A new randomized controlled trial from the University of Liverpool provides long-term evidence that diet soft drinks can support weight loss as effectively as water. The SWITCH trial followed 493 adults with overweight or obesity for 104 weeks, assigning them to drink either water or commercially available beverages sweetened with aspartame, acesulfame-K, or sucralose as part of a structured weight management program. Weight loss in the diet-drink group was 4.8 kg on average, compared with 3.7 kg in the water group—a difference that was not statistically significant.
Both groups maintained their weight reductions through the second year, even after structured assistance ended. Participants also showed similar improvements in waist and hip circumference, body composition, and several metabolic biomarkers. The researchers found no clinically meaningful differences in blood pressure or cholesterol between the groups, and sugar intake fell in both, with a slightly larger drop among those drinking diet beverages.
The findings, published in the British Journal of Nutrition, directly address recent World Health Organization guidance that advises against using non-sugar sweeteners for weight control based largely on observational research. The authors say this trial supplies the long-term randomized evidence that has been missing from international debates. The study was funded by the American Beverage Association, though the research team notes it operated independently and retained full control over analysis and reporting.