Protein Triggers Weight Loss Hormone

Eating protein triggers a natural weight-loss hormone, British researchers say.

When released in the gut, the hormone known as PYY reduces hunger. And high-protein foods set off PYY better than other foods, according to Rachel L. Batterham, M.D., of University College London, and colleagues.

Recent studies suggest PYY is part of the solution to obesity. Compared with a normal-weight person, for example, an obese person has to eat twice as many calories to trigger PYY.

"We've now found that increasing the protein content of the diet augments the body's own PYY, helping to reduce hunger and aid weight loss," Batterham says, in a news release.

If this sounds like the Atkins Diet, Batterham and colleagues say it's not. They note that many people on the Atkins Diet eat a lot of saturated fat as well as a lot of protein.

Obesity, Men, And Mice

Is PYY really the key to obesity? Batterham's team first looked at what kind of food best satisfies hunger. They studied nine obese men and 10 normal-weight men. After brief fasts, the men ate different meals. Each of the meals — a high-protein meal, a high-fat meal, and a high-carbohydrate meal — had the same number of calories.

All the men said the high-protein meal best satisfied their hunger. Interestingly, the normal-weight men found the high-fat meal more satisfying than the high-carb meal, while the obese men did not.

Measurements showed the high-protein meal triggered the most PYY in all of the men. In the normal-weight men — but not the obese men — the high-fat meal triggered more PYY than the high-carb meal.

Batterham's team genetically engineered a mouse strain that did not have the PYY gene. These mice ate huge amounts of food, and quickly became obese.

Normally, obese mice fed a high-protein diet will eat less and lose weight. But a high-protein diet didn't help the PYY-defective mice lose weight — unless they also got PYY treatments.

Hunters Vs. Farmers

Why does protein trigger PYY and satisfy hunger so well? It's not entirely clear. But Batterham and colleagues suggest we blame our ancestors.

The prehistoric humans whose genes we inherit had a different diet than we do. They got 19 percent to 35 percent of their energy from protein and 22 percent to 40 percent from carbs. Our modern diet gets 49 percent of its energy from carbs and only 16 percent protein.

"One potential weight loss strategy is therefore to increase the satiating power of the diet and promote weight loss through the addition of dietary protein — harnessing our own satiety system," Batterham says. "Such a diet is perhaps more typical to that of our hunter-gatherer ancestors."

The findings appear in the September issue of the journal Cell Metabolism.

SOURCES: Batterham, R. Cell Metabolism, September 2006; vol 4: pp. 223-233. News release, Cell Press.

By Daniel DeNoon
Reviewed by Louise Chang
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