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In a 104-week randomized trial, adults with overweight or obesity assigned to drink non-nutritive sweetened beverages lost a similar amount of weight to those assigned to water. Both groups maintained weight reductions, but the study tested these drinks alongside a structured behavioral program, not as a stand-alone weight-loss method.
A 104-week randomized trial found that adults with overweight or obesity who drank non-nutritive sweetened beverages lost a similar amount of weight to participants who drank water. The findings, published in the British Journal of Nutrition, add long-term clinical evidence to debate over whether diet drinks can be used during weight management.
The SWITCH trial enrolled 493 adults with overweight or obesity, all taking part in a structured behavioral weight-management program. Researchers randomly assigned participants to drink either water or commercially available diet beverages each day. The drinks included products sweetened with aspartame, acesulfame potassium or sucralose.
After 104 weeks, the diet-beverage group had lost an average of 4.8 kilograms, compared with 3.7 kilograms in the water group. Researchers reported that the difference was not statistically significant. Both groups maintained weight reductions over the two-year study, including during the final year, when participants no longer received assistance.
Participants in both groups also had reductions in waist and hip measurements, changes in body composition and improvements in several metabolic biomarkers. The researchers reported no clinically meaningful differences in measures such as blood pressure and cholesterol associated with long-term consumption of the tested sweeteners compared with water. Sugar intake fell in both groups, with a slightly greater reduction among those assigned diet beverages.
What the Results Mean for Weight Management
The results suggest that, within a supported weight-management program, diet beverages can be an alternative to water for people seeking to reduce sugar intake without undermining weight loss. The similar outcomes also speak to concerns that non-nutritive sweeteners might disrupt appetite regulation or lead to weight gain over time. In this trial, the researchers did not find evidence of those effects in the measured outcomes.
The findings do not show that diet drinks themselves caused the weight reductions. Participants received a structured behavioral program, and the comparison was between two drink assignments within that setting. The trial also does not establish that every sweetened product, dose, or pattern of use has the same effects. For readers, the practical point is narrower: among these participants, the assigned diet beverages performed similarly to water for weight outcomes over two years.
The study may inform future discussions of public-health advice. The researchers said the results add randomized clinical evidence to a debate that has also drawn on observational research. A single trial, however, does not by itself settle broader questions about long-term dietary guidance.
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How the Trial Fits the Sweetener Debate
Non-nutritive sweeteners are low-calorie or calorie-free substitutes for sugar used in many foods and drinks. Health recommendations have weighed their possible role in reducing sugar intake against uncertainty about their longer-term effects. The World Health Organization has advised against using non-sugar sweeteners for weight control, citing uncertainty in observational evidence. The SWITCH results offer a randomized comparison over two years that may contribute to future reviews of that guidance.
The research was led by Professor Jo Harrold of the University of Liverpool and Professor Jason Halford of the University of Leeds, formerly of Liverpool. The study was funded by the American Beverage Association. The source report says the researchers operated independently from the funder and retained control over analysis and reporting. The published findings build on earlier results from the SWITCH trial reported in the International Journal of Obesity in 2023.
The authors describe the work as the longest and most comprehensive randomized controlled trial to date examining non-nutritive sweetened soft drinks. That description is the researchers’ characterization. The trial tested daily commercially available beverages within a particular program and population, so its findings should be read in that scope.
“These latest findings show that concerns about sweeteners disrupting appetite or causing weight gain are not supported when tested in a rigorous, long-term randomized trial.”
— Professor Jo Harrold, University of Liverpool
Limits of the Two-Year Evidence
The reported results do not establish whether the findings apply beyond the 493 adults enrolled, or to people who are not following a structured behavioral program. The source material does not provide detailed information on participant demographics, adherence to drink assignments, or how many participants completed each stage, so those details cannot be assessed here.
The study found similar weight outcomes between the assigned groups; it does not establish that diet drinks are superior to water, or that either drink alone produces weight loss. The researchers reported that sweetener intake stayed within established European Food Safety Authority safety thresholds, but the supplied results do not give the amounts consumed or detailed results for each sweetener separately. Longer-term outcomes beyond 104 weeks also remain unknown.
The funder was the American Beverage Association. The researchers said the team worked independently and controlled analysis and reporting. The available source material does not include further details of the funding arrangements or the paper’s full disclosures, so those cannot be independently summarized here.
How Guidance Could Change
The paper, titled “Effect of non-nutritive sweetened beverages versus water on body weight: long-term results of a randomised controlled trial,” is published in the British Journal of Nutrition. The researchers said they hope the evidence will inform future WHO guidance and public-health policy. Any change to recommendations would depend on how this trial is weighed alongside other evidence, including research on different populations and outcomes.
For now, the findings describe outcomes across the trial’s two-year period. Further analysis or studies could clarify whether the similar results hold in other settings, how different sweeteners compare, and whether outcomes persist over longer periods.
Key Questions
Did diet drinks lead to more weight loss than water?
No statistically significant difference was reported. Average weight loss after 104 weeks was 4.8 kg in the diet-beverage group and 3.7 kg in the water group.
Who took part in the SWITCH trial?
The trial included 493 adults with overweight or obesity who participated in a structured behavioral weight-management program.
Which sweeteners were included?
The tested beverages included drinks containing aspartame, acesulfame potassium and sucralose.
Does the study show that diet drinks cause weight loss?
No. Participants were enrolled in a behavioral weight-management program. The trial compared drink assignments within that program and found similar weight outcomes for diet beverages and water.
Source: rss
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