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Last Updated: Wednesday, 9 November 2005, 07:35 GMT
Why high protein diet fills us up
Meat is a rich source of protein
Scientists believe they may have cracked the reason why protein-rich diets, such as Atkins, curb hunger.

They have discovered the diets spark glucose production in the small intestine - a phenomenon which leads to us feeling full.

The researchers, from the French research body INSERM, say the findings may help the development of new treatments for eating disorders.

The study, on rats, is published in the journal Cell Metabolism.

Appetite is controlled by many neurochemical and hormonal signals, quite apart from psychological factors and social aspects
Dr Toni Steer

It is well known that eating a protein-based diet reduces hunger pangs, and leads to people eating less food.

However, the mechanism by which proteins depress appetite has been unclear.

Previous research has found that a rise in dietary protein has little effect on the major hormones that regulate hunger.

The INSERM team found that feeding rats a high protein diet significantly increased the activity of genes involved in glucose production in the animal's small intestine.

Signals to the brain

This led to increased glucose production, which was sensed by the liver, and relayed to the brain, causing the animals to cut their food intake.

The researchers, led by Dr Gilles Mithieux, say they do not know how protein would trigger increased glucose production.

But they believe it may trigger the release of chemical inside the cells called cyclic AMP, which can stimulate the genes responsible for producing glucose.

Dr Simon Langley-Evans, an expert in human nutrition at Nottingham University, said: "Diets like Atkins do appear to promote weight loss because they stop hunger.

"It appears to be nothing to do with the metabolic processing of protein, but because people following these diets simply eat less.

"It makes sense that if proteins do somehow increase the production of glucose in the small intestine that this would act on neuropeptides that would send signals to the brain that the stomach is full."

However, Dr Langley-Evans said glucose production was also stimulated by a low carbohydrate diet.

He said: "How specific is this effect to a high protein diet - can the same effect be shown with a high fat diet?"

Dr Toni Steer, a nutritionist at the Medical Research Council Human Nutrition Research Unit, said further studies would be needed to pin down the effect in humans.

She said "This is unlikely to be the whole story. Appetite is controlled by many neurochemical and hormonal signals, quite apart from psychological factors and social aspects."

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