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Insulin outcomes

Study: weight loss causes improved insulin resistance

A close up of pancreatic cells. A new study suggests that substantial weight loss improves beta cell function post-surgery. Photo: Flickr / aneps omar
Metabolic response to gastric bypass and gastric band surgery similar at comparable levels of weight loss
Findings lead researchers to conclude that improved insulin sensitivity and beta cell function a result of substantial weight loss, not altered anatomy

Dramatic weight loss, and not adjusted anatomy, is the cause of improved insulin sensitivity in bariatric surgery patients, according to a study published in the Journal of Clinical Investigation.

Investigators found that patients who had lost 20% of their body weight after surgery had a similar improvement in insulin resistance and beta cell function, regardless of whether they had adjustable gastric band surgery or Roux-en-Y gastric bypass.

The finding led the researchers to conclude that the improved diabetes resolution commonly experienced after gastric bypass is likely to be due to the fact that it normally results in superior weight loss, rather than it being a side effect of the diversion of the upper gastrointestinal tract, as is commonly thought.

The investigators compared ten patients who had undergone gastric band surgery with ten patients who had undergone Roux-en-Y gastric bypass. Outcomes were measured in the gastric band group when they had lost an average of 19.3% ± 1.9% of their body weight, at 22 ± 7 weeks after surgery, and in the gastric bypass group when they had lost 20.1% ± 2.3% of their body weight, at 16 ± 2 weeks after surgery.

At this point, both groups were found to have halved their resistance to insulin, as measured by the homeostasis model assessment of insulin resistance, and there was no significant difference between groups. Insulin-mediated stimulation of glucose disposal above basal values nearly doubled after weight loss in both groups, but there was no significant difference between groups.

Similarly, the total beta cell sensitivity decreased after surgery to the same extent in both groups. The patients’ disposition index nearly doubled in both groups, again to a similar extent.

However, the Roux-en-Y group showed a much faster delivery of ingested glucose into the circulation, leading to an early increase in plasma glucose concentration and insulin secretion.

For the study, the researchers chose patients who demonstrated insulin resistance, but did not have type 2 diabetes, saying that it allowed them to avoid potential confounding effects, including differences in baseline glycemic control, glucose toxicity, and changes in diabetes medications.

They note that this means the findings of their study cannot be generalised to the diabetic population, and that further study is needed to establish whether the effects found can be replicated in patients with type 2 diabetes.

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