Researchers at the University of Liverpool have conducted the longest and most comprehensive randomised controlled trial on 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 NNS beverages i.e. diet beverages are equivalent to water for long term weight management.
Professor Jo Harrold, Dean of Psychology at the University of Liverpool alongside Professor Jason Halford, Professor, Biological Psychology & Health Behaviours at the University of Leeds (formerly of the University of Liverpool) conducted the peer-reviewed research funded by the American Beverage Association. The research team was independent of the funder and had full control over the analysis and reporting of their findings.
The major new 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 behavioural weight management programme. Participants were randomised 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 have long term metabolic harm.
Key outcomes include:
Importantly, the findings directly address recent World Health Organization (WHO) guidance, which advised against using non-sugar sweeteners for weight control due to uncertainty in observational studies. The SWITCH trial provides long-duration, randomised controlled evidence which can be used to inform global guidelines.
Professor Joanne Harrold , said: “The University of Liverpool is one of the UK’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 randomised 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 in the context of the need to reduce sugar in the diet and to address questions about the potential effects on appetite regulation of using sweeteners as a substitute. This latest published work continues from previously published evidence in the International Journal of Obesity in 2023.
Professor Jason Halford, University of Leeds and 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.”
The paper, ‘ Effect of non-nutritive sweetened beverages versus water on body weight: long-term results of a randomised controlled trial ’, was published in British Journal of Nutrition (DOI: https://doi.org/10.1017/S0007114526108150 ).
British Journal Of Nutrition
People
Effect of non-nutritive sweetened beverages versus water on body weight: long-term results of a randomised controlled trial
4-Aug-2026