Now, gastric bypass surgery to shed weight

Gastric bypass surgery alters people's food preferences so that they eat less high fat food, according to a new study led by scientists at Imperial College London. The findings, published in the American Journal of Physiology - Regulatory, Integrative, and Comparative Physiology, suggest a new mechanism by which some types of bariatric surgery lead to long-term weight loss.

A growing number of obese patients are choosing to undergo bariatric surgery in order to lose weight, with over 7,000 such procedures being carried out on the NHS in 2009-10. The most common and the most effective procedure is the 'Roux-en-Y' gastric bypass, which involves stapling the stomach to create a small pouch at the top, which is then connected directly to the small intestine, bypassing most of the stomach and the duodenum (the first part of the small intestine). This means that patients feel full sooner.

The new study involved data from human trials as well as experiments using rats. The researchers used data from 16 participants in a study in which obese people were randomly assigned either gastric bypass surgery or another type of operation, vertical-banded gastroplasty, in which the stomach volume is reduced but no part of the intestine is bypassed. The participants who had had gastric bypass had a significantly smaller proportion of fat in their diet six years after surgery, based on questionnaire responses.

In the rat experiments, rats given gastric bypass surgery were compared with rats that were given a sham operation. Rats that had gastric bypass surgery ate less food in total, but they specifically ate less high fat food and more low fat food. When given a choice between two bottles with different concentrations of fat emulsions, the rats that had gastric bypass surgery showed a lower preference for high fat concentrations compared with rats that had a sham operation.

"It seems that people who've undergone gastric bypass surgery are eating the right food without even trying," said Mr Torsten Olbers from Imperial College London, who performed the operations on patients in the study at Sahlgrenska University Hospital in Göteborg, Sweden.

Dr Carel le Roux, from the Imperial Weight Centre at Imperial College London, who led the research, said: "It appears that after bypass surgery, patients become hungry for good food and avoid junk food not because they have to, but because they just don't like it any more. If we can find out why this happens, we might be able to help people to eat more healthily without much effort."