Does drinking water promote healthy weight loss?

Most popular diet books and plans advise drinking plenty of water. Even non-dieters are admonished to drink at least eight 8-oz glasses of water a day.

But is there proof that drinking plenty of water helps lose weight? How much water should one drink?

While there’s no evidence that filling up with water will make you less hungry, and there’s no rigorous proof for the eight glasses a day advice (Why eight? Why not seven? Or eleven?) there’s actually some interesting evidence showing that drinking plenty of water helps with weight loss.

A recent article in the research journal Obesity asked whether increased intake of drinking water was associated with weight loss over a 12 month period in women randomly assigned to four different weight loss diets. The study teased apart the absolute effects of drinking water from the effect of replacing water for caloric drinks (drinking water instead of a caloric drink is expected to result in weight loss, due to reduction of caloric content).

The study was done using data from the Stanford A to Z study, which included 311 overweight women aged 25-50, and assigned participants to one of four popular weight-loss diets that are available in book form: Atkins, Zone, LEARN and Ornish. This study looked only at the women who reported a daily intake of under one liter (about four 8-oz glasses) a day when they started the diet.

The results show that an absolute increase in drinking water to one liter per day was associated with about five pounds’ weight loss over 12 months. The associations were independent of diet group, food composition, physical activity, and socio-demographic variables.

Of course, we expect that drinking water instead of caloric beverages would promote weight loss by eliminating beverage calories and lowering total energy intake. The interesting finding in this study is that there was an absolute effect of drinking water on weight loss—the authors used complicated statistical models to show that higher water intake was associated with weight loss independent of beverage calories, and that non-caloric beverages (“diet” drinks) do not have the same effect.

How can that be explained?

The authors, Jodi D. Stookey, Florence Constant, Barry M. Popkin and Christopher D. Gardner said:

“This study is limited with respect to inferences about the residual effects of drinking water after control for energy intake. Although drinking water may promote weight loss by increasing energy expenditure and/or rates of lipolysis (the break-up of fats - ed.), variables necessary to explore these pathways were not assessed in the A to Z study. Further work is needed to determine whether postprandial resting energy expenditure and/or macronutrient metabolism mediate beneficial effects of drinking water on weight loss.”

It would be interesting to see if further research will show similar results.

What’s for certain is that replacing caloric drinks with water results in a reduction of caloric intake and, if sustained over time, can lead to significant weight loss.

Accompanying the study is a disclosure, stating that three of the authors (Stookey, Popkin and Gardner) have no conflicts of interest, while Constant is an employee of Nestle's Water.

In case you’re curious to know which diet fared best in the Stanford A to Z study’s take a look here.

Whenever I read studies about weight loss diets I’m bothered by the modest results achieved by participants (typically so different from results touted in weight loss commercials) for what’s obviously a lot of dieting effort, and the knowledge that so few of the dieters will be able to maintain those losses.

It reinforces my conviction that we should really do more to promote healthy eating and healthy, active lifestyles that sidestep overweight conditions from the beginning.

Ayala