Major trial examines sugar-free sweetened soft drinks
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Researchers at the University of Liverpool have conducted the longest and most comprehensive randomized controlled trial of non-nutritive sweetened (NNS) soft drinks.
Non-nutritive sweeteners are low- or no-calorie alternatives to sugar used to sweeten foods and drinks. The 104-week clinical trial shows that NNS beverages, or diet beverages, are equivalent to water for long-term weight management.
Jo Harrold, dean of psychology at the University of Liverpool, and Jason Halford, a professor of biological psychology and health behaviors at the University of Leeds and formerly of the University of Liverpool, conducted the peer-reviewed research, which was funded by the American Beverage Association. The research team was independent of the funder and had full control over the analysis and reporting of its findings.
The study was published in the British Journal of Nutrition and provides long-term clinical evidence that NNS beverages—specifically those containing aspartame, acesulfame potassium (acesulfame-K) and sucralose—are equivalent to water in supporting weight loss and long-term weight maintenance.
The SWITCH trial followed 493 adults with overweight or obesity through a structured behavioral weight management program. Participants were randomly assigned to consume either water or commercially available diet beverages daily, with sweeteners provided at levels well within established European Food Safety Authority (EFSA) safety thresholds.
Overall, the results do not support concerns that NNS beverages disrupt appetite regulation or cause long-term metabolic harm.
Key outcomes include:
- Equivalent weight loss between the NNS beverage and water groups at 104 weeks: −4.8 kg (−10.6 pounds) and −3.7 kg (−8.2 pounds), respectively, a difference that was not statistically significant.
- Sustained weight reduction over two years in both groups, even during the final unassisted year.
- Decreases in waist and hip circumference and improvements in body composition and several metabolic biomarkers in both groups.
- No clinically meaningful differences in measures such as blood pressure and cholesterol after long-term consumption of beverages containing aspartame, acesulfame-K or sucralose, compared with water.
- Decreased sugar intake in both groups, with slightly greater reductions in the NNS group.
The findings address recent World Health Organization (WHO) guidance, which advised against using non-sugar sweeteners for weight control because of uncertainty in observational studies. The SWITCH trial provides long-term evidence from a randomized controlled trial that can be used to inform global guidelines.
Harrold said, "The University of Liverpool is one of the U.K.'s leading research-intensive higher education institutions, with a key focus on public health. 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. We hope this evidence informs future WHO guidance and public health policy."
The effectS of non-nutritive sWeetened beverages on appetITe during aCtive weigHt loss (SWITCH) trial was conceived and designed by researchers seeking to reduce sugar in the diet and address questions about the potential effects of using sweeteners as a substitute on appetite regulation. This latest work builds on evidence published in the International Journal of Obesity in 2023.
Halford, of the University of Leeds and the University of Liverpool, concluded, "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."
Publication details
Joanne A. Harrold et al, Effect of non-nutritive sweetened beverages v . water on body weight: long-term results of a randomised controlled trial, British Journal of Nutrition (2026). DOI: 10.1017/s0007114526108150
Journal information: British Journal of Nutrition , International Journal of Obesity
Key medical concepts
Weight LossAppetite Regulation
Clinical categories
Weight managementNutrition & Healthy eatingPreventive medicineEndocrinologyHealthy living Provided by University of Liverpool Who's behind this story?
Swati Mestri
Swati Mestri holds a bachelor's degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space. Full profile →
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