Obesity




Study shows gastric bypass makes people prefer low-fat food

 

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. The British NHS carried out over 7,000 such procedures 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. This means that patients feel full sooner.

In the new study researchers used data from 16 obese participants who were randomly assigned either gastric bypass surgery or 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.

Also data from rat experiments showed that 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 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.”

The rat experiments suggested that the reduced preference for high fat food was partly due to the effects of digesting the food. There was no difference in preferences between gastric bypass rats and sham-operated rats when the rats were only given access to the bottles for a few seconds, suggesting that bypass rats did not dislike the taste of high fat emulsions when they were only allowed small volumes at a time.

Rats can learn to avoid foods that they associate with illness, so the researchers tested whether high fat foods would condition them to avoid certain tastes. They gave the rats saccharine-flavoured water while infusing corn oil into their stomachs. The gastric bypass rats learned to avoid saccharine, but the sham-operated rats did not, suggesting that the effect of digesting corn oil was unpleasant to the rats that had had gastric bypass surgery.

Levels of the satiety-promoting hormones GLP-1 and PYY were higher after feeding in the gastric bypass rats compared with sham-operated rats, suggesting a possible mechanism for the changes in food preferences. The team at Imperial plan to study the role of these hormones further to see if it might be possible to mimic the effects of gastric bypass without using surgery. doi: 10. 1152/ ajpregu. 00139. 2011
 

Obesity is a global problem

The worldwide prevalence of obesity has nearly doubled since 1980, according to a major study on how three important heart disease risk factors have changed across the world over the last three decades. The study, published 4 February 2011 in three papers in the Lancet, looked at all available global data to assess how body mass index (BMI), blood pressure and cholesterol changed between 1980 and 2008.

The study shows that in 2008, more than one in 10 of the world’s adult population was obese, with women more likely to be obese than men. An estimated 205 million men and 297 million adult women were obese – a total of more than half a billion adults worldwide.

Professor Majid Ezzati, the senior author of the study from the School of Public Health at Imperial College London, said: “Our results show that overweight and obesity, high blood pressure and high cholesterol are no longer Western problems or problems of wealthy nations. Their presence has shifted towards low and middle income countries, making them global problems.
 


 D
ate of upload: 18th Oct 2011

 

                                  
                                               Copyright © 2011 MiddleEastHealthMag.com. All Rights Reserved.