A two-year randomized trial led by researchers at the University of Liverpool has found that diet beverages sweetened with non-nutritive sweeteners worked about as well as plain water for long-term weight loss, adding new controlled-trial evidence to a long-running public health debate over artificial sweeteners.
The trial, known as SWITCH, followed 493 adults with overweight or obesity through a structured weight-management program, randomly assigning them to drink either water or commercially available diet beverages sweetened with aspartame, acesulfame-K or sucralose. After 104 weeks, the two groups had lost statistically similar amounts of weight — an average of 4.8 kilograms in the diet-beverage group versus 3.7 kilograms in the water group, a gap the researchers said was not statistically significant. The results were published in the British Journal of Nutrition.
Testing sweetener concerns directly
Both groups maintained their weight loss through the full two years, including a final year in which participants received no further support from the research team. Beyond the scale, both groups saw reductions in waist and hip circumference and improvements in body composition and several metabolic markers, with no clinically meaningful differences in blood pressure or cholesterol tied to any of the three sweeteners tested. Sugar intake fell in both groups, slightly more so among those drinking diet beverages. All participants' sweetener intake stayed within safety limits set by the European Food Safety Authority.
The findings speak directly to 2023 World Health Organization guidance advising against non-sugar sweeteners for weight control, a recommendation the WHO itself acknowledged rested largely on lower-quality observational studies rather than long-term controlled trials. "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," said Jo Harrold, a professor of psychology at the University of Liverpool who led the research with Jason Halford of the University of Leeds. "We hope this evidence informs future WHO guidance and public health policy."
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.
Jason Halford, University of Leeds
One caveat worth weighing: the trial was funded by the American Beverage Association, the U.S. soft-drink industry's trade group, though the university says its researchers kept independent control over the study's design, analysis and reporting. The trial also builds on earlier interim results the same team reported previously, and like any single trial, its findings will need to be weighed alongside other research before global guidance changes. The authors say they hope the two-year data will nonetheless factor into any future revision of WHO sweetener guidance.
