You have probably reached for a diet soda thinking it would help you drop a few pounds. The whole shelf has been built around that idea. For many people, that choice feels like a small, sensible one.
A new two-year randomized trial published in the British Journal of Nutrition tested the idea head to head. People who drank at least two diet drinks a day lost about the same amount of weight as people who drank plain water.
The water group ended the two years down 3.7 kilograms, or about 8 pounds. The diet-drink group was down 4.8 kilograms, roughly 10.6 pounds. The 1.1-kilogram gap was not statistically significant, which means it could easily have come down to chance.
What the trial actually asked
The study was called SWITCH and was run by researchers at the University of Liverpool. They enrolled 493 adults in Merseyside, England, who were overweight or had mild obesity.
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Everyone joined the same structured weight-loss program. There were weekly group meetings for the first 12 weeks, then monthly meetings for most of the first year. In the second year, participants were on their own, with monitoring but no coaching.
Each person was asked to drink at least two servings of their assigned beverage every day. The diet group drank cola, soft drinks or flavored water sweetened with sucralose, aspartame or acesulfame potassium. The water group drank plain water.
Of the 220 people who finished the full two years, more than 98 percent were still following the rule at week 104.
Where the result sits in a wider debate
The finding runs against guidance published in May 2023 by the World Health Organization, which advised against using non-sugar sweeteners for weight control.
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That guideline cited low-certainty evidence that long-term use of these sweeteners did not help with weight and might be linked to higher risk of type 2 diabetes and heart disease in adults.
In the diet-drink group, average blood sugar and total cholesterol edged up slightly, while the water group saw a slightly bigger drop in diastolic blood pressure.
There is context readers should know. The SWITCH trial was funded by the American Beverage Association, the industry group that represents makers of non-alcoholic drinks.
The authors state the funder had no role in designing the study, analyzing the data or interpreting the results.
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The authors also flagged two limits worth keeping in mind. Fewer than half of the people enrolled finished the full two years, and COVID-19 restrictions disrupted some of the assessments along the way.
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This article is made and published by Aksel Kryhlmand, who may have used AI in the preparation.