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Researchers at the universities of Liverpool and Leeds have found that non-nutritive sweetened (NNS) beverages, including diet soft drinks, performed similarly to water for weight loss and long-term weight management over two years.
The findings came from a 104-week randomised controlled trial involving 493 adults with overweight or obesity. Participants took part in a structured behavioural weight-management programme and were randomly assigned to consume either water or commercially available diet beverages each day.
The study, published in the British Journal of Nutrition, is described by the researchers as the longest and most comprehensive randomised controlled trial to date examining NNS beverages.
Participants drinking NNS beverages containing aspartame, acesulfame potassium (acesulfame-K) or sucralose lost a similar amount of weight to those drinking water after 104 weeks. Average weight loss was 4.8 kg in the NNS group and 3.7 kg in the water group, with the difference not statistically significant.
Both groups maintained their weight reductions throughout the two-year study, including the final year when participants were no longer receiving assistance.
Researchers also found reductions in waist and hip circumference, improvements in body composition and changes in several metabolic biomarkers in both groups.
There were no clinically meaningful differences in measures such as blood pressure and cholesterol associated with long-term consumption of the sweeteners compared with water. Sugar intake declined in both groups, although the reduction was slightly greater among those consuming NNS beverages.
The study also found no evidence that the beverages interfered with appetite regulation or caused long-term metabolic harm.
Professor Jo Harrold of the University of Liverpool led the research with Professor Jason Halford of the University of Leeds, who was formerly at Liverpool. The study was funded by the American Beverage Association, while the researchers said the study team worked independently from the funder and retained control over the analysis and reporting.
The findings add to the debate over the role of non-sugar sweeteners in weight management. The World Health Organization has previously advised against using non-sugar sweeteners for weight control, citing uncertainty in evidence from observational studies.
Harrold said the findings did not support concerns that sweeteners disrupt appetite or cause weight gain when examined in a rigorous, long-term randomised trial.
Halford said the study provided long-term clinical evidence that had been missing from international discussions and suggested NNS beverages could provide an alternative to sugar-sweetened drinks for people managing their weight.
The SWITCH trial was designed to examine whether reducing dietary sugar affects weight management and whether replacing sugar with NNS changes appetite regulation. The latest findings build on earlier results from the trial published in the International Journal of Obesity in 2023.