Study details

For the study, researchers in England observed 493 adults that were overweight or obese over the course of 104 weeks. These adults participated in a structured behavioral weight management program and were randomly assigned to either drink water or commercially available diet beverages each day.

Those in the diet beverage group could drink diet sodas, diet carbonated soft drinks, diet fruit drinks, and diet fruit-flavored sweetened waters. They could also consume water but were required to consume at least two 33-milliliter servings of the eligible diet drinks per day.

Meanwhile, those in the water-only group were asked to abstain entirely from any of the listed diet beverages.

At the end of the study, the researchers found that people who drank diet beverages lost around 10.6 pounds while those who drank water lost around 8.2 pounds. People in both groups kept off a meaningful amount of weight for two years, even during the final year of the study when they no longer had regular weight-management support.

In addition, the researchers found that participants in both groups had reductions in waist and hip circumference alongside improvements in body composition and several metabolic biomarkers. Both groups also saw their sugar intake fall, with slightly larger reductions among those in the diet beverage group.

There were no meaningful differences in measures like blood pressure and cholesterol linked to long-term consumption of any of the non-nutritive sweeteners compared to water.

Discussion

The potential harms and benefits of diet beverages have long been studied. For example, previous research has found an association between diet soda consumption and weight gain, increased insulin, and blood glucose levels.

Other research has found an association between consuming higher amounts of low- and no-calorie sweeteners and accelerated cognitive decline. Meanwhile, a 2025 study found that even moderate amounts of artificially sweetened and sugary drinks were associated with an increased risk of liver disease.

Jason Halford, a professor of biological psychology & health behaviors at the University of Leeds and co-author on the study, said the research "provides the long-term clinical evidence that has been missing from international discussions. For people trying to manage their weight, non-nutritive sweetened beverages offer an effective alternative to sugar-sweetened drinks — and perform equivalently to water over two years."

Separately, Alix Turoff, a registered dietitian, noted that the study doesn't show a causal relationship between diet beverages and weight loss.

"Everyone in the study was participating in a structured weight-management program that included nutrition counseling, behavioral support, and physical activity recommendations," Turoff said, adding that the main value of including diet beverages comes down to substitution, "not that these beverages have a magical metabolic effect."

Turoff also emphasized the study's findings don't mean that water and diet soda are nutritionally identical.

"The study did not find significant between-group differences in hunger or sugar intake at the end of the trial, which is relevant because one common concern is that artificial sweeteners may increase appetite or lead to compensatory eating," she said. "I would still recommend water as the primary hydration choice, but I don't think people need to be afraid of diet drinks because they think they will automatically prevent fat loss or cause weight gain."