By Monica Smith

Despite its reputation as the gold standard for weight loss, gastric bypass surgery may result in a post-meal glucose spike followed by a blood sugar crash that causes between-meal hunger, according to a new study. The research examined the effects of different bariatric procedures on post-meal glucose reactions.

Mitchell S. Roslin, MD, FACS, Lenox Hill Hospital, New York City, and his colleagues first became interested in glucose tolerance testing after noticing that many of their patients who regained weight after gastric bypass surgery complained of inter-meal hunger, especially following meals rich in simple carbohydrates.

“Consistent with that is the fact that there are new conditions—nesidioblastosis, noninsulinoma pancreatogenous hypoglycemia syndrome, hyperinsulinemia and hypoglycemia—[that are] becoming more common after gastric bypass,” Dr. Roslin said. “These are entities surgeons rarely encountered previous to this [era in bariatric surgery].” The research was presented at the 2013 meeting of the Society of American Gastrointestinal and Endoscopic Surgeons; the study was sponsored by Covidien.

Dr. Roslin and his team decided to compare glucose metabolism among patients who had undergone gastric bypass, sleeve gastrectomy or duodenal switch (DS), in which a common channel of at least 125 cm was preserved. “This type of model gives us the ability to compare two operations that preserve the pyloric valve, as well as two operations that have an intestinal bypass component,” he said.

In the prospective, nonrandomized study, 13 patients received gastric bypass, 12 received sleeve gastrectomy, and 13 underwent DS. All completed an oral glucose tolerance test (GTT) at baseline and six, nine and 12 months. The nine-month GTT comprised a solid mixed-meal muffin. The only significant, preoperative difference among the patients was greater body mass index in the DS group. There were no significant differences in their glucose homeostasis parameters, fasting glucose or insulin.

At 12 months, the DS patients lost significantly more weight than the other two groups, although those also experienced good weight loss. All of the operations reduced fasting blood glucose levels as well. But after GTT, the gastric bypass group had much higher levels of one-hour glucose than the DS group, and the sleeve gastrectomy group had intermediate levels. The gastric bypass group also had higher one-hour insulin levels, higher even than their preoperative level, whereas insulin was suppressed in the DS group.

“When you have high insulin, glucose falls, and we know that hypoglycemia causes hunger,” Dr. Roslin said. “Looking at the one- to two-hour glucose ratio, the gastric bypass patients have the highest one-hour sugar [levels] and the lowest two-hour sugar [levels], and I think this begins to explain why we have inter-meal hunger with gastric bypass.”

All of the operations resulted in significant weight loss and other positive outcomes, but compared with gastric bypass patients, DS patients had a much smaller rise in one-hour glucose and insulin levels. “The sleeve behaves intermediately to the bypass and DS, meaning that preserving the pylorus may be part of the explanation, but not the whole story,” Dr. Roslin said.

“Obviously, controlled trials between gastric bypass and DS are needed to determine the real long-term significance, but I think we should all be cautious before we label gastric bypass the gold standard operation,” he said.

Kevin M. Reavis, MD, FACS, esophageal and foregut surgery, Division of Gastrointestinal and Minimally Invasive Surgery, The Oregon Clinic, Portland, said that improved assays are allowing for a more rapid and better understanding of the true complexity of the physiologic changes that contribute to the results seen with each of the bariatric procedures. “This study highlights aspects of glucose metabolism that have previously been underappreciated.”

“Although it is a relatively small study, it illustrates that with gastric bypass, sleeve gastrectomy and duodenal switch, there are substantial metabolic changes we are just beginning to understand and must investigate on a larger scale in order to optimize clinical outcomes,” Dr. Reavis said.