People trying to lose weight may not necessarily have to give up diet soft drinks, after a two-year clinical trial found that beverages sweetened without sugar produced weight-loss results comparable to drinking water when both were used as part of a structured weight-management program.
The findings came from the SWITCH trial, a randomized controlled study involving 493 adults aged 18 to 65 who were overweight or obese. The research was published in the British Journal of Nutrition in August 2026 and compared non-nutritive sweetened beverages with water over a 104-week period.
Participants were randomly assigned to either a water group or a group consuming beverages made with non-nutritive sweeteners commonly used in diet and zero-sugar drinks. They were asked to drink at least two 330-milliliter servings of their assigned beverage each day while following the same behavioral weight-management program.
The program began with 12 weeks of weekly weight-loss sessions, followed by 40 weeks of monthly support focused on maintaining progress. Participants then spent the final 52 weeks without regular weight-management sessions, allowing researchers to assess longer-term results.
At the end of the two-year period, participants in the diet-drink group had maintained an average weight loss of 4.8 kilograms from their starting weight, compared with 3.7 kilograms among those assigned to water.
Researchers found that the difference between the two groups was not statistically significant, meaning neither beverage showed a clear advantage in long-term weight loss.
The study also measured waist and hip circumference, body composition, hunger and sugar intake. Both groups recorded reductions in waist and hip measurements, while body-composition testing among somr participants showed reductions in body fat.
Hunger increased slightly in both groups over the course of the trial, but researchers found no significant difference between them. Sugar intake also fell in both groups.
Researchers said the findings do not show that diet soft drinks themselves cause weight loss, since participants were also following dietary and lifestyle guidance as part of the broader program.
