Diet Drinks Equal Water for Weight Loss, SWITCH Trial Finds

A 104-week clinical trial published in the British Journal of Nutrition reveals that non-nutritive sweetened soft drinks perform equivalently to water for long-term weight management, offering new data for adults with overweight or obesity.

Following 493 participants with a body mass index between 27 and 35, the SWITCH trial was conducted by researchers at the University of Liverpool and the University of Leeds. Adults working through a structured behavioral weight management program achieved similar weight loss over two years whether they drank water or beverages containing low- and no-calorie sweeteners. The findings provide long-term clinical data on diet beverages sweetened with aspartame, acesulfame potassium, and sucralose.

Observational studies occasionally tied diet beverages to weight gain, while the World Health Organization advised against using non-sugar sweeteners for weight control due to underlying data uncertainties. This trial was designed to test those exact concerns.

Diet Drinks Equal Water for Weight Loss, SWITCH Trial Finds — Photo: UA.NEWS

Evaluating Weight Loss Results Across Two Years of the SWITCH Trial

Participants in the diet beverage group lost an average of 4.8 kg at the conclusion of the 104-week study, compared to an average loss of 3.7 kg in the water group. Researchers noted that the 1.1-kg difference between the two regimens was statistically non-significant.

Both cohorts maintained their weight reductions across the entire two-year duration, including through the final unassisted year when participants no longer attended regular program sessions. Participants in both groups also recorded reductions in waist and hip measurements alongside positive changes in body composition. Sugar intake declined in both groups, with a slightly larger drop observed among those drinking diet beverages.

Metric at 104 Weeks	Water Group	Diet Beverage Group
Mean Weight Loss	-3.7 kg	-4.8 kg
Waist Circumference Reduction	-4.5 cm	-5.5 cm
Hip Circumference Reduction	-2.7 cm	-3.1 cm

Sweetened Beverages Perform Equivalently to Water for Weight Management

Sweetener consumption levels throughout the trial remained well within the established safety thresholds defined by the European Food Safety Authority. The study directly addresses questions surrounding whether non-nutritive sweeteners interfere with appetite control or cause metabolic harm.

Diet Soda vs Water for Weight Loss: 2-Year Trial Results

“This study provides the long-term clinical evidence that has been missing from international discussions. For people trying to manage their weight, non-nutritive sweetened beverages offer an effective alternative to sugar-sweetened drinks — and perform equivalently to water over two years.”

Professor Jason Halford, University of Leeds and University of Liverpool

Researchers hope the findings will help inform future global recommendations and public health frameworks.

American Beverage Association Funded Study with Limited Participant Data

Funded by the American Beverage Association, the research team operated autonomously from the funder to ensure scientific independence, retaining full control over study design, data analysis, and the preparation of the manuscript.

Out of the initial 493 participants, exactly 220 completed the full two-year weight measurement follow-up. Conducted at a single site in England, the trial did not record participant race or ethnicity data, which may limit how broadly the findings apply.

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