Study Finds Diet Soda Matches Water in Supporting Weight Loss Over Two Years

In a two-year randomized study conducted in Liverpool, England, 493 overweight or obese adults aged 18-65 were split between a water regimen and a diet-beverage regimen, each receiving 22.3 oz daily. The diet drinks contained non-nutritive sweeteners such as aspartame, acesulfame potassium and sucralose, and participants could choose from various diet sodas, low-calorie fruit drinks and flavored waters. After the 104-week period, the diet-drink cohort lost roughly 10.6 lb, while the water cohort lost about 8.2 lb, with no meaningful differences in waist, hip measurements, body-fat percentage or cholesterol.

Weight loss was sustained during the final year when formal weight-management support ceased. Researchers noted the study did not isolate the effect of the beverages themselves, as all participants received nutrition counseling and activity guidance. Limitations included a single-site design, lack of race/ethnicity data, and a dropout rate that left 220 participants completing the trial. Funding came from the American Beverage Association, though the sponsor did not influence study design or analysis.