. Considered application of strategies designed to support the underlying principles governing changes in eating behavior holds promise as a means of optimizing responses to surgery and long-term outcomes.

Central Modulation of Energy Homeostasis and Cognitive Performance After Bariatric Surgery

In moderately or morbidly obese patients, bariatric surgery has been proven to be an effective therapeutic approach to control body weight and comorbidities. Surgery-mediated modulation of brain function via modified postoperative secretion of gut peptides and vagal nerve stimulation was identified as an underlying mechanism in weight loss and improvement of weight-related diseases. Increased basal and postprandial plasma levels of gastrointestinal hormones like glucagon-like peptide 1 and peptide YY that act on specific areas of the hypothalamus to reduce food intake, either directly or mediated by the vagus nerve, are observed after surgery while suppression of meal-induced ghrelin release is increased. Hormones released from the adipose tissue like leptin and adiponectin are also affected and leptin plasma levels are reduced in treated patients. Besides homeostatic control of body weight, surgery also changes hedonistic behavior in regard to food intake and cognitive performance involving the limbic system and prefrontal areas.

Medical devices for the treatment of obesity

Obesity is a major public health concern that leads to numerous metabolic, mechanical and psychological complications. Although lifestyle interventions are the cornerstone of obesity management, subsequent physiological neurohormonal adaptations limit weight loss, strongly favour weight regain and counteract sustained weight loss. A range of effective therapies are therefore needed to manage this chronic relapsing disease. Bariatric surgery delivers substantial, durable weight loss but limited access to care, perceived high risks and costs restrict uptake. Medical devices are uniquely positioned to bridge the gap between more conservative lifestyle intervention and weight-loss pharmacotherapy and more disruptive bariatric surgery. In this Review, we examine the range of gastrointestinal medical devices that are available in clinical practice to treat obesity, as well as those that are in advanced stages of development. We focus on the mechanisms of action as well as the efficacy and safety profiles of these devices. Many of these devices are placed endoscopically, which provides gastroenterologists with exciting opportunities for treatment.

Novel developments in vagal afferent nutrient sensing and its role in energy homeostasis

Vagal afferent neurons (VANs) play an important role in the control of food intake by signaling nutrient type and quantity to the brain. Recent findings are broadening our view of how VANs impact not only food intake but also energy homeostasis. This review focuses exclusively on studies of the vagus nerve from the past 2 years that highlight major new advancements in the field. We firstly discuss evidence that VANs can directly sense nutrients, and we consider new insights into mechanisms affecting sensing of gastric distension and signaling by gastrointestinal hormones ghrelin and GLP1. We discuss evidence that disrupting vagal afferent signaling increases long-term control of food intake and body weight management, and the importance of this gut-brain pathway in mediating beneficial effects of bariatric surgery. We conclude by highlighting novel roles for vagal afferent neurons in circadian rhythm, thermogenesis, and reward that may provide insight into mechanisms by which VAN nutrient sensing controls long-term control of energy homeostasis.