Diet drinks match water for weight loss in two-year Liverpool trial

October 3, 2026 at 05:00 AM2 min

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A two-year randomized trial at the University of Liverpool found diet drinks containing aspartame, acesulfame-K, and sucralose performed similarly to water for weight loss and maintenance. The SWITCH trial followed 493 adults with overweight or obesity through a structured behavioral weight management program. Weight loss was comparable between groups, with no clinically meaningful differences in metabolic markers.

Key Facts

The SWITCH trial included 493 adults with overweight or obesity who participated in a structured behavioral weight management program.
After 104 weeks, weight loss was similar between the diet beverage group (−4.8 kg) and the water group (−3.7 kg), with no statistically significant difference.
The study was funded by the American Beverage Association, but researchers stated the study team operated independently and retained full control over analysis and reporting.
The findings were published in the British Journal of Nutrition and covered beverages containing aspartame, acesulfame potassium, and sucralose.
Sugar intake fell in both groups, with a slightly larger reduction among participants drinking non-nutritive sweetened beverages.

Trial Design

Researchers at the University of Liverpool completed what they describe as the longest and most comprehensive randomized controlled trial to date examining non-nutritive sweetened soft drinks. The SWITCH trial included 493 adults with overweight or obesity who took part in a structured behavioral weight management program. Participants were randomly assigned to drink either water or commercially available diet beverages each day. The amounts of sweeteners consumed remained well within established European Food Safety Authority (EFSA) safety thresholds.

Weight and Metabolic Outcomes

Weight loss was similar between the non-nutritive sweetened beverage and water groups after 104 weeks (−4.8 kg vs −3.7 kg; nonsignificant difference). Both groups maintained weight reductions across the full two-year study, including during the final year when participants no longer received assistance. Participants in both groups had reductions in waist and hip circumference, along with improvements in body composition and several metabolic biomarkers. Researchers found no clinically meaningful differences in measures such as blood pressure and cholesterol linked to long-term consumption of either aspartame, acesulfame-K, or sucralose compared with water. Sugar intake fell in both groups, with a slightly larger reduction among participants drinking non-nutritive sweetened beverages.

Sweetener Debate Context

The results are relevant to recent World Health Organization (WHO) guidance advising against the use of non-sugar sweeteners for weight control because of uncertainty in observational research. The SWITCH trial adds long-term randomized controlled evidence that may help inform future global recommendations.