Review
Effects of Bariatric Surgery on Energy Homeostasis

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Abstract

Bariatric surgery represents the most efficient therapy for severe obesity. It reduces the size of fat stores or the amount of body fat gain. The bariatric surgery procedures currently used include Roux-en-Y gastric bypass and sleeve gastrectomy, which are the most commonly performed procedures. Other procedures are laparoscopic adjustable gastric banding and biliopancreatic diversion. The latter represents the most effective surgery for treatment of severe obesity as well as type 2 diabetes. Bariatric surgery reduces energy intake by restricting the size of the stomach reservoir and causing malabsorption, as in the case of biliopancreatic diversion. The present article provides an overview of the literature on the effects of bariatric surgery on energy homeostasis. Accumulated evidence has indicated that the effects of bariatric surgery on energy balance can encompass complex components including effects on the corticolimbic appetitive network, with modulatory effects exerted through changes in gastrointestinal hormones, bile acid production and microbiota composition. The reorganization of the gastrointestinal tract has been shown to reduce the rewarding effects of palatable food and impulsive eating, while elevating anorexigenic hormones glucagon-like peptide 1 and peptide tyrosine tyrosine to stimulate the production of bile acids and normalize the obesogenic gut microbiota. Bariatric surgery could also increase energy expenditure, which represents, like energy intake, a key component of the energy balance equation.

Résumé

La chirurgie bariatrique représente le traitement le plus efficace de l'obésité sévère. Elle réduit les réserves de graisse ou l'accumulation de tissu adipeux. Parmi les interventions chirurgicales courantes de l'obésité, le pontage gastrique avec anse en Y de Roux et la gastrectomie longitudinale sont les interventions les plus fréquemment effectuées. Les autres interventions sont l'anneau de gastroplastie ajustable implanté par laparoscopie et la dérivation biliopancréatique. Cette dernière représente l'intervention chirurgicale la plus efficace pour le traitement de l'obésité ainsi que pour le diabète de type 2. La chirurgie bariatrique réduit l'apport énergétique en réduisant la taille de l'estomac et, dans le cas de la dérivation biliopancréatique, en provoquant une malabsorption. Le présent article donne un aperçu de la littérature sur les effets de la chirurgie bariatrique sur l'homéostasie énergétique. Les données probantes accumulées ont indiqué que les effets de la chirurgie bariatrique sur le bilan énergétique peut englober des éléments complexes, à savoir les effets sur le réseau corticolimbique impliqué dans l'appétit et les effets modulateurs exercés par les changements dans les hormones gastro-intestinales, la production des acides biliaires et la composition du microbiote. Il a été démontré que la réorganisation du tractus gastro-intestinal réduit les effets de récompense des aliments palatables et de l'alimentation impulsive, alors que l'élévation de l'hormone GLP–1 (glucagon-like peptide–1) à effet anorexigène et du peptide tyrosine-tyrosine stimule la production des acides biliaires et normalise le microbiote intestinal obésogène. La chirurgie bariatrique pourrait également augmenter la dépense énergétique, qui représente, comme l'apport énergétique, un élément essentiel de l'équation du bilan énergétique.

Introduction

The prevalence of obesity (body mass index [BMI]≥30 kg/m2) has considerably increased over the last decades. Globally, more than 1 of 10 adults is now obese (http://www.who.int/mediacentre/factsheets/fs311/en/). Even though a slowing of the increase in obesity prevalence has been reported (1), obesity remains a significant health issue. In fact, the prevalence of excess weight remains very high in most industrialized countries, and the prevalence of morbid, or severe, obesity (BMI >40 kg/m2) continues to rise. Obesity, in particular in its severe forms (morbid and visceral), is associated with a plethora of sequelae (https://www.nhlbi.nih.gov/health/health-topics/topics/obe/risks), leading to a major socioeconomic burden.

Complex gene-environment interactions underlie obesity (2); the obesogenic environment in which we live, which facilitates a sedentary lifestyle and overeating through marketing and the availability of energy-dense foodstuffs, proves to be particularly obesity inducing in individuals who are genetically predisposed to a positive energy balance. The heritability of excess fat deposition, which is estimated to be between 40% and 70 % from most biometric studies (e.g. family, adoption and twin studies), is noticeable (3). Predisposition to obesity is admittedly polygenic, and genetic variations that promote obesity are likely to be associated with obesogenic genes. Those genes are involved in modern lifestyle–induced obesity by contributing to overeating, sedentary lifestyle and other obesity-promoting behaviours (4). The modern lifestyle is also responsible for producing epigenetic effects that could contribute to obesity 5, 6, 7. Obesity-related epigenetic effects cannot only be induced or reversed during life but can also be passed through generations (8). The environment in which we live is also likely to alter the gut microbiota, rendering it obesogenic (9).

The high prevalence of obesity, together with the awareness of its detrimental health effects and its socioeconomic burden, has stimulated research on obesity. Part of this research has involved the medical treatment of the condition, in particular, the effects of bariatric surgery, which is recognized as the most efficient treatment for severe obesity (10). Bariatric surgery has also been shown to cure several obesity-related comorbidities, including type 2 diabetes, dyslipidemia, hypertension and sleep apnea, and to improve mental health. Noticeable progress has been made in better understanding of how this surgery cures obesity. There is growing evidence that bariatric surgery influences energy balance regulation in various ways 11, 12, 13, 14. This short article provides an overview of the effects of bariatric surgery on energy homeostasis.

Section snippets

Bariatric Surgery and Obesity

The bariatric surgery procedures that are used to treat severe obesity include gastric banding procedures, mainly laparoscopic adjustable gastric banding, Roux-en-Y gastric bypass (RYGB), sleeve gastrectomy (SG) and biliopancreatic diversion (BPD) (15). Currently, the most commonly performed procedures are RYGB and SG (15), which have been described as restrictive obesity procedures because they limit the amount of food that can be eaten. RYGB restricts the stomach to a small (generally less

Bariatric Surgery and Energy Balance

As stated previously, bariatric surgery constitutes the most efficacious treatment for severe obesity. The BPD-DS has proven to be particularly efficacious, with a loss of 83%±14% of excess body weight observed at 36 months (31). Furthermore, a loss of 40.7%±10.8% of excess body weight has been observed 10 years after laparoscopic BPD-DS in patients with a BMI>50 kg/m2 (32). As mentioned previously, weight loss after bariatric surgery primarily consists of fat mass loss. In high-fat–fed obese

Bariatric Surgery and the Regulation of Energy Balance

In addition to mechanically restricting eating or producing energy malabsorption, bariatric procedures, in particular those that reorganize the small bowel, have been proven to affect energy balance by acting on the regulatory processes governing energy balance 11, 47, 48. Energy balance regulation is achieved through highly coordinated communications between neurobiologic circuits and peripheral homeostatic pathways that control food intake and energy expenditure (49). It involves

Conclusion

Bariatric surgery reduces the size of fat stores and the amount of body fat gain. It represents the most efficient therapy for severe obesity, and it also cures type 2 diabetes. Bariatric surgery procedures reorganize the gastrointestinal tract and thereby alter the gastrointestinal physiology in such a way that effects on energy homeostasis go beyond those caused by mechanical restriction of the stomach or gut malabsorption. Evidence keeps accumulating that the effects of bariatric surgery on

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