Gastric bypass Surgery has glucose-lowering effect independent of weight loss

Although gastric bypass is known to result in a reduction in glucose levels, a study by researchers from Norway and Denmark has found that is it independent of weight-loss. According to the study authors from the Vestfold Hospital Trust, Tønsberg, Oslo University Hospital, Oslo, Norway, and the Endocrinology Research Section, Copenhagen, Denmark, the paper, ‘Gastric bypass surgery has a weight-loss independent effect on post-challenge serum glucose levels’, published in journal, Diabetology & Metabolic Syndrome, is further evidence that the procedure has specific glucose regulatory mechanisms.

The investigators wanted to assess the effects of weight-loss achieved by gastric bypass surgery and lifestyle intervention on one year fasting and 2h glucose levels. Data from oral glucose tolerance tests (OGTTs) in the previously published ‘Morbid Obesity treatment, Bariatric surgery versus Intensive Lifestyle intervention’ (MOBIL) study were analysed and they included from a non-surgical weight-loss group allowing them to assess the specific effect of the surgical procedure on fasting and post-challenge glucose levels.

The trial included 146 morbidly obese subjects of mainly European descent, and aimed to address changes in several health outcomes related to obesity after gastric bypass surgery or an intensive lifestyle intervention programme. A 75g 2 hour OGTT was performed in subjects without known diabetes (119 out of 139 completers) at the time of inclusion.

Patients in the surgery group received laparoscopic Roux-en-Y gastric bypass, whereas patients who chose lifestyle intervention were referred to a rehabilitation centre specialising in the care of morbidly obese patients. The one year lifestyle programme at the rehabilitation centre aimed to induce a weight-loss of at least 10% and comprised of four stays at the centre lasting for either one or four weeks (total weeks week stay).


Patients in the surgery group were younger [41 (10) versus 46 (11) years,  =0.007], heavier [47 (6) versus 43 (5) kg/m 2 , p<0.001] and had greater weight-loss at one-year follow-up [30 (8) versus 9 (10) %, p<0.001]. The proportion of females did not differ between the surgery and lifestyle groups (70 versus 71 %, p=0.943). Fasting and 2 hour glucose levels at baseline did not differ between the surgery and lifestyle groups, 6.1 (1.6) versus 6.0 (1.0) mmol/l, p = 0.495 and 7.5 (3.4) versus 7.6 (3.1) mmol/l, p=0.887. In contrast, both fasting and 2 hour glucose levels were significantly lower in the surgery group than in the lifestyle group at one year, 4.7 (0.4) versus 5.4 (0.7) mmol/l and 3.4 (0.8) versus 6.0 (2.4) mmol/l (both p<0.001).

The correlations between percentage weight change and fasting and 2 hour glucose levels one year after surgical and medical treatment are shown in Figure 1. Weight change correlated significantly with fasting glucose levels at one year in both groups.

Glucose post-bypass figure 1

Correlations between percentage weight change and fasting and 2-h glucose levels at 1 year in the surgery and lifestyle groups. **p < 0.01, *p < 0.05

The associations between weight change and fasting and 2 hour glucose levels in the two groups did not differ significantly (no “group × weight change” interactions, p=0.371 and p=0.130, respectively). Age was positively associated with both fasting glucose levels and 2 hour glucose levels and explained 18 and 13 % of the variance in the respective glucose variables. Overall, treatment choice, weight change and age explained 46 % (R 2  = 0.459) and 49 % (R 2  = 0.491) of the variance in fasting and 2 hour glucose levels one year after treatment.

“The main finding of the present study is that gastric bypass surgery seems to have an effect on post-challenge glucose levels that is partly independent of weight loss, while the effect on fasting glucose levels is solely dependent on the degree of weight loss,” the researchers note. “These results support the idea that gastric bypass surgery has a direct effect on glucose metabolism beyond what is mediated by weight change. However, the effect seems to be specific for the post-prandial phase.”

They also state that weight-loss independent glucose lowering effect of gastric bypass surgery on 2 hour glucose levels might be beneficial in subjects with post-prandial hyperglycaemia. These findings may suggest that younger subjects who experience large weight reduction after surgery may have an increased risk of developing post-prandial hypoglycaemia.

“The strong post-challenge glucose lowering effect of gastric bypass surgery on two hour glucose is partly independent of weight-loss,” the researchers conclude. “This finding supports the presence of gastric bypass specific glucose regulatory mechanisms.”



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