Common wisdom has long held that drinking water before meals can promote weight loss, but there were no studies proving the point. To test it, researchers at Virginia Tech in Blacksburg assigned 48 overweight or obese men and women ages 55 to 75 to one of two groups. Both groups consumed low-fat, low-calorie diets for 12 weeks, but one group was told to drink two 8-ounce glasses of water before breakfast, lunch and dinner.

"We were concerned that they might have trouble drinking this much water before each meal but they had no problems," says Brenda Davy, associate professor of nutrition and senior author of the study.

At the end of the 12 weeks, the water drinkers shed about 15.5 pounds, while the other group dropped about 11 pounds.

Davy and her colleagues found that after a year both groups succeeded in keeping the pounds off, but those who continued to drink water before meals lost even a bit more, an average of 1.5 pounds. Why is water so effective? She says it may be because it fills the stomach with a zero-calorie fluid, so people eat less.

Drinking water before meals may work only if you've reached middle age. Researchers believe that in younger people, water begins to leave the stomach almost immediately. But in older people, it takes longer for the stomach to empty so they feel full for a longer time.

"This interesting study shows that drinking water before meals provides some benefit in terms of weight loss," says Lawrence Cheskin, M.D., director of the Johns Hopkins Weight Management Center. "Clearly, any tool we have to help people feel more full has value."

The research was presented in Boston on Aug. 23 at the 2010 annual meeting of the American Chemical Society. The study was funded by the Institute for Public Health and Water Research, a nonprofit, independent science organization that was launched by an unrestricted grant from the Brita Products Co.

Nissa Simon writes about health and science in New Haven, Conn.