Gastric bypass surgery changes food preferences so that they eat less high fat food

ScienceDaily (July 27, 2011) — 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."

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.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Imperial College London.

Journal Reference:

C. W. Le Roux, M. Bueter, N. Theis, M. Werling, H. Ashrafian, C. Lowenstein, T. Athanasiou, S. R. Bloom, A. C. Spector, T. Olbers, T. A. Lutz. Gastric bypass reduces fat intake and preference. AJP: Regulatory, Integrative and Comparative Physiology, 2011; DOI: 10.1152/ajpregu.00139.2011

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Adding a stent during minimally invasive surgery to repair aneurysms prevents recurrence, study suggests

ScienceDaily (July 26, 2011) — The addition of a simple stent can help prevent potentially lethal blood vessel bulges in the brain from recurring after they are repaired in a minimally invasive "coiling" procedure, according to new research by Johns Hopkins physicians. A report on the research, published in the July Journal of Neurointerventional Surgery, could make coiling a more viable option for the 30,000 people diagnosed with brain aneurysms each year in the United States, the investigators say.

Cerebral aneurysms, abnormal outward pouching of blood vessels in the brain, are traditionally repaired by an "open" operation, in which surgeons remove part of the skull, cut into the brain to reach the affected blood vessel, and then place a metal clip on the vessel where it balloons outward to close it down. In the past several years, surgeons are increasingly repairing aneurysms through coiling, in which they thread a platinum wire into a small incision in the groin, push it through the body's network of blood vessels to the bulging one, then pack the wire into the bulge where a natural clotting reaction closes it off.

Though endovascular (through the vessel) coiling has significant benefits compared to clipping, such as a lower risk of infection and recovery times measured in weeks instead of months, it also comes with a significant drawback -- recurrence of the aneurysm about a third of the time, says study leader Alex Coon, M.D., assistant professor of neurosurgery, neurology and radiology and director of endovascular surgery at the Johns Hopkins University School of Medicine. Traditional aneurysm surgery has a low recurrence rate of about two percent.

To avoid recurrence and the need for further surgery, some surgeons have experimented with insertion of a stent, or small tube, in the blood vessel near the neck of the aneurysm. The goal is to prop open the affected vessel so that more wire can be packed into the bulge.

To learn whether stents actually prevent recurrence or add complications, Coon and his colleagues looked at medical records of 90 people whose aneurysms were repaired by coiling at The Johns Hopkins Hospital between May 1992 and March 2009. A stent was used in a third of the operations.

After two years of follow-up, the researchers found that aneurysms recurred in more than 40 percent of patients who did not have stents. The recurrence rate in the stented patients was only about 15 percent, and stented patients had no more complications than those without stents.

Coon notes that endovascular surgery for aneurysms is becoming more common, and knowing what can prevent recurrence will help surgeons and patients make informed decisions about the choice of procedure.

"It's easy to treat someone's aneurysm, but can you treat it durably and make it last? We've now shown in our study that stenting -- something that makes sense from an engineering perspective, a clinical perspective and a common sense perspective -- truly works," he says.

Other Johns Hopkins researchers who participated in this study include Geoffrey P. Colby, Alexandra R. Paul, Martin G. Radvany, Dheeraj Ghandi, Philippe Gailloud, Judy Huang, and Rafael J. Tamargo.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Johns Hopkins Medical Institutions, via EurekAlert!, a service of AAAS.

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