Roux-en-Y gastric bypass versus calorie restriction: support for surgery as the direct contributor to aloncltered responses of insulin and incretins to a mixed meal

Summary, in English

Abstract

Objective

To study the immediate effects of Roux-en-Y gastric bypass (RYGB) on glucose homeostasis, insulin, and incretin responses to mixed-meal tests compared with the effects of calorie restriction (CR).

Setting

University-affiliated bariatric surgery clinic.

Background

RYGB induces remission of type 2 diabetes (T2 D) long before significant weight loss occurs. The time course and underlying mechanisms of this remission remain enigmatic. A prevailing theory is that secretory patterns of incretin hormones are altered due to rearrangement of the gastrointestinal tract. To what extent reduced calorie intake contributes to the remission of T2 D is unknown.

Methods

Nine normoglycemic patients and 10 T2 D patients were subjected to mixed-meal tests (MMT) 4 weeks before surgery before initiation of a very low calorie diet regimen (MMT-4 w), 1 day before surgery on a very low calorie diet regimen (MMT-1 d), on the morning of the first day after surgery (MMT+1 d; first postsurgical meal), and 6 weeks after surgery (MMT+6 w). Insulin, glucose, active glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were measured.

Results

CR lowered insulin in T2 D patients, whereas glucose, GIP, and GLP-1 were unaffected. RYGB immediately increased plasma insulin and GIP. The GLP-1 response was delayed compared with the GIP response. T2 D patients exhibited lower insulin responses after RYGB compared with normoglycemic patients. GIP responses were similar in both groups at all occasions, whereas T2 D patients displayed markedly elevated GLP-1 responses 6 weeks after RYGB. Glucose was unaffected by CR and RYGB in both groups. Insulin sensitivity was unaffected by CR but improved with RYGB.

Conclusion

RYGB exerts powerful and immediate effects on insulin and incretin responses to food, independently of changes caused by CR.