If you’re trying to lose weight, does it actually matter whether you reach for a low- or no-sugar beverage instead of a glass of water?  A recent clinical trial has a clear answer: no. The two-year SWITCH trial, the longest randomized controlled trial of its kind, found that beverages sweetened with non-nutritive sweeteners (NNS) performed just as well as water for long-term weight management – a finding that addresses a call by the World Health Organization (WHO) for more long-term, high-quality research on whether sweeteners can help with weight management.

Key Takeaways

• The two-year SWITCH trial followed 493 adults in a structured weight-management program, making it the longest, most rigorous head-to-head comparison of zero-sugar beverages and water to date.
• Zero-sugar beverage drinkers lost about 10.5 pounds (4.8 kg) on average, compared with about 8 pounds (3.7 kg) for water drinkers.
• Both groups stayed within healthy ranges for blood pressure and cholesterol, and saw similar improvements in body composition, with no evidence of long-term harm from zero-sugar beverages.
• Zero-sugar beverage drinkers did not increase sugar intake from foods or other beverages; sugar consumption fell in both groups, with a slightly larger drop among the group that consumed beverages with low- and no-calorie sweeteners.
• The results provide exactly the kind of high-quality, long-term, randomized evidence that the WHO's 2023 guidance on non-sugar sweeteners said was missing.

The SWITCH Trial: The Longest Randomized Controlled Trial on Zero-Sugar Beverages and Weight Loss   

The SWITCH trial is the longest and most comprehensive randomized controlled trial (RCT) to date on beverages with low- and no-calorie sweeteners, following participants for 104 weeks. Professor Jo Harrold of the University of Liverpool and Professor Jason Halford of the University of Leeds led the research and published their findings in the British Journal of Nutrition.

Researchers randomly assigned 493 adults who were overweight or obese to a structured weight-management program. Each participant drank either water or zero-sugar beverages sweetened with aspartame, acesulfame-K or sucralose, every day. The trial builds on earlier SWITCH results published in 2024, extending the trial to a full two years, including a final year in which participants received no program support, a useful test of whether earlier results would hold up on their own.

American Beverage (AB) funded the research. Consistent with standard practice for industry-funded science, AB had no role in the trial’s design, data collection, analysis or interpretation. The research team retained full control over the study and its findings throughout.

The Two-Year Results: Zero-Sugar Beverages Matched Water for Weight Loss, With No Signs of Harm  

After two years, both groups achieved similar weight loss and maintained those results, including through the final year when participants no longer received program support. The zero-sugar beverage group lost about 10.5 pounds (4.8 kg) on average, compared with about 8 pounds (3.7 kg) in the water group – a difference that researchers found was not statistically significant.

Beyond weight loss, both groups saw reductions in waist and hip measurements, improved body composition and favorable metabolic changes, with no evidence of long-term harm. Blood pressure and cholesterol stayed within healthy ranges throughout, with no clinically meaningful differences between the zero-sugar beverage and water groups.

WHO’s 2023 Guidance: Challenged by Rigorous Study

In 2023, the World Health Organization advised against using low- and no-calorie sweeteners for weight control, citing low-certainty evidence drawn largely from observational studies rather than randomized trials. The SWITCH trial adds exactly the kind of rigorous long-term, randomized evidence that WHO sought to give consumers and policymakers a clearer, more rigorous picture of how diet beverages compare with water over time.

More Choices, Backed by Science 

America’s beverage companies have spent decades expanding their low- and no-sugar options to support consumers in their efforts to achieve balance. AB supported this research to give consumers clear, science-backed information to help them make the choices that are right for them.