Gastric bypass surgery has a weight-loss independent effect on post-challenge serum glucose levels

Gastric bypass surgery seems to have an effect on glucose metabolism beyond what is mediated through weight reduction. The magnitude of this effect on fasting and post-challenge glucose levels remains unknown.

Morbidly obese subjects without known diabetes performed a 75 g oral glucose tolerance test before and after either gastric bypass surgery (n = 64) or an intensive lifestyle intervention programme (n = 55), ClinicalTrials.gov identifier NCT00273104. The age-adjusted effects of the therapeutic procedures and percentage weight change on fasting and 2-h glucose levels at 1 year were explored using multiple linear regression analysis. Mean (SD) serum fasting and 2-h glucose levels at baseline did not differ between the surgery and lifestyle groups. Weight-loss after surgical treatment and lifestyle intervention was 30 (8) and 9 (10) % (p < 0.001). At 1 year, fasting and 2-h glucose levels were significantly lower in the surgery group than in the lifestyle group, 4.7 (0.4) versus 5.4 (0.7) mmol/l and 3.4 (0.8) versus 6.0 (2.4) mmol/l, respectively (both p < 0.001). Gastric bypass and weight-loss had both independent glucose-lowering effects on 2-h glucose levels [B (95 % CI) 1.4 (0.6-2.3) mmol/l and 0.4 (0.1-0.7) mmol/l per 10 % weight-loss, respectively]. Fasting glucose levels were determined by weight change [0.2 (0.1-0.3) mmol/l per 10 % weight-loss] and not by type of treatment.

Gastric bypass surgery has a clinically relevant glucose-lowering effect on post-challenge glucose levels which is seemingly not mediated through weight-loss alone.