Weight loss surgery could reverse diabetes

More than 20 million Americans suffer from type II diabetes and the incidence of this disease is on the rise. In diabetes, the body doesn't respond to the hormone insulin or process blood sugars effectively. Insulin is secreted from the pancreas and stimulates the cells of the body to take up sugars and generate energy.  In patients with type II diabetes, the cells become resistant to insulin and do not take up sugars in response, resulting in an increase in blood sugar levels. Elevated blood sugars cause vascular damage in different organs including the heart, kidneys, and nervous system. With the emergence of type II diabetes as a major public heath and medical problem, there are a multitude of treatments available, which help control blood sugars and reduce the complications of diabetes. It has been shown that weight loss can reduce insulin resistance through mechanisms that are not entirely understood. Diabetic patients are frequently advised to exercise and lose weight in order to reduce their blood sugars. 

Surgical interventions for weight loss are common and new studies are providing evidence that they may be beneficial for patients with diabetes. Surgical interventions for weight loss are collectively referred to as bariatric surgery. Three popular bariatric surgical procedures are Roux-en-Y gastric bypass (RYGB), sleeve gastrectomy, and biliopancreatic diversion. In RYGB surgery and biliopancreatic diversion, the stomach is made smaller and its connection to the intestine is changed in such a way to reduce absorption of food molecules. In sleeve gastrectomy the stomach is reduced to 25 percent of its original size, but attachments to the intestines are not altered and there is no change in absorption. 

This week, two clinical trials published in the New England Journal of Medicine demonstrated that bariatric surgery reduces blood sugars in patients with type II diabetes and may result in remission of the disease in a subgroup of patients. The first study was conducted at the Cleveland Clinic and compared diabetic patients receiving either RYGB or sleeve gastrectomy along with medical therapy to patients receiving medical therapy alone. In this study of 150 patients, those who underwent surgery in conjunction with medical therapy had a greater likelihood of reaching normal glycated hemoglobin levels (glycated hemoglobin is a measure of average blood sugar levels over the course of the previous three months) 1 year after surgery, than those patients who only received medical therapy. In the second study, conducted at Catholic University in Rome, 60 patients were randomly selected to receive medical therapy alone, medical therapy with RYGB surgery, or medical therapy with biliopancreatic diversion.  In this study, 75 percent and 95 percent of patients undergoing RYGB and biliopancreatic diversion respectively, had disease remission 2 years after surgery, but none of the patients undergoing medical therapy alone had remission. Also, patients who underwent surgery had greater improvements in their glycated hemoglobin levels.  In addition to the noted benefits in blood sugar levels, patients undergoing surgery also showed improvements in blood pressure and cholesterol levels.    

The findings of these studies are significant because they were conducted in a controlled fashion as randomized clinical trials. Prior to these studies, data demonstrating a relationship between bariatric surgery and blood sugar control were limited. These studies provide stronger evidence that bariatric surgery may indeed be an effective treatment approach for diabetic patients with obesity. Based on these results, providers may begin to recommend bariatric surgery more frequently in obese diabetic patients or those at risk for diabetes.  

The exact mechanisms through which bariatric surgery improves the body’s ability to process blood glucose are not understood. It is well known that weight loss increases the sensitivity of different tissues to insulin and reduces insulin resistance. However, experts believe additional mechanisms are at play. Some studies have found a link between branch-chained amino acid levels in the blood and insulin resistance such that patients with higher levels of branch-chained amino acids are at greater risk of developing diabetes years later. Research has shown that bariatric surgery may reduce the levels of branch-chained amino acids in the blood and thereby decrease insulin resistance. Scientists also believe gastric bypass surgery increases the levels of satiety hormones more effectively than weight loss. Increases in satiety hormones will reduce an individual’s desire to eat and help control blood sugars. Changes in the levels of incretins following bariatric surgery are also thought to play a role in blood sugar control.  Incretins are a group of hormones secreted from the intestines that stimulate insulin production from the pancreas and increase the uptake of blood sugars. Previous studies have found that gastric bypass surgery causes an increase in blood incretin levels. Nonetheless, how bariatric surgery affects incretin levels remains unclear. 

The findings from the two recently published studies are interesting and promising. However, experts recognize that it is too early to make large-scale conclusions. The two studies were single center studies with small sample sizes. Therefore, how well these results could be applied to the greater population remains unknown.  Furthermore, the follow up time in these studies did not exceed two years. Given the potential for relapse of obesity after bariatric surgery in some patients, it is important for future studies to follow up patients in the longer term to determine how long the improvements in blood sugar levels last.