Approach to Weight Management in GI Practice
Introduction
The majority of patients in the United States are now overweight or obese, and as gastroenterologists we treat a number of conditions that are caused or worsened by obesity.1 Cirrhosis related to metabolic associated fatty liver disease (MAFLD) is now a leading indication for liver transplantation in the US2 and obesity is a clear risk factor for all major malignancies of the GI tract, including esophageal, gastric cardia, pancreatic, liver, gallbladder, colon, and rectum.3 Obesity is associated with dysbiosis and impacts barrier function: increasing permeability, abnormal gut bacterial translocation, and inflammation.4 It is more common than malnutrition in our patients with inflammatory bowel disease (IBD), where it impacts response to biologic drugs, increases the technical difficulty of surgeries, such as IPAA, and is associated with worse surgical outcomes.5 Furthermore, patients with obesity may be less likely to undergo preventative cancer screenings and are at increased risk related to sedation for endoscopic procedures.6 With over 40% of Americans suffering from obesity, and increasingly effective treatments available,
Understanding the Mechanisms of Obesity
There are complex orexigenic and anorexigenic brain pathways in the hypothalamus which control global energy balance.7 Obesity results when energy intake exceeds energy expenditure. While overeating and a sedentary lifestyle are commonly blamed, there are a number of elements that contribute, including genetics, medical conditions, medications, psychosocial factors, and environmental components. For example, sleep loss contributes to weight gain by several mechanisms including increasing ghrelin and decreasing leptin levels, thereby increasing hunger and appetite, as well as by decreasing insulin sensitivity and increasing cortisol. Subjects exposed to sleep deprivation in research settings take in 550 kcal more the following day.8 Medications used commonly in GI practice including corticosteroids, antihistamines, propranolol, and amitriptyline, are obesogenic9 and cannabis can impact hypothalamic pathways to stimulate hunger.10
When patients diet or exercise to lose weight, as we have traditionally advised, there are strong hormonal changes and metabolic adaptations that occur to preserve the defended fat mass or “set point.” Loss of adipose tissue results in decreased production of leptin, a hormone that stimulates satiety pathways and inhibits orexigenic pathways, greatly increasing hunger and cravings. Increases in ghrelin production by the stomach decreases perceptions of fullness. With weight loss, energy requirements decrease, and muscles become more efficient, meaning fewer kcal are needed to maintain bodily processes.11 Eventually a plateau is reached, while motivation to diet and restraint around food wane, and hedonistic (reward) pathways are activated. These powerful factors result in the regain of lost weight within one year in the majority of patients.
Implementing Weight Management into GI Practice
Given the stigma and bias around obesity, patients often feel shame and vulnerability around the condition. It is important to have empathy in your approach, asking permission to discuss weight and using patient-first language (e.g. “patient with obesity” not “obese patient”). While BMI is predictive of health outcomes, it does not measure body fat percentage and may be misleading, such as in muscular individuals. Other measures of adiposity including waist circumference and body composition testing, such as with DEXA, may provide additional data. A BMI of 30 or above defines obesity, though newer definitions incorporate related symptoms, organ disfunction, and metabolic abnormalities into the term “clinical obesity.”12 Asian patients experience metabolic complications at a lower BMI, and therefore the definition of obese is 27.5kg/m2 in this population.
Begin by taking a weight history. Has this been a lifelong struggle or is there a particular life circumstance, such as working a third shift or recent pregnancy which precipitated weight gain? Patients should be asked about binge eating or eating late into the evening or waking at night to eat, as these disordered eating behaviors are managed with specific medications and behavioral therapies. Inquire about sleep duration and quality and refer for a sleep study if there is suspicion for obstructive sleep apnea. Other weight-related comorbidities including hyperlipidemia, type 2 diabetes mellitus (T2DM), and MAFLD should be considered and merit a more aggressive approach, as does more severe obesity (class III, BMI ≥40). Questions about marijuana and alcohol use as well as review of the medication list for obesogenic medications can provide further insight into modifiable contributing factors.
Pillars of Weight Management
The internet is awash with trendy diet recommendations, and widespread misconceptions about obesity management are even ingrained into how physicians approach the disease. It is critical to remember that this is not a consequence of bad choices or lack of self-control. Exercise alone is insufficient to result in significant weight loss.13 Furthermore, whether it is through low fat, low carb, or intermittent fasting, weight loss will occur with calorie deficit.14 Evidence-based diet and lifestyle recommendations to lay the groundwork for success should be discussed at each visit (see Table 1). The Mediterranean diet is recommended for weight loss as well as for several GI disorders (i.e., MAFLD and IBD) and is the optimal eating strategy for cardiovascular health.15 Patients should be advised to engage in 150 minutes of moderate exercise per week, such as brisk walking, and should incorporate resistance training to build muscle and maintain bone density.
Anti-obesity Medications
There are a number of medications, either FDA approved or used off label, for treatment of obesity (see Table 2).16 All are indicated for patients with a BMI of ≥ 30 kg/m2 or for those with a BMI between 27-29 kg/m2 with weight-related comorbidities and should be used in combination with diet and lifestyle interventions. None are approved or safe in pregnancy. Mechanisms of action vary by type and include decreased appetite, increased energy expenditure, improved insulin sensitivity, and interfere with absorption.
The newest and most effective anti-obesity medications (AOM), the glucagon-like peptide-1 receptor agonists (GLP-1 RA) are derived from gut hormones secreted in the distal small bowel and colon in response to a meal, which function to delay gastric emptying, increase insulin release from the pancreas, and reduce hepatic gluconeogenesis. Central nervous system effects are not yet entirely understood, but function to decrease appetite and increase satiety. Initially developed for treatment of T2DM, observed weight reduction in patients treated with GLP-1 RA led to clinical trials for treatment of obesity. Semaglutide treatment resulted in weight reduction of 16.9% of total body weight (TBW), and one third of subjects lost ≥ 20% of TBW.17 Tirzepatide combines GLP-1 RA and a gastric inhibitory polypeptide (GIP) receptor agonist, which also has an incretin effect and functions to slow gastric emptying. In the pivotal SURMOUNT trial, approximately 58% of patients achieved ≥20% loss of TBW18 with 15mg weekly dosing of tirzepatide. This class of drugs is a logical choice in patients with T2DM and obesity. Long-term treatment appears necessary, as patients typically regain two-thirds of lost weight within a year after GLP-1 RA are stopped.
Based on tumors observed in rodents, GLP-1 RA are contraindicated in patients with a personal or family history of multiple endocrine neoplasia type 2 (MEN II) or medullary thyroid cancer. These tumors have not been observed in humans treated with GLP-1 RA. They should be used with caution in patients with history of pancreatitis, gastroparesis, or diabetic retinopathy, though a recent systematic review and meta-analysis suggests showed little to no increased risk for biliary events from GLP-1 RA.19 Side effects are most commonly gastrointestinal in nature (nausea, reflux, constipation or diarrhea) and are typically most severe with initiation of the drug and with dose escalation. Side effects can be mitigated by initiating these drugs at lowest doses and gradually titrating up (every four weeks) based on effectiveness and tolerability. Antisecretory, antiemetic, and laxative medications can also be used to help manage GLP-1 RA related side effects.
There is no reason to escalate to highest doses if patients are experiencing weight loss and reduction in food cravings at lower doses. Both semaglutide and tirzepatide are administered subcutaneously every seven days. Once patients have reached goal weight, they can either continue maintenance therapy at that same dose/interval, or if motivated to do so, may gradually reduce the weekly dose in a stepwise approach to determine the minimally effective dose to maintain weight loss. There are not yet published maintenance studies to guide this process. Currently the price of GLP-1 RA and inconsistent insurance coverage make them inaccessible to many patients. The manufacturers of both semaglutide and tirzepatide offer direct to consumer pricing and home delivery.
Bariatric Surgery
In patients with higher BMI (≥35kg/m2) or those with BMI ≥30kg/m2 and obesity-related metabolic disease and the desire to avoid lifelong medications or who fail or are intolerant of AOM, bariatric options should be considered.20 Sleeve gastrectomy has become the most performed surgery for treatment of obesity. It is a restrictive procedure, removing 80% of the stomach, but a drop in circulating levels of ghrelin afterwards also leads to decreased feelings of hunger. It results in weight loss of 25-30% TBW loss. It is not a good choice for patients who suffer from severe GERD, as this typically worsens afterwards; furthermore, de novo Barrett’s has been observed in nearly 6% of patients who undergo sleeve gastrectomy.21
Roux-en-Y gastric bypass is a restrictive and malabsorptive procedure, resulting in 30-35% TBW loss. It has beneficial and immediate metabolic effects, including increased release of endogenous GLP-1, which leads to improvements in weight-related T2DM. The newer single anastomosis duodenal-ileal bypass with sleeve gastrectomy (SADI-S) starts with a sleeve gastrectomy, making a smaller tube-shaped stomach. The duodenum is divided just after the stomach and then a loop of ileum is brought up and connected to the stomach (see Figure 1). This procedure is highly effective, with patients losing 75-95% of excess body weight and is becoming a preferred option for patients with greater BMI (≥50kg/m2). It is also an option for patients who have already had a sleeve gastrectomy and are seeking further weight loss. Because there is only one anastomosis, perioperative complications, such as anastomotic leaks, are reduced. The risk of micronutrient deficiencies is present with all malabsorptive procedures, and these patients must supplement with multivitamins, iron, vitamin D, and calcium.
Endoscopic Therapies
Endoscopic bariatric and metabolic therapies (EBMTs) have been increasingly studied and utilized, and this less invasive option may be more appropriate for or attractive to many patients. Intragastric balloons, which reduce meal volume and delay gastric emptying, can be used short term only (six months) resulting in loss of about 6.9% of total body weight (TBW) greater than lifestyle modification (LM) alone, and may be considered in limited situations, such as need for pre-operative weight loss to reduce risks in very obese individuals.22
Endoscopic gastric remodeling (EGR), also known as endoscopic sleeve gastrectomy (ESG), is a purely restrictive procedure in which the stomach is cinched to resize and reshape using an endoscopic suturing device (see Figure 2).23 It is an option for patients with class 1 or 2 obesity, with data from a randomized controlled trial in this population demonstrating mean percentage of TBW loss of 13.6% at 52 weeks compared to 0.8% in those treated with LM alone.24 A recent meta-analysis of 21 observational studies, including patients with higher BMIs (32.5 to 49.9 kg/m2) showed pooled average weight loss of 17.3% TBW at 12 months with EGR.22 This procedure has potential advantages of fewer complications, quicker recovery, and much less new-onset GERD compared to laparoscopic sleeve gastrectomy. Furthermore, it may be utilized in combination with AOMs to achieve optimum weight loss and metabolic outcomes.25,26 Potential adverse events include abdominal pain, nausea and vomiting (which may be severe), as well as rare instances of intra/extra luminal bleeding or abdominal abscess requiring drainage.22
Recent joint American/European Gastrointestinal Endoscopy guidelines suggest the use of EBMTs plus lifestyle modification in patients with a BMI of ≥ 30 kg/m2, or with a BMI of 27.0-29.9 kg/m2 with at least 1 obesity-related comorbidity.22 Small bowel interventions including duodenal-jejunal bypass liner and duodenal mucosal resurfacing are being investigated for patients with obesity and type 2 diabetes but not yet commercially available.
Conclusion
Given the overlap of obesity with many GI disorders, it is entirely appropriate for gastroenterologists to consider it worthy of aggressive treatment, particularly in patients with MAFLD and other serious weight related comorbidities. With a compassionate and empathetic approach, and a number of highly effective medical, endoscopic, and surgical therapies now available, weight management has the potential to be extremely rewarding when implemented in GI practice.
Dr. Kelly is based in the Department of Medicine, Division of Gastroenterology, Brigham and Women’s Hospital, and Harvard Medical School, both in Boston, Massachusetts. She serves on the clinical advisory board for OpenBiome (unpaid) and has served on an advisory board for Eli Lilly and Company.
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