There’s really nothing new about the long-standing weight loss tip to drink more water—except that now it’s backed up by pretty compelling research. New, unpublished clinical evidence shows that drinking water prior to eating can be an effective weight loss tool. Findings of the study, led by Brenda Davy, PhD, RD, associate professor in the department of human nutrition, foods and exercise at Virginia Tech, were presented at the 240th National Meeting of the American Chemistry Society in late August.

Davy and colleagues presented results of the first randomized, controlled intervention trial demonstrating that increased water consumption is an effective weight loss strategy. The researchers had found in earlier studies that middle-aged and older people who drank 2 cups of water right before a meal ate 75–90 fewer calories during that meal. In this recent study, they found that over the course of 12 weeks, dieters who drank water before meals three times per day lost about 5 pounds more than dieters who did not increase their water intake.

The study included 48 adults aged 55–75 years, divided into two groups. One group drank 2 cups of water prior to their meals, while the other did not. All of the subjects ate a low-calorie diet during the study. Over the course of 12 weeks, water drinkers lost about 15.5 pounds, whereas non-water-drinkers lost about 11 pounds.

Davy pointed out that folklore and everyday experience long have suggested that water can promote weight loss. But there has been surprisingly little scientific information on the topic. Previous studies have hinted that drinking water before meals reduces calorie intake. Lacking until now, however, has been the “gold-standard” evidence from a randomized, controlled clinical trial that compares weight loss among dieters who drink water before meals with those who do not.

Davy says water may be so effective simply because it fills up the stomach with a substance that has zero calories. People feel fuller as a result and eat less calorie-containing food during the meal. Increased water consumption may also help people lose weight if they drink it in place of sweetened calorie-containing beverages, she said.