High-protein diets boost hunger-taming hormone.

Eating protein appears to boost blood concentrations of a hormone recently found to restrict appetite, researchers report. The findings could explain the success of popular high-protein diets.

Four years ago, Rachel L. Batterham of University College London and her colleagues found that injecting a hormone called peptide YY (PYY) into both normal-weight and obese people reduced their food intake by about a third and dampened hunger. A person's gut normally secretes the hormone during and after a meal.

Batterham's team wondered whether food's three basic nutrients--protein, carbohydrates, and fat--have different effects on how much PYY people secrete.

To find out, the researchers recruited groups of normal-weight and obese men. Each volunteer came into Batterham's lab and ate a specially crafted meal on three days. Although the three meals tasted similar and had the same number of calories, each meal offered a proportion of calories from protein, carbohydrates, and fat.

The researchers found that blood concentrations of PYY were significantly higher in both groups of men after the high-protein meal than after meals high in carbohydrates or fat. Both groups reported higher sensations of fullness and less hunger after eating more protein.

Working with normal and obese mice, the researchers found that animals fed high-protein diets gained less weight and made more PYY than those fed more carbohydrates or fat. However, animals genetically modified to produce no PYY gained similar amounts of weight, regardless of their diets' composition.

Batterham's team suggests in the September Cell Metabolism that people can harness the appetite-decreasing power of PYY simply by boosting their dietary protein.--C.B.