Gastric Bypass and Banding Both Improve Metabolic Response

Yael Waknine

December 04, 2012

Weight loss from bariatric surgery, not the type of procedure used, appears responsible for improvement of metabolic responses in obese, insulin resistant, nondiabetic patients, according to results from a study published online November 26 and in the December issue of the Journal of Clinical Investigation.

Researchers led by Samuel Klein, MD, from the Center for Human Nutrition, the Washington University School of Medicine in St. Louis, Missouri, compared the metabolic effects of 20% weight loss induced by either laparoscopic adjustable gastric banding (LAGB) or Roux-en-Y gastric bypass (RYGB) surgery in nondiabetic, insulin-resistant obese adults.

They found that both procedures equally improved insulin sensitivity and β-cell function and concluded that the advantages were derived from the amount of weight lost (LAGB, 19.3% ± 1.9% and RYGB, 20.1% ± 2.3%, respectively).

Insulin sensitivity, as assessed using the homeostasis model assessment of insulin resistance score, decreased by more than 50%, with no significant difference between the LAGB and RYGB groups, which went from 5.8 ± 1.9 to 2.3 ± 0.8 and 5.8 ± 2.3 to 1.8 ± 0.9, respectively (P < .05 for each reduction).

With respect to β-cell function, similar decreases in total insulin secretion rate response to a mixed meal were observed after both LAGB and RYGB surgery-induced weight loss. "Static [insulin secretion rate] decreased to a similar extent after both LAGB (from 41.3 ± 4.6 × 103 to 31.5 ± 5.1 × 103 nmol/l per 360 min) and RYGB (from 45.1 ± 13.4 × 103 to 29.2 ± 5.0 ×103 nmol/l per 360 min) surgery-induced weight loss," the authors write. Total β cell sensitivity decreased after surgery-induced weight loss to the same extent in both groups, as evidenced by a near doubling of the disposition index.

The only difference was in metabolic response patterns to a mixed meal. RYBG surgery was associated with rapid delivery of ingested glucose into the systemic circulation, leading to a large early insulin response. No such spikes in glucose and insulin levels were observed among patients in the LAGB group.

Challenges Current Assumptions

"This is a tremendous achievement that carefully documents the early response to glucose metabolism after weight-loss surgery," Edward Lin, DO, MBA, director of the endosurgery unit and gastroesophageal Treatment Center and surgical director of bariatrics at Emory University School of Medicine in Atlanta, Georgia, told Medscape Medical News in an interview.

"It is well-known that weight loss is a strong predictor of insulin sensitivity. But frankly, I am surprised that simple weight loss without much physiologic alteration of the gastrointestinal tract improves insulin secretion. If the authors are correct, it would challenge present assumptions that it is the diversion of nutrient flow that augments insulin secretion," Dr. Lin said, noting that the insulin surge in patients in the RYGB group underscores an element of physiologic change that has not been fully explained.

"Moreover, if the authors are correct, it would also mean that simple weight loss from diet restriction will improve diabetes, which is well-known. However, it can also mean that patients do not need an invasive procedure such as RYGB to improve glucose metabolism," Dr. Lin added, noting that the metabolic surgery community observes just the opposite clinically: RYGB is more effective in improving type 2 diabetes long-term. According to Dr. Lin, LAGB is prone to complications in the global surgical community, and up to 50% of bands are removed within 10 years.

The study was supported by grants from the National Institutes of Health, Ethicon Endo-Surgery, and the Atkins Foundation Philanthropic Trust. Dr. Klein serves on a Scientific Advisory Board for Ethicon Endo-Surgery. Dr. Lin has disclosed no relevant financial relationships.

J Clin Invest. 2012;122:4667-4674. Full text