Diet soda vs water: Study reveals which beverage is better for weight loss

Diet drinks containing sugar substitutes were found to be as effective as water for supporting weight loss in overweight or obese adults, according to a two-year randomized trial.

The study, led by the University of Liverpool, England, included 493 participants ranging from 18 to 65 years old, all of whom had a body mass index (BMI) between 27 and 35 (overweight or obese).

Half of them received 22.3 ounces of water each day, and the other half received the same amount of soda with non-nutritive sweeteners (about two cans) for a 104-week period.

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The group assigned to NNS drinks could choose from a variety of diet sodas, low-calorie fruit drinks and flavored waters. The primary sweeteners used were aspartame, acesulfame potassium and sucralose.

After two years, people drinking diet beverages had lost about 10.6 pounds, while those drinking water lost about 8.2 pounds.

People in both groups kept off a meaningful amount of weight for two years, even during the last year when they no longer had regular weight-management support, the researchers stated.

Both groups lost inches around their waists and hips and reduced body fat, but there was no meaningful difference between people drinking diet beverages and those drinking water.

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Additionally, total cholesterol remained within the healthy range in both groups.

The findings were published in the British Journal of Nutrition.

"The study does not show that diet beverages themselves caused the weight loss," Alix Turoff, a registered dietitian in New York City, told Fox News Digital.

"Everyone in the study was participating in a structured weight-management program that included nutrition counseling, behavioral support and physical activity recommendations."

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Turoff, who was not involved in the study, noted that the main value of including diet beverages comes down to substitution, "not that these beverages have a magical metabolic effect."

Notably, the study compared diet beverages with water — rather than with sugar-sweetened drinks — making it a test of whether the sugar substitutes themselves appeared to hinder weight loss efforts.

"If someone normally drinks 250 calories of regular soda and switches to zero-calorie soda, then they’re saving calories," she added.

The dietitian emphasized that these findings don’t mean 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," Turoff 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."

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There were some limitations with the research, including that it was conducted at one location in England. Race and ethnicity data were not collected, which limits the generalizability of the findings.

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Only 220 of the 493 participants who started treatment completed the 104-week assessment. The second-year extension was also voluntary, meaning those who continued may have been more motivated or more likely to stick with the program, Turoff noted.

While the trial was funded by the American Beverage Association, the study authors stated that the association did not participate in the study design, data analysis or interpretation of the results.