Does the Recommendation to Drink 8 Cups of Water Per Day Promote Weight Loss?

Background Advice to increase water intake – typically to 8 cups per day – is frequently provided as part of a weight‐reducing diet. However, there are limited experimental data regarding the effect of increased water intake on body weight, and virtually none in the pediatric age range. Objective: To conduct a pilot study comparing two standard weight loss diets, either with (Experimental) or without (Control) additional advice and behavioral support to increase habitual water intake to 8 cups per day. Methods: A 6‐month RCT of 38 overweight and obese adolescents who consumed 蠄 4 cups of water per day at screening. The diet used for the Experimental and Control groups was identical, consisted of monthly dietary counseling with a registered dietitian, daily text messages, and a cookbook of recipes and health guides. Outcomes were assessed prior to randomization and at the end of the intervention period. Results: Reported water intake increased by 1.6±0.7 cups per day in the Experimental vs. Control group (P=0.03). Urine specific gravity, a biomeasure of hydration status, decreased significantly in the Experimental group (‐0.007±0.003, P=0.012), but did not change in the Control group. BMI z‐score did not differ between groups (‐0.10±0.03 vs. ‐0.09±0.03; P=0.88, respectively). No significant group differences were seen in other cardiometabolic risk factors. Conclusion This pilot study provides preliminary evidence that advice to increase water intake to 8 cups per day, as part of a standard weight‐reducing diet, does not produce additional weight reduction in adolescents. Research Support: New Balance Foundation, Airborne Cy Pres Fund, NIDDK Grant K24DK082730