Q: Does drinking more water really help you lose weight?
A: In some small studies, drinking 16 ounces of water before meals has helped decrease calorie consumption and improved weight loss among middle-aged and older adults participating in weight-loss programs. It also seemed to help them maintain their weight loss after the programs ended.
We need more studies to know if this really works. If it does, it's not clear whether it would be due to reducing hunger or if it has direct effects on metabolism. You may hear claims that drinking more water will rev up your metabolism, so you lose weight by burning more calories.
However, I can find only a couple of controlled studies that tested this. These studies show a small increase in calorie burning after cold water was consumed. This involved a bit over 16 ounces of cold water in adults and proportionately smaller, but still substantial, amounts in overweight children. However, in one study, the increase in metabolic rate was minimal; in the other, although the effect was larger, it was shown only briefly. Even if repeated several times a day, researchers estimate that it would result in weight loss of a couple of pounds over a whole year.
Other claims that drinking water supports weight loss through washing out fat are not founded on research at all. It seems more likely that if drinking water works, it does so by helping you eat less. Other studies suggest that consuming more water-rich foods may be even more effective at helping reduce calorie consumption. For example, in a study in which people consumed the same amount of water at a meal as a beverage or in soup, those who ate the water-rich soup consumed fewer calories.