Roux-en-Y gastric bypass (RYGB) surgery effectively prevents or treats type 2 diabetes (T2D). Adipose tissue (AT) mechanisms may be of importance.

To assess the relationship between early changes in whole-body and AT metabolism in surgically treated patients with T2D.

A randomized single-center study.

Nineteen patients with T2D with body mass index 30 to 45 kg/m².

Thirteen patients were assessed at baseline and 4 and 24 weeks after RYGB (preceded by a 4-week low-calorie diet) and compared with 6 control patients continuing standard medical treatment: oral glucose tolerance test, subcutaneous AT biopsies for gene expression, adipocyte size, glucose uptake, lipolysis, and insulin action.

At 4 and 24 weeks post-RYGB, all patients but one had stopped diabetes medication. Fasting glucose, HbA_1c, and insulin levels decreased and the Matsuda index increased compared with baseline (P < 0.01 for all), indicating improved whole-body insulin sensitivity. Mean adipocyte size significantly reduced, more at 4 than at 24 weeks; at 4 weeks, glucose uptake per adipocyte was lowered, and isoproterenol-stimulated lipolysis tended to increase, whereas the fold insulin effects on glucose uptake and lipolysis were unchanged. Expression of genes involved in fatty acid oxidation, CPT1b and adiponectin, was increased at 4 weeks, whereas leptin and E2F1 (involved in cell proliferation) were reduced (P < 0.05 for all).

Glycemic control and in vivo insulin sensitivity improved 4 weeks after RYGB, but adipocyte insulin sensitivity did not change despite a marked reduction in adipocyte size. Thus, mechanisms for a rapid improvement of T2D after RYGB may occur mainly in other tissues than adipose.