Diet beverages are equivalent to water for long-term weight management, according to the longest and most comprehensive randomised trial of non-nutritive sweetened soft drinks.

The SWITCH trial followed 493 adults with overweight or obesity through a structured weight-management programme for 104 weeks. Participants were randomised to drink either water or commercially available diet beverages daily.

After two years, average weight loss was 4.8 kg in the diet-beverage group and 3.7 kg in the water group, a difference that was not statistically significant. Both groups sustained their weight reduction, including during the final year without the structured intervention.

The study was published in the British Journal of Nutrition. The sweeteners studied, aspartame, acesulfame-K and sucralose, were within European safety limits.

Professor Jason Halford said the study provides the long-term clinical evidence missing from international discussions. The trial was funded by the American Beverage Association, with the research team independent of the funder.