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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Vascular changes linked to dementia, experts say

ScienceDaily (July 22, 2011) — The same artery-clogging process (atherosclerosis) that causes heart disease can also result in age-related vascular cognitive impairments (VCI), according to a new American Heart Association/American Stroke Association scientific statement published online in Stroke: Journal of the American Heart Association.

Cognitive impairment, also known as dementia, includes difficulty with thinking, reasoning and memory, and can be caused by vascular disease, Alzheimer's disease, a combination of both and other causes.

Atherosclerosis is a build- up of plaque in the arteries associated with elevated blood pressure, cholesterol, smoking and other risk factors. When it restricts or blocks blood flow to the brain, it is called cerebrovascular disease, which can result in vascular cognitive impairment.

Alzheimer's disease is a progressive brain disorder that damages and destroys brain cells. "We have learned that cerebrovascular disease and Alzheimer's disease may work together to cause cognitive impairment and the mixed disorder may be the most common type of dementia in older persons," said Philip B. Gorelick, M.D., M.P.H., co-chair of the writing group for the statement and director of the Center for Stroke Research at the University of Illinois College of Medicine at Chicago.

The prevalence of dementia increases with advancing age and affects about 30 percent of people over 80 years of age, costing more than $40,000 per patient annually in the United States, according to the statement authors. . .

Treating risk factors for heart disease and stroke with lifestyle changes and medical management may prevent or slow the development of dementia in some people, Gorelick said. Physical activity, healthy diet, healthy body weight, tobacco avoidance as well as blood pressure and cholesterol management could significantly help many people maintain their mental abilities as they age.

"Generally speaking, what is good for the heart is good for the brain," Gorelick said. "Although it is not definitely proven yet, treatment or prevention of major risk factors for stroke and heart disease may prove to also preserve cognitive function with age."

Understanding common causes of late-life cognitive impairment and dementia has advanced and many of the traditional risk factors for stroke also are risk markers for Alzheimer's disease and vascular cognitive impairment. For example:

• Reducing high blood pressure is recommended to reduce the risk of vascular cognitive impairment. High blood pressure in mid-life may be an important risk factor for cognitive decline later in life. • Controlling high cholesterol and abnormal blood sugar may also help reduce the risk of vascular cognitive impairment, although more study is needed to confirm the role of these interventions. • Smoking cessation could lessen the risk of vascular cognitive impairment. • Increasing physical exercise, consuming a moderate level of alcohol (i.e., up to 2 drinks for men and 1 drink for non-pregnant women) for those who currently consume alcohol; and maintaining a healthy weight may also lessen the risk of VCI, but more study is needed to confirm usefulness. • Taking B vitamins or anti-oxidant supplements, however, does not prevent vascular cognitive impairment, heart disease or stroke.

Identifying people at risk for cognitive impairment is a promising strategy for preventing or postponing dementia and for public health cost savings, the writers said. "We encourage clinicians to use screening tools to detect cognitive impairment in their older patients and continue to treat vascular risks according to nationally- or regionally-accepted guidelines." Vascular cognitive impairment is most obvious after a stroke, but there could be cognitive repercussions from small strokes, microbleeds or areas of diminished blood flow in the brain that cause no obvious neurological symptoms, according to the statement.

In many cases, the risk factors for vascular cognitive impairment are the same as for stroke, including high blood pressure, high cholesterol, abnormalities in heart rhythm and diabetes. The American Academy of Neurology and the Alzheimer's Association have endorsed the statement.

Other members of the writing group include: Angelo Scuteri, co-chair, M.D., Ph.D.; David Bennett, M.D.; Sandra E. Black, M.D.; Charles DeCarli, M.D.; Helena C. Chui, M.D.; Steven M. Greenberg, M.D., Ph.D.; Randall T. Higashida, M.D.; Costantino Iadecola, M.D.; Lenore J. Launer, M.D.; Stephane Laurent, M.D.; Oscar L. Lopez, M.D.; David Nyenhuis, Ph.D.; Ronald C. Petersen, M.D., Ph.D.; Julie A. Schneider, M.D.; Christophe Tzourio, M.D., Ph.D.; Donna K. Arnett, Ph.D.; Ruth Lindquist, Ph.D., R.N.; Peter M. Nilsson, M.D., Ph.D.; Gustavo C. Roman, M.D.; Frank W. Sellke, M.D.; and Sudha Seshadri, M.D. Author disclosures are on the manuscript.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Heart Association.

Journal Reference:

Philip B. Gorelick, Angelo Scuteri, Sandra E. Black, Charles Decarli, Steven M. Greenberg, Costantino Iadecola, Lenore J. Launer, Stephane Laurent, Oscar L. Lopez, David Nyenhuis, Ronald C. Petersen, Julie A. Schneider, Christophe Tzourio, Donna K. Arnett, David A. Bennett, Helena C. Chui, Randall T. Higashida, Ruth Lindquist, Peter M. Nilsson, Gustavo C. Roman, Frank W. Sellke, and Sudha Seshadri, on behalf of the American Heart Association Stroke Council, Council on Epidemiology and Prevention, Council on Cardiovascular Nursing, Council on Cardiovascular Radiology and Intervention, and Council on Cardiovascular Surgery and Anesthesia. Vascular Contributions to Cognitive Impairment and Dementia: A Statement for Healthcare Professionals From the American Heart Association/American Stroke Association. Stroke, 2011; DOI: 10.1161/STR.0b013e3182299496

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Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

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