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Scientists have found that dieters who drink two 250-millilitre glasses of water right before their meals tend to lose more weight than those who don't drink before meals but who eat similar diets.

Most of us know that drinking a lot of water can make us feel full. But there has been little research until now on whether water can't actually help with weight loss.

Now, researchers led by Brenda Davy, with Virginia Tech in Blacksburg, Va. have conducted the first randomized controlled trial on how drinking water can affect weight.

They divided 48 older adults, aged 55-75 years, into two groups: one group drank two cups of water prior to every meal, while the other did not. All of the subjects ate a low-calorie diet during the study.

Over 12 weeks, the water drinkers lost about 7 kilograms (15.5 pounds), while the non-water drinkers lost only about 5 kg (11 pounds).

The data was presented this week at the 240th National Meeting of the American Chemical Society (ACS).

Davy thinks water may help with weight loss simply because it fills the stomach and helps people feel full so they eat less calorie-containing food during their meal. The researchers found that the water drinkers ate nearly 100 fewer calories at each meal. Over time, that deficit added up to weight loss.

Water drinkers might also lose more weight because of what they're not drinking: sweetened drinks. Davy notes that drinks sweetened with sugar and corn syrup can be high in calories. A 12-ounce can of regular pop, for instance, contains about 10 teaspoons of sugar and about 150 calories. Even a 250-ml glass of milk contains 120 calories.

Davy says the water drinkers also noticed other benefits.

"Many of our participants in the water group commented they felt they were thinking a lot more clearly; their memory was better," she says.

Dr. Stanley Bernstein says he's not surprised by the study's findings. Bernstein, the founder of a chain of weight loss centres, says he has long encouraged dieters to drink lots of water not only because it relieves water retention, but because "the more you drink, the more your system can work to break down fat."

"Drinking a lot of water is a very necessary part of losing weight. Period. It's probably, from my point of view, as effective as most diet pills," he told CTV News.

With a report from CTV's medical specialist Avis Favaro and producer Elizabeth St. Philip