Many popular diets claim that changing the proportion of carbohydrates, proteins, and fats you eat can bring about weight loss. Now, a new study has shown how this may work.

The study examined how well different nutrients suppress ghrelin, an appetite-stimulating hormone secreted by the stomach.

When fat is consumed, ghrelin levels remain relatively high, as does appetite. But eating protein actually suppresses the hormone and along with it, hunger.

Study subjects were given three drinks with widely varying compositions of carbohydrates, fats, and proteins. Blood samples were taken before the first beverage was ingested and every 20 minutes for six hours thereafter. Researchers then measured the ghrelin levels in each sample.

According to one of the study's authors, Dr. Karen Foster-Schubert of the University of Washington School of Medicine in Seattle, Washington, eating protein "resulted in the greatest suppression of ghrelin over a long period." What was really noteworthy, however was what happened when subjects ate carbohydrates. Initially, the carbohydrates strongly suppressed ghrelin -- the reason why so many of us don't feel full unless we've eaten some starch. But carbohydrates had a rebound effect, Ghrelin levels shot back up, rather than staying low as they did when subjects ate protein.

"These findings open the door to future research on the effectiveness of varying methods of dieting," said Foster-Schubert. For dieters, it may mean that that piece of bread that seems to fill you up at noon will leave you hungrier at 3 o'clock.

A version of this paper has been published on-line and the full paper will appear in the April 2008 issue of JCEM, a publication of The Endocrine Society.