Bariatric Surgery and the Role of the Clinical Endocrinologist
Posted: 11/08/2011; Endocrine Practice. 2011;17(5):788-797. © 2011 American Association of Clinical Endocrinologists
Abstract and Introduction
Objective: To discuss the emerging roles of bariatric surgery and clinical endocrinology within the context of obesity and diabetes mellitus comprehensive care plans and cost-effective strategies.
Methods: Relevant literature is reviewed and clinical cases are presented.
Results: The global obesity epidemic poses many challenges to clinical endocrinologists and has fomented a coordinated effort among specialists to revolutionize management paradigms. Technologic innovation drives the need for accelerated learning and research efforts in bariatric surgery. The national shortage of physicians with expertise in nutritional medicine compounds the management problems for this expanding patient population. Certain issues merit continued attention and research, such as gastric banding for mild obesity, surgery for treatment of diabetes, sleeve gastrectomy, and nutritional and metabolic consequences.
Conclusion: Clinical endocrinologists should have a central role in the perioperative decision-making for patients undergoing bariatric surgery.
The global obesity epidemic has incited innovation and technology to advance at such a great pace that many subspecialties have had to reengineer and reprioritize their efforts in metabolic medicine. Perhaps the best example is that of bariatric surgery and the role of the clinical endocrinologist in perioperative care. In 2008, the American Association of Clinical Endocrinologists (AACE), The Obesity Society, and the American Society for Metabolic and Bariatric Surgery published evidence-based clinical practice guidelines (CPG) on the perioperative nutritional, metabolic, and nonsurgical support of patients undergoing bariatric surgery. Within these CPG, also endorsed by the American Society of Parenteral and Enteral Nutrition, are 164 specific recommendations providing a comprehensive and collaborative effort to support clinical decision-making. Even though this resource was a welcomed addition to the armamentarium for bariatric surgery perioperative care, it also identified a potential weakness: that many patients undergoing bariatric surgery were not receiving expert medical nutrition care and that the number of available physicians with expertise in nutritional medicine was probably insufficient to care for the expected number of patients. Because clinical endocrinologists receive formal training in metabolic disorders and some training in clinical nutrition, AACE has incorporated plenary sessions, workshops, and “Meet The Experts” sessions on bariatric surgery since 2007 at their annual meetings. This article will review contemporary trends in bariatric surgery and then present 4 controversial aspects that have emerged since the 2008-published CPG. The discussions will focus on recent publications, most in the past 1 to 2 years, and have particular applicability to the role of the clinical endocrinologist in perioperative decision-making.
Setting the Stage: Seminal Events Since 2008
Various white papers have been published since 2008 spanning the breadth of interest related to bariatric surgery (Table 1). Even though the utility of these authoritative documents has been called into question lately based on differences in methodology and final recommendations, they have succeeded in drawing attention to 3 important trends that will frame current controversies.
First, the increased trend in obesity prevalence rates across ages, social classes, and cultures leads to greater cardiovascular disease (CVD), economic burden, and all-cause mortality. Type 2 diabetes mellitus (T2DM) and obesity are inexorably intertwined. The T2DM prevalence is now 9.6% in the United States and increases with higher body mass index (BMI) weight classes. There is also an increased prevalence of obesity with T2DM—now 49.1% in the United States compared with 32.2% to 35.5% in patients without T2DM.[17,18] The natural extrapolation of this relationship is that interventions to prevent and treat the state of being overweight or obese can have salutary effects on the epidemiology of T2DM.
Bariatric surgery appears to be safe and effective, but may be prohibitively expensive for application to a clinical problem with this global magnitude. However, strategies can be developed for the algorithmic implementation of bariatric surgery based on an improved understanding of the pathophysiology and the social environment, rather than on media-based claims and attitudes. For instance, the impact of environment can be clarified by analyzing dietary patterns. Consuming a diet rich in fruits, vegetables, whole grains, and reduced-fat dairy products protects against the development of T2DM. It has therefore been suggested that the medical community must develop an integrative delivery network or metabolic service line; that is, to continue to pursue comprehensive preventive strategies to address the dysmetabolism epidemic across all risk strata while continuing to incorporate focused guidelines for the appropriate use of aggressive disease management paradigms, such as bariatric surgery.
Second, the trend toward more rigorous governmental scrutiny of new antiobesity drugs, particularly with respect to CVD risks, has resulted in more limited therapeutic options for obese patients. The frustrations with intensive lifestyle intervention, coupled with the paucity of antiobesity drugs with proven long-term safety and effectiveness, has engendered an innovative, technology-driven setting (Table 2). Unfortunately, accelerating the pace of innovation, acceptance, and incorporation into white paper materials produces unexpected downstream clinical problems and ethical dilemmas. This raises the question of where on the learning curve is the “sweet-spot” for widespread implementation? In other words, where do the concerns about inexperience (early on learning curve) intersect with best practice (late on the learning curve)? Furthermore, which patients are most appropriate candidates for these procedures and which procedures are most appropriate for your patient?
Third, because there are an increasing number of patients undergoing bariatric surgery who have varying degrees of preoperative and postoperative nutritional and metabolic disorders,[1,32–36] there is a greater societal need for physicians specializing in nutritional medicine. The shortage in physician nutrition experts has been addressed and will require a concerted effort among stakeholders, including clinical endocrinologists, at educational and clinical practice levels.[37,38] Thus, clinical endocrinologists should become aware of the contemporary challenges in the surgical management of obesity, and to that end, 4 clinical problems will be presented.
Clinical Problems in Bariatric Surgery
Problem 1: Should Patients With Only Mild Obesity be Referred for Laparoscopic Adjustable Gastric Banding? Is There a Role forPrevention of Severe Obesity?
In the 2008 AACE/The Obesity Society/American Society for Metabolic and Bariatric Surgery CPG on bariatric surgery, recommendations R1 through R4 provide the criteria for patient eligibility. This is summarized in recommendations R1 and R2 as patients with a BMI greater than 40 kg/m2 (or 35 kg/m2 with an obesity-related comorbidity) in whom surgery would not be associated with excessive risk. In recommendation R3, it is stated that “insufficient data are available to recommend bariatric surgery for patients with a BMI < 35 kg/m2“. However, in subsequent years, sufficient data[39–44] were presented to the US Food and Drug Administration that led to the approval of more relaxed criteria (BMI of at least 30 kg/m2 with an obesity-related comorbidity; mild obesity) for laparoscopic adjustable gastric banding (LAGB). Varela and Frey demonstrated comparable safety and effectiveness of LAGB between mildly obese and more severely obese patients. However, the question remains: even though patients are now eligible for LAGB at lower BMI levels, at what BMI would you actually recommend LAGB? The approach to this question is framed by considerations of the patient’s behavior toward intensive lifestyle intervention and likelihood of progress; severity of the patient’s metabolic profile; risk for obesity-related comorbidities, CVD, and mortality; and safety and effectiveness of the resources available for that patient. At this point, many physicians have bought-in to this concept of prevention of severe obesity based on certain weight gain, while others remain on the sideline awaiting further data, especially with long-term results.
Problem 2: Is There a Role for Surgery to Specifically Treat T2DM?
Over many years, both medical and surgical specialists have observed that clinical and biochemical markers of T2DM improve after bariatric surgery.[41,46–51] Moreover, bariatric surgery is cost-effective over a lifetime in reducing mortality and diabetes complications in obese patients.[47,52,53] Also, there are fascinating direct and indirect effects of surgical perturbations on the enteroinsular axis with important downstream effects on incretins, glycemic control, appetite, and other metabolic pathways.[54–56] Nevertheless, some obese patients who have had bariatric surgery do not show improvement in their T2DM or experience a recurrence of T2DM after a presumed remission. This has been attributed to inadequate weight loss (the most important mechanism), disordered eating with overconsumption of energy-dense foods, severe insulin resistance and/or β-cell defect, misdiagnosis of latent autoimmune diabetes in adults, and/or surgical factors.
This information has fomented a paradigm shift in bariatric surgery from interventions primarily directed to obesity, to the broader category of metabolic disorders, namely T2DM. The Diabetes Surgery Summit was held in Rome, Italy, in 2007 at which time preliminary data were presented and sentiments regarding diabetes surgery were polled and reported. In 2008, the first World Congress for Interventional Therapies for Diabetes was convened in New York where controversies were systematically explored and further research was advocated. In 2011, the second World Congress for Interventional Therapies for Diabetes was held with an apparent consensus that, in fact, surgery may have a role in select patients with T2DM. The International Diabetes Federation articulated the role of bariatric surgical procedures for the management of T2DM in a position statement. In short, they stated that in response to a significant global problem, and based on the proven long-term safety and effectiveness of these procedures, bariatric surgery should be a treatment option for patients with T2DM and a BMI of 35 kg/m2 or greater without comorbidities, or a BMI of 30 kg/m2 or greater with comorbidities, in whom intensive lifestyle intervention and pharmacotherapy are unable to achieve treatment targets. This position has also been expressed in the recently published 2011 AACE CPG for a diabetes comprehensive care plan. In this document, recommendation R11 states that for patients with T2DM, LAGB may be considered in those with a BMI greater than 30 kg/m2 and Roux-en-Y gastric bypass (RGB) may be considered in those with a BMI greater than 35 kg/m2 to achieve at least short-term weight loss.
There are 2 broad categories of surgical interventions for T2DM: those that are already approved for use for obesity (purely restrictive: LAGB and laparoscopic sleeve gastrectomy [LSG]; combined restrictive and malabsorptive: laparoscopic gastric banding (LGB) and biliopancreatic diversion with duodenal switch [BPD-DS]) and those that are investigational and designed specifically for the management of T2DM (eg, ileal transposition  and duodeno-jejunal bypass [55,62]). How do we frame the problem regarding diabetes surgery? First, the timing of surgery must be based on clinical trials with intent-to-treat analyses for diabetes endpoints, demonstration of long-term safety and effectiveness, and appropriate comparator groups. Should the procedure be recommended early in the course of T2DM when patients are at low risk and prevention of complications is desired? Should the procedure be recommended late in the course of T2DM when CVD complications may not be preventable, as suggested by the recent ACCORD (Action to Control Cardiovascular Risk in Diabetes) and SCOUT (Sibutramine Cardiovascular Outcome Trial) trials? Or, should an intermediate timing be considered? Second, the selection of the optimal surgical procedure must still be formalized. For instance, even though gastric banding procedures may be safer, the glycemic control benefits are primarily related to weight loss. More aggressive procedures that bypass the proximal and/or distal intestine may create a favorable incretin milieu for longer-term benefits. Investigational procedures can be technologically less invasive and have antidiabetic effects without bariatric effects. Unfortunately, very few prospective studies have an intent-to-treat design for T2DM in which both control (nonsurgical therapy) and treatment (surgical therapy) patients are selected based on the presence of T2DM. Also, there are essentially no head-to-head studies comparing different bariatric surgery studies for the treatment of T2DM. Third, better follow-up strategies must be formulated with diabetes surgery. One of the major apprehensions for a broader indication for bariatric surgery is the appearance of nutritional and metabolic complications that overwhelm a medical system already suffering from a shortage of physician experts in nutritional medicine.
Problem 3: The Sleeve Gastrectomy
Sleeve gastrectomy is the restrictive component of the BPD-DS. The greater curvature of the stomach is resected, creating a narrow tubular passageway that results in a gastric volume of approximately 100 cc. In recent years, the LSG has been performed as a single definitive bariatric surgical procedure, part of an intended hybridized (with LGB or vertical banded gastroplasty) or staged (very high initial BMI; followed by LGB or BPD-DS) procedure, or as a revisional option after a failed bariatric procedure (LAGB, vertical band gastroplasty, or previous LSG).[65,66] The LSG also has significant antidiabetic benefits that are comparable to those of LGB.[67,68] Complications include stapler-line leakage, gastrointestinal reflux, intra-abdominal or intraluminal bleeding, trocar site hernia, pulmonary embolism, and strictures.[69,70] Although the procedure is safe and effective for weight loss, there can be weight regain after 5 years or insufficient weight loss due to neurohormonal factors or a physiologically dilated remnant stomach. A second staged bariatric procedure to incorporate a malabsorptive component, or a Silastic ring to prevent lower gastric sleeve dilatation, may be considered to assist with weight loss. The decision of whether to recommend LAGB, LGB, or LSG remains difficult without a clear evidence base to generically support one procedure over another. Ultimately, the choice is based in the context of specific metabolic goals, specific patient risk factors, and specific performance attributes of the surgeon and medical center. Shi et al still view the LSG procedure as investigational because of insufficient demonstration of a long-term beneficial operational impact in the management of obesity.
Problem 4: Nutritional and Metabolic Follow-up of the Patient Undergoing Bariatric Surgery
Perhaps the most relevant shortcoming for clinical endocrinologists in the care of patients undergoing bariatric surgery is the perioperative nutritional and metabolic management ( Table 3 ). Whether this has resulted from a critical shortage in physician nutrition experts and teachers and mentors in nutritional medicine, or from a culture where clinical endocrinologists are not routinely involved in the perioperative care of the bariatric surgery patient, more diligent monitoring of these nutritional and metabolic disorders in this patient population is desperately needed.
Preoperatively, it is vital to recognize that obese patients are not only at risk for nutritional deficiencies, but actually manifest them biochemically and/or clinically (eg, iron deficiency in 44% of patients, thiamine deficiency in 29%, and vitamin D deficiency in 68% ), and these nutrients should be replenished. Postoperatively, the distribution and severity of specific nutrient deficiencies depend on the bariatric procedure performed and the functional gastrointestinal anatomy disrupted. For example, restrictive procedures (such as LAGB and LSG) that affect gastric anatomy will also potentially compromise intrinsic factor production and bioavailability of iron, thus affecting vitamin B12 and iron status, respectively. Malabsorptive procedures that bypass portions of the proximal small intestine (such as RGB and BPD-DS) will affect absorption of water-soluble vitamins, such as folate, thiamine, and niacin.[75,76] More extensive bypass of the small intestine, as with distal RGB gastric bypass or BPD-DS, can result in clinically significant protein deficiency (7.7% to 11.9%, compared with less than 1% to 4.7% with gastric bypass) and fat malabsorption with the potential for deficiencies in essential fatty acids and the fat-soluble vitamins.[1,77]
In addition to the relatively straightforward problems of single-nutrient deficiencies are the more complex nutrient-metabolism interactions that produce postoperative complications. For instance, the metabolic bone disease observed in patients who have undergone bariatric surgery may be related to more than just vitamin D deficiency or negative calcium balance. There are complex physiological mechanisms related to changes in body composition, intestinal health, and the leptin-hypothalamic-osteoblast-enterocyte-pancreatic β-cell network. Moreover, patients who have undergone bariatric surgery and have dumping syndrome, nutritional anemia, neuropathy, or kidney stones may also find their way to an endocrinologist’s office.
The role of bariatric surgery is evolving and now takes the form ofmetabolic surgery, which targets specific elements: adiposity, T2DM, dyslipidemia, hypertension, and CVD. The role of the clinical endocrinologist is similarly evolving and must keep pace with technologic innovations and an expanding evidence base in obesity and T2DM management. The controversies discussed above emphasize the need for specialized care that can be provided by a clinical endocrinologist. What will the future hold?
Undoubtedly, clinical endocrinologists will need to hone their skills for collaboration in the care of the patient who is overweight or obese and has T2DM. This includes familiarization with the standard, as well as investigational, bariatric surgical procedures, particularly with respect to their long-term safety, efficacy and effectiveness, and mechanisms of action. A concerted effort by endocrine fellowship programs to provide dedicated training in the broad area of nutritional medicine should be advocated. There will be a continued emergence of white papers that, hopefully, will represent a collaborative spirit among professional societies and demonstrate areas of agreement while transparently describing areas of contention. These documents will serve to guide clinical decision-making, but will not supplant humanism that incorporates subjective and idiosyncratic factors for individual patients. Ultimately, bariatric surgical procedures are expected to be used more widely, finding their niche in CPG and algorithms for obesity and T2DM.