Data from short-term experiments suggest that drinking water may promote weight loss.
Absolute increase in water intake (drinking water in itself) alters the metabolism whereas relative increase in water intake (drinking water instead of caloric beverages) lowers the total energy intake. Thus, both increases may contribute to weight loss. However, the long-term effects of drinking water on changes in body weight or composition are unknown.
By performing secondary analysis of data from the Stanford A TO Z trial, the authors tested for associations between absolute and relative increases in drinking water and weight loss over 12 months. The A TO Z trial is a weight loss intervention study that allocates randomly overweight women to four different weight loss diets. The analysis focused only on 173 overweight premenopausal women (25-50 years old) who reported drinking less than 1 L of water at baseline. Diet, physical activity, body weight, percentage of body fat, and waist circumference were assessed at baseline, 2, 6, and 12 months.
After 2 months of diet, the water intake increased significantly both in absolute and relative terms. These changes in the beverage pattern persisted from 2 to 12 months, despite recidivism. Water intake rose on average from 30% of total beverage consumption at baseline up to 46% at 12 months, while sweetened caloric beverages decreased from 26% to 16% of total beverage consumption. Meanwhile, the average body weight loss reached approximately 3 kg after the 2 month-diet, and remained at this level over the follow-up period. Significant changes in waist circumference and body fat occurred in parallel of the changes in body weight. Over time, drinking more than 1 L of water per day as well as relative increases in drinking water were associated with significant decreases in body weight, waist circumference and body fat. The associations were independent of diet group, food composition, physical activity, and sociodemographic variables. Drinking unsweetened caloric and noncaloric beverages instead of the sweetened caloric ones was associated with a 30% smaller effect than drinking water.
Even if the observed effects of drinking water were robust, the Stanford A TO Z study was not designed to test specific effects of drinking water on weight loss. Further studies are needed to confirm these findings.
Key messages: Over time, drinking water may promote weight loss in overweight dieting women.