Dieters who drink more water have greater weight loss, according to a new review of several prior studies.
In one study that asked dieters to drink water before a meal, for instance, "the water enhanced the weight loss," said Brenda Davy, a professor at Virginia Tech who led some of the work included in the review.
Researchers said there is not yet enough evidence, however, to say for sure that drinking more water will help people shed the pounds.
Rebecca Muckelbauer, a researcher at the Berlin School of Public Health, Charité University Medical Center Berlin in Germany, led the new review of the water studies.
She said that, as a nutrition researcher, people had often asked her about whether they should drink water to lose weight, and she didn't know the answer.
She and her colleagues decided to examine all of the studies on weight and water consumption.
Eleven studies fit their criteria.
Three of them showed that increased water intake among dieters was tied to greater weight loss.
A study by Davy's group found that middle aged and older adults who drank two cups before a meal lost about four pounds more than a group that didn't drink the extra water.
Yet another study found that women who increased their water consumption while they dieted lost more weight than those who kept it below one liter a day.
It's not clear how water might help people shed pounds.
One possibility, said Davy, is that water could squelch feelings of hunger.
"This may have helped them reduce their calorie intake," she told Reuters Health.
Muckelbauer agreed that increased fullness is the most likely explanation, but another possibility is something called "water-induced thermogenesis."
The idea is that "drinking water itself increases energy expenditure of your body. It has an energy consuming effect. This is not very well studied," Muckelbauer told Reuters Health.
The Institute of Medicine recommends that adults consume between 91 ounces of water for women and 125 ounces for men (2.7 - 3.7 liters) each day, but this total can come through food, plain water or other beverages.
While the experimental studies suggest that drinking water may aid in weight loss, the surveys Muckelbauer examined don't always show that people who drink more water are slimmer.
In fact, some found that obese or overweight adults drank more water than people of normal size, while others did not find such a link, Muckelbauer's team reports in the American Journal of Clinical Nutrition.
"We don't have conclusive evidence that increasing water intake reduces weight, but there are certainly other benefits to increasing our intake," said Davy.
She said people in the U.S. typically drink about 400 to 500 calories a day from other beverages, and replacing them with water is not a bad idea.
One study found that women who drink water, rather than sweet drinks, had a slightly lower chance of developing diabetes.
And women who don't drink plenty of water have greater odds of getting kidney stones.
"There's not a lot of risk for recommending (increased water intake) for individuals," Davy said.
Muckelbauer said it will be helpful to have larger experiments looking at the potential weight loss benefits of adding more water to the diet.