Drink More Water, Lose More Weight? A Study in Overweight Teens

William T. Basco, Jr., MD, MS


July 26, 2017

Is Increased Water Intake Associated With Teen Weight Loss?

Many professionals recommend increasing daily water intake as a method to limit weight gain, although the practice has little experimental data to support it.[1] The theory that increasing water intake has the potential to limit weight gain may have been extrapolated from cross-sectional studies that demonstrated that children and adolescents who took in more water had lower body mass index (BMI).

To test this theory, a recent randomized trial[1] sought to evaluate increased habitual water intake for 6 months as an intervention to promote weight loss among adolescents. Participants (n = 38) were randomly assigned to intervention or control groups, both of which received a standardized weight-reducing dietary intervention. The intervention group was also encouraged to increase water intake to 8 cups daily (and received filtering water pitchers and a water bottle to facilitate this intake) but the control group received no such encouragement. Participants (n = 38) were aged 12-17 years and were at least at the 85th percentile for BMI. The standardized dietary intervention for both groups included monthly individual dietary education by a nutritionist, physical activity recommendations, and behavioral counseling (six total sessions) along with daily text messages to the participants. In the course of the monthly sessions, the investigators ascertained how well the teens adhered to these interventions.

At enrollment, the two groups drank approximately 2.1 cups of water per day. Over the course of the study, the water intervention group reported a daily intake of water that averaged 1.6 cups more than the control group's intake. At study end, the water intervention group participants drank an average of 4.8 cups of water daily.

For the main outcome, there was no difference in the change of BMI z-score between the two groups. However, both groups experienced some improvement, with an average reduction in BMI z-score of 0.1. In weight terms, the mean weight change among both groups was less than 1 kg (-0.6 kg in the control group and -0.4 kg in the water group). No significant correlation was found between changes in BMI z-score, water intake, or urine specific gravity.

The authors concluded that encouraging 8 cups of water intake daily by overweight and obese adolescents did not show a benefit over dietary counseling and support.


This was probably a difficult trial to complete, given the intensity of the intervention. Considering that both groups experienced a very intensive dietary intervention, with monthly meetings with nutritionists, it is quite possible that the intensity of the dietary intervention masked any improvement that resulted from increased water intake. Providers should be careful not to overinterpret the negative results of this trial. Certainly, the trial shows that one can't be overconfident in suggesting increased water intake as a weight loss recommendation, but given the relatively low baseline water intake in the groups, recommending that adolescents drink more water is nevertheless not a bad idea.


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