Diet Soda as Effective as Water for Weight Loss in New Study

Diet drinks containing sugar substitutes were found to be as effective as water for supporting weight loss in overweight or obese adults, according to a two-year randomized trial.

The study, conducted by the University of Liverpool, England, involved 493 participants aged 18 to 65 with a body mass index (BMI) between 27 and 35. Half of the participants consumed 22.3 ounces of water daily, while the other half received the same amount of diet sodas, low-calorie fruit drinks, or flavored waters sweetened with non-nutritive sweeteners like aspartame, acesulfame potassium, and sucralose. This was maintained for 104 weeks.

After two years, the group consuming diet beverages lost an average of 10.6 pounds, compared to 8.2 pounds lost by the water-drinking group. Both groups maintained a significant portion of their weight loss even in the final year of the study, which occurred after regular weight-management support ceased.

Participants in both groups also experienced reductions in waist and hip circumference and decreased body fat, with no significant differences noted between those consuming diet drinks and those drinking water. Total cholesterol levels remained within a healthy range for both groups.

Researchers noted that the study did not demonstrate that diet beverages themselves caused weight loss, emphasizing that all participants were engaged in a structured weight-management program that included nutritional counseling, behavioral support, and physical activity recommendations. A registered dietitian not involved in the study suggested that the benefit of diet beverages likely stems from substitution, replacing higher-calorie sugary drinks, rather than a direct metabolic effect.

The findings were published in the British Journal of Nutrition. The study specifically compared diet beverages with water, rather than sugar-sweetened drinks, to assess whether artificial sweeteners might impede weight loss efforts. The dietitian added that while water is still recommended as the primary hydration choice, individuals need not fear diet drinks for potentially hindering fat loss or causing weight gain.

Limitations of the research include its single-location setting in England and the absence of race and ethnicity data, which may affect the generalizability of the findings. Furthermore, only 220 of the initial 493 participants completed the full 104-week assessment, and the voluntary nature of the second-year extension could mean those who continued were more motivated.

The study received funding from the American Beverage Association, though the authors stated the association did not participate in the study's design, data analysis, or interpretation.