Gastric Bypass Improves Insulin Resistance

A new study has found that gastric bypass surgery appears to reset basal insulin levels; peak levels, however, remain unchanged.

Researchers at East Carolina University (Greenville, NC, USA) conducted a study involving 16 white women, aged 18 -60 years, with a body mass index (BMI) of 35-65; control subjects were lean euglycemic white women with a BMI below 25, who were not pregnant, did not smoke, and who exercised less than 1 hour 3 times per week. Prior to, and at one week and 3 months after surgery, the investigators drew fasting blood samples and then administered a 150 kcal mixed-meal challenge to morbidly obese nondiabetic subjects with a BMI above 35 (obese group), morbidly obese diabetic subjects (diabetic group), and to the lean control subjects (control group). Subsequently, intravenous glucose tolerance tests and blood samples were analyzed every three hours for glucose, insulin, C-peptide, and incretins, among other substances.

Using the homeostatic model assessment (HOMA) as a measure of insulin resistance, the investigators showed that insulin resistance decreased following surgery. At 3 months postsurgery, the diabetic group's HOMA was completely restored to the normal of the lean control group; the nondiabetic obese patients had HOMA scores of about 3 before surgery and of about 1 at 3 months after surgery; and the diabetic obese patient, who started with HOMA scores of about 10, went down to about 1.5 after surgery, which was within the range of the control subjects. The researchers also investigated acute insulin response to glucose (AIRg), which was lower in the diabetic than in the obese group before surgery, and found that the AIRg was higher in the obese than in the control group; At 3 months postsurgery, however, both groups had AIRg values close to those in the control group. The study was presented at the American College of Surgeons (ACS) annual clinical congress, held during October 2010 in Washington D.C. (USA).

"Although our obese and diabetic peak levels did not change, baseline insulin levels decreased, which has allowed for a more perfect response to the glucose challenge after gastric bypass surgery,” said study presenter and lead author John Pender, M.D. "These findings suggest that insulin sensitivity in the liver rather than in the muscle may play an important role in determining basal insulin levels.”

The researchers summarized the study results, explaining that gastric bypass surgery resets basal insulin levels, but peak insulin levels remain unchanged; therefore, the reversal of type 2 diabetes mellitus (T2DM) was not associated with an improvement in the ability to produce insulin, but was associated instead with an ability to control basal insulin levels and an appropriate response to meals. As result, insulin resistance, as measured by HOMA, returned to normal, but insulin sensitivity only partially normalized.

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East Carolina University