July 28, 2011
Food Preferences Change After Gastric Bypass Surgery
Gastric bypass surgery, once a procedure of last resort for obese patients is quickly becoming an accepted and mainstream procedure used by patients to eat less, lose weight and become healthier. However, the actual reasons behind this surgery's success have been unclear.
The most common and effective procedure is the "ËRoux-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. This bypasses most of the stomach and the duodenum (the first part of the small intestine), and appears to lead patients to significantly reduce their intake of dietary fat.
A new study, published in the American Journal of Physiology, suggests a new reason why some types of bariatric surgery lead to long-term weight loss more successfully than others.
Further experiments suggest that this fat avoidance is triggered through digestive consequences, rather than just altered taste, and may be the result of an excess of hormones previously linked to food avoidance.
Researchers used data from a study in obese people comparing gastric bypass to vertical-banded gastroplasty. At 1 and 6 years after surgery, these patients were asked to fill out questionnaires to determine whether they avoided certain foods.
The researchers also performed either Roux-en-Y gastric bypass or sham operations on rats. At time points ranging from 10 to 200 days after surgery, these animals were subjected to various food preference experiments. In one experiment, the rats were offered either high- or low-fat chow, with the researchers comparing the animals' intake of both foods before and after surgery.
Similarly, the rats were presented with bottles containing either water or various concentrations of a fat emulsions, with the researchers recording intake of each liquid. To determine whether taste could be responsible for preference, the researchers recorded how many licks the animals took at each bottle when it was offered for only a brief amount of time.
The results suggest that people and animals who undergo Roux-en-Y gastric bypass decrease their consumption of both solid and liquid dietary fat, possibly helping people stick to a healthier diet.
This avoidance does not appear to be triggered by taste alone, but can be influenced by the effects after ingestion. The hormone GLP-1 might be partly responsible for these effects.
"These findings suggest that changes in fat preference may contribute to long-term maintained weight loss after gastric bypass," the authors wrote. "By elucidating the mechanisms by which obesity surgery reduces the consumption of high fat foods, new surgical and non-surgical therapies could be developed that mimic these mechanisms to offer safe and effective weight loss."
"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."
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