If you’ve been forcing down plain water to drop a few pounds when you really just want a Diet Coke (there’s nothing quite as refreshing as a mid-day ice-cold “fridge cig”), science has some potentially good news for you.
According to a University of Liverpool study published in the British Journal of Nutrition, diet drinks and water performed similarly for long-term weight management. But before we declare diet soda the “new water,” let’s look at the facts.
What Did the Study Find?
Researchers randomly assigned 493 adults with overweight or obesity to drink at least two daily servings of either water or non-nutritive sweetened drinks — like diet colas and sweetened flavored waters. Everyone also participated in a behavioral weight-management program, with weekly meetings initially, then monthly meetings through the first year. The second year was an optional extension without those sessions.
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Among the 220 participants who completed the two-year follow-up, water drinkers maintained an average weight loss of about 8.2 pounds, while the diet-drink group maintained about 10.6 pounds. The difference wasn’t statistically significant. Analyses estimating missing participants’ results also found no significant difference.
That’s encouraging, but it doesn’t mean either beverage caused the weight loss. These people were also participating in a program that included dietary advice and encouragement to increase physical activity.
Here’s Why I’m Skeptical
The study was funded by the American Beverage Association. (Something I’d like to know before celebrating the results.) The association also funded medical-writing assistance, and a representative had an opportunity to review the manuscript. The authors say the funder wasn’t involved in the trial’s design, conduct, analysis, or interpretation, and that final content decisions were theirs.
Industry funding doesn’t automatically make the finding wrong, but it deserves disclosure (which they provided), especially when the finding concerns the products the industry sells.
Then there’s the follow-up: 493 people started, but only 220 completed the two-year assessment. The researchers acknowledged that the low completion rate was a limitation.
So, Are Diet Drinks Healthy?
That’s a different question. This study suggests that diet drinks can fit into a weight-management program. It doesn’t establish that they’re as healthy as water or settle questions about long-term sweetener consumption.
Other research has also raised some concerns:
- Cognitive health: A September 2025 study published in Neurology found an association between consuming higher amounts of certain low- and no-calorie sweeteners across food and drinks and accelerated cognitive decline.
- Liver function: Research presented at a 2025 conference linked artificially sweetened drinks to an increased risk of metabolic dysfunction-associated steatotic liver disease, a condition involving fat buildup in the liver.
Both studies were observational, so neither proves that drinks or sweeteners caused those outcomes. That distinction matters here just as much as the funding disclosure does.
The takeaway? Similar weight-loss results aren’t a blanket health endorsement. Given the industry funding and how many people didn’t finish the study, I’m taking this one with a grain of salt.
