Obesity is a chronic disease.1 This simple statement has generated an extraordinary amount of controversy in recent years, despite the fact that obesity clearly meets the criteria described by the U.S. National Center for Health Statistics, which defines a chronic disease as one lasting three months or more, one that cannot be prevented by vaccines or cured by medication, and one that does not simply disappear. In 2013, the American Medical Association (AMA) declared obesity to be a chronic disease in a statement opposing its own Council on Science and Public Health, which had avoided issuing a similar recommendation based on the simplistic and flawed measure of the disease in terms of body mass index (BMI). The AMA’s final resolution stated, “The suggestions that obesity is not a chronic disease but rather a consequence of a chosen lifestyle exemplified by overeating and/or inactivity is equivalent to suggesting that lung cancer is not a disease because it was brought about by individual choice to smoke cigarettes.”2
Obesity is not just a chronic disease; rather, it is a chronic, multifactorial disease caused by a derangement of the metabolism. It is a complex disease process that continues to require intensive study and requires a variety of therapies to be controlled. Attempts to differentiate bariatric surgery and metabolic surgery have been made, but current evidence and opinion support the use of the term bariatric metabolic surgery to best describe these surgical interventions.
The metabolic problems associated with obesity have been a primary focus of the field of bariatric metabolic surgery for years. In the last decade, though, our understanding of how surgical interventions favorably alter the metabolism has increased. This knowledge allows us to “medicalize” the disease of obesity and to discuss it as we would any other chronic disease rather than to limit the discussion to individual behavior and willpower. In fact, one of the greatest barriers to the treatment of obesity is the societal bias that patients with obesity lack the will or discipline to overcome this disease. Patients internalize this bias and attempt to treat the disease on their own rather than seek medical help, as they would for other diseases. While these barriers still exist, the growing body of evidence and more accurate messaging around the complexities of obesity are slowly gaining a foothold within the medical community and the public.
This article reviews the range of metabolic procedures being performed, examines the long-term outcomes of each, and reviews the safety profile of bariatric metabolic procedures since the establishment of large data registries and accreditation programs.
A dynamic field
The field of bariatric metabolic surgery has always been dynamic. As outlined in a separate article by Henry Buchwald, MD, PhD, FACS, and colleagues published in the January issue of the Bulletin,* many metabolic surgical procedures have been tried and abandoned over the last seven decades. Even in the last 30 years, there has been significant volatility in the types of operations performed (see Figure 1).3 As we have gained a better understanding of the need for long-term follow-up by a multidisciplinary team, we have also developed a better appreciation for the challenges inherent in treating a chronic disease with a single operation. Because some patients will not respond well to certain interventions or may have recurrent disease in the long term, support is growing for the application of additional surgical, endoscopic, or medical interventions as adjuvant treatment for the disease. Similar to the approach to recurrent cancer and many other chronic diseases, the cause of recurring obesity after surgery should not be laid solely at the feet of the patient as a “failure,” but should be viewed by the medical community as signaling the need for additional therapy. Modifiable risk factors must be addressed for every chronic disease, but the biologic and physiologic components are equally important. Many of these secondary interventions may augment or improve the metabolic effects of the primary procedure.
The most commonly performed bariatric procedure in the U.S. and the world is the laparoscopic sleeve gastrectomy (SG), representing 58 percent of all bariatric metabolic procedures performed in 2016 (see Table 1).3 The path to the widespread acceptance of SG was relatively slow. When the first research articles on SG were published in 2003, the procedure was considered a bail-out strategy for duodenal switch (DS) cases where the operating surgeon judged completion in one stage to be overly risky or a first-stage procedure to reduce BMI and patient risk before a definitive gastric bypass or DS procedure.4 Initially, SG was rarely performed, and in 2007 the American Society for Metabolic and Bariatric Surgery (ASMBS) published the first SG position statement summarizing the limited evidence at that time. The statement endorsed SG only as a staging procedure. By 2009, sufficient medium-term evidence was available to support SG as a safe primary procedure. In 2012, the ASMBS published an updated position statement that included enough long-term data (>5 years) that the procedure was fully endorsed as safe and durable.5-7
Table 1. ASMBS estimates of the number of surgical procedures performed in the U.S.
Today, an abundance of evidence supports the safety and durability of SG. In a recent update of its SG position paper, the ASMBS provided a systematic review of the relevant literature that included 39 published studies with greater than five-year follow-up of 2,248 patients.5 The average long-term percentage excess weight loss ranged from 37 percent to 86 percent in this review. In individual studies with larger samples (n≥100), long-term excess weight loss ranged from 61 percent to 88 percent (see Table 2).8-14
Table 2. Selected studies (n>100) of long-term follow-up after sleeve gastrectomy
SG results in more than just a reduction in stomach capacity and is thus recognized as a metabolic operation. The primary metabolic effects of SG include immediate and sustained reduction in ghrelin,15 which decreases appetite and pre-meal hunger and increases gut hormone production in the distal bowel, presumably related to more rapid gastric emptying and nutrient transit. Studies have clearly demonstrated postprandial elevations in two important peptides produced in the L cells of the distal bowel, PYY 3-36 and GLP-1.16,17 PYY 3-36 acts as part of the “ileal brake” on the hypothalamus to induce satiety and decrease hunger after eating. GLP-1 is an incretin hormone that stimulates pancreatic beta cells to produce insulin in response to a meal, an effect that is likely one of the primary weight-loss independent mechanisms that make SG an effective operation for the treatment of type 2 diabetes. Remission rates of metabolic comorbidities and weight loss after SG are similar to or slightly less than those seen with gastric bypass one to three years after surgery.18-20
SG effectively treats hypertension, hyperlipidemia, and type 2 diabetes. In the Surgical Treatment and Medications Potentially Eradicate Diabetes Efficiently (STAMPEDE) trial, patients were randomized to intensive medical therapy (IMT) alone versus IMT and SG versus IMT and Roux-en-Y gastric bypass (RYGB) (see Table 3). At five years, surgical patients had significantly better glycemic control and higher rates of tight control (HbA1C ≤6) than IMT alone. SG and RYGB showed similar rates of achieving the primary endpoint of HbA1C ≤6; however, more SG than RYGB patients required supplementary medication to achieve that level of control.18 This finding suggests that although the metabolic effects of SG on diabetes are good, they are neither as powerful nor durable as the effects of RYGB. This outcome may be related to the additional effect of another anti-diabetes mechanism of the gastric bypass, which is the exclusion of nutrient flow through the duodenum and proximal bowel.
Table 3. Randomized trials comparing SG and RYGB
RYGB is the bariatric procedure with the longest active history. Although it has taken various forms over the years and continues to be performed around the world both as a Roux-en-Y as well as in a loop configuration, most of the literature reports the results of the RYGB. According to the most recent estimates, RYGB comprised 19 percent of the bariatric metabolic procedures performed in 2016 (see Table 1). The relatively rapid decline in the number of RYGB operations performed in recent years (37 percent in 2011) is directly related to the increasing number of SGs performed.
RYGB has proven to have sustained, long-term weight loss and metabolic effects. In the last five years, 38 RYGB series with more than five years of follow-up have been published. According to a review performed by the ASMBS Clinical Issues Committee in preparation for a statement on the durability of bariatric procedures, the long-term weight loss after RYGB ranged from 50 percent to 72 percent excess weight loss; 19 percent to 35 percent total weight loss was reported over the long term. Outcomes of studies demonstrating the durability of RYGB beyond five years with more than 100 patients at follow-up are shown in Table 4.21-39
Table 4. Long-term outcomes of gastric bypass with follow-up >5 years (n>100)
As previously stated, several metabolic mechanisms affect the efficacy of RYGB. Many of the individual components of the gastric bypass procedure have served as targets of therapy for novel endoscopic devices or medications. At least five different components contribute to the metabolic effects of this operation, including gastric volume reduction (exclusion of ghrelin-producing cells); caloric restriction; partial vagotomy; exclusion of nutrient flow through the distal stomach, duodenum, and proximal jejunum; and the rapid nutrient transit into the distal bowel. The relative contribution of each of these mechanisms in the overall metabolic effect is unknown; yet, ample animal and human data suggest that rapid transit of nutrients into the distal bowel, and duodenal exclusion, may drive most of the weight loss-independent metabolic effects of RYGB.40 Other potential mechanisms, such as increased bile acid circulation and changes in the gut microbiome, are being studied.41
The effects of gastric bypass on remission or improvement of type 2 diabetes have been repeatedly demonstrated over the last 30 years. Overall remission rates are 80 percent, but individual phenotypes demonstrate variable responses to the operation. Patients with long-standing diabetes or who require insulin at the time of surgery (both indicators of poor beta-cell reserve) are less likely to achieve remission but still may enjoy better diabetes control and fewer medications.18,23,42,43 Diabetes recurs in some patients long after gastric bypass. Most long-term studies demonstrate 50 percent to 60 percent remission rates beyond five years—possibly as a result of some weight regain or a progression of this chronic disease that was put into remission for several years.44,45 Whatever the length of a period of remission, it may extend the onset for that length of time of chronic type 2 diabetes ocular or vascular complications. The STAMPEDE trial confirmed that gastric bypass patients had improved insulin sensitivity compared with SG patients and medical patients, which correlated with a significant decrease in truncal fat after bypass that was not found after SG.46 Long-term remission rates of other metabolic diseases, such as hypertension and hyperlipidemia, are reported to be in the range of 40 percent to 60 percent. Long-term survival for patients who underwent gastric bypass improves by 30 percent to 40 percent compared with similar patients who did not undergo surgery. This effect is primarily the result of decreased cardiovascular and cancer risk.47-49 At present, 11 randomized trials demonstrate the superiority of bariatric surgery over medical treatment for diabetes.50 In addition, three randomized clinical trials compare safety, weight loss, gastroesophageal reflux, and quality of life after SG and RYGB (see Table 2).18,19,51
BPD and DS
The biliopancreatic diversion (BPD) and DS operations are the most potent metabolic procedures performed today (see Table 5).52-56 The combination of a partial gastrectomy with a very long biliopancreatic limb and relatively short common channel appears to promote significant weight loss and metabolic improvements beyond what is typically seen with RYGB.57 In one randomized trial comparing BPD with RYGB for the treatment of type 2 diabetes, neither preoperative BMI nor weight loss at five years predicted diabetes remission, which suggests that the weight loss-independent metabolic effects of BPD and DS exceed those of the proximal gastric bypass.58 Despite these powerful and durable effects on diabetes and metabolic disease, DS represents only about 1 percent of the procedures performed in the U.S. This low penetration rate of a highly effective operation is likely due to the increased technical demands of the procedure, its significantly higher risk of technical complications, and its potential to induce long-term micro- and/or macro-nutrient deficiencies.
Table 5. Long-term outcomes of biliopancreatic diversion and duodenal switch (n >100)
Laparoscopic adjustable gastric band
Laparoscopic adjustable gastric banding (LAGB) has been used worldwide for several decades and was approved for use in the U.S. in 2001. While implantation of the device does not directly result in metabolic changes, the weight loss associated with LAGB does result in metabolic improvements. It is clear that clinically significant weight loss after LAGB results in decreased inflammation, cardiovascular risk factors, and other obesity-related comorbidities. Specifically, randomized trials have shown LAGB to be superior to medical therapy for achieving remission of type 2 diabetes and metabolic syndrome.59-61 Despite this evidence that the successful LAGB patient will have metabolic improvement long term, this procedure has no weight loss-independent effect on diabetes or metabolic syndrome, and LAGB is not considered a metabolic procedure.
The field of bariatric metabolic surgery is dynamic and continues to change based on the emergence of new procedures with improved risk/benefit profiles. The most commonly performed metabolic operations performed today are the SG, RYGB, and DS. Each of these procedures has inherent risks, but all have a very good safety profile, and the choice of procedure for a specific patient is made based on a specific patient’s metabolic burden, weight loss expectations, and the surgeon’s experience. Ample long-term (>5 year) evidence supports the efficacy of these operations for the treatment of obesity and its related metabolic diseases.62 Quality of life also improves for patients who undergo metabolic operations—an additional durable benefit.
In summary, the safety, efficacy, and durability of bariatric metabolic surgery are supported by a large body of evidence that includes numerous randomized trials. These interventions should be routinely offered as part of the continuum of care for every patient with obesity and metabolic disease.
This work was supported by the American College of Surgeons (ACS). The authors declare that they have no relevant conflict of interest.
We are grateful to the ACS for their generous sponsorship of the Metabolic Surgery Symposium and associated journal publication development. We thank Jane N. Buchwald, chief scientific research writer, Medwrite Medical Communications, Maiden Rock, WI, for manuscript editing and publication coordination. And we thank Patrick Beebe and Donna Coulombe, ACS Executive Services, for their expert organization of the Metabolic Surgery Symposium.
*Buchwald H, Fobi MAL, Herron D, Brethauer S. Definition and history of bariatric surgery. Bull Am Coll Surg. 2019;104(1):44-52. Available at: bulletin.facs.org/2019/01/definition-and-history-of-metabolic-surgery/. Accessed January 16, 2019.
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