SCI-TECH & AGRI

Key to weight loss found

Gastric bypass surgery can achieve long-term weight loss while dieting, exercise and medications fail.

Gastric bypass surgery can achieve long-term weight loss while dieting, exercise and medications fail.  

THOUSANDS OF obese people know firsthand that gastric bypass surgery can achieve long-term weight loss when dieting, exercise and medications have failed.

The reason for the difference may hinge on a recently discovered appetite-stimulating hormone, according to an article in the New England Journal of Medicine.

A study led by a team at the Veterans Affairs (VA) Puget Sound Health Care System and the University of Washington (UW) compared the blood samples from the dieters and gastric-bypass patients and found dramatic differences in the levels of `ghrelin,' a hormone secreted by the stomach.

The hormone was first identified by Japanese researchers in 1999, and was shown by British scientists last year to trigger appetite in humans.

The study shows that dieting raises ghrelin, while gastric bypass surgery reduces it to undetectable levels.

According to lead author David E. Cummings, the findings shed light on what may be an underlying reason for the success of gastric bypass surgery.

It also raises the possibility of a new generation of safer, effective weight-loss drugs.

Currently available weight-loss drugs work mainly by raising levels of the neurotransmitters serotonin and norepinepherine, which can increase metabolism and reduce appetite; or by blocking the absorption of fat in the digestive tract.

But many of these medications have potentially serious side effects, such as hypertension.

Gastric bypass surgery works because 95 per cent of the stomach is sewn shut so it can't receive food. As a result, the patient feels full much sooner and eats less at each meal.

However the new study suggests another mechanism may be at work. Cummings and colleagues believe the cells in the stomach that produce ghrelin become inactive when they are no longer exposed to food in the gut.

To test the theory, the researchers analysed blood samples from 13 obese patients before and after a six-month low-fat, low-calorie diet, and from five patients who had undergone gastric-bypass surgery within the past one to three years. Ten normal-weight patients served as a control group. The dieters lost an average of 17 percent of their body weight, and their ghrelin levels rose by about 24 per cent.

The surgery group had lost an average of 36 percent of their weight, and their ghrelin levels remarkably had sunk to 77 per cent below normal, and 72 per cent below the dieters' level.

The very low levels of the surgery group did not show the increases during pre-meal and post-meal decreases that were found in normal adults.

According to Cummings, the rise in ghrelin caused by dieting and several other forms of weight loss is part of the body's normal adaptive response.

When we lose weight, the body senses this as famine, and triggers a survival mechanism to keep our weight constant, the metabolism rate drops, and we feel hungrier, so we'll eat more.

That's the ostensible reason, notwithstanding the present new findings on the hormone ghrelin, why most diets fail.

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