Zero-calorie drinks no worse than water for weight loss, 2-year trial finds

Many people trying to lose weight reach for zero-calorie beverages instead of sugary sodas, yet the World Health Organization advises against using non-nutritive sweeteners as a weight-management tool.

Now, a new study has found that overweight adults who drank zero-calorie beverages for two years as part of a weight-loss program lost and kept off roughly the same amount of weight as those who drank water.

Research on the relationship between zero-calorie drinks and body weight has long produced mixed results. Some observational studies have found that heavier consumers of such beverages tend to gain more weight, while clinical trials that switched participants from sugary drinks to zero-calorie alternatives have shown weight loss.

A research team led by Joanne Harrold of the University of Liverpool and Jason Halford of the University of Leeds published their findings in volume 136 of the British Journal of Nutrition, comparing weight changes in overweight and obese adults assigned to drink either zero-calorie beverages or water over two years.

The research team divided 493 overweight or obese adults into two equal groups. One group drank at least two bottles of zero-calorie beverages a day, while the other cut out sweeteners entirely and drank only water. Both groups took part in a dietitian-led weight-loss program for one year, then managed their weight independently for a second year.

Among the 220 participants who completed the full two-year program, the water group lost an average of 3.7 kilograms and the zero-calorie beverage group lost 4.8 kilograms — a difference the researchers deemed equivalent. Waist circumference also shrank by similar margins: 4.5 centimeters in the water group and 5.5 centimeters in the zero-calorie group.

About one in four participants had rarely consumed zero-calorie drinks before the study, yet prior consumption habits made no difference to weight-loss outcomes.

Both groups shed the most weight in the first 12 weeks and reached their lowest weight before the one-year mark, after which they gradually regained some. The rate of regain was slightly slower in the zero-calorie beverage group.

"Participation in a weight-management program can lead to weight loss and maintenance whether you drink zero-calorie beverages or water," the researchers wrote.

A common concern about zero-calorie drinks is that tasting sweetness without receiving calories confuses the body, triggering hunger and ultimately leading to greater food intake. In this study, the zero-calorie beverage group reported a slight increase in hunger over the two years, but the difference from the water group was not statistically significant.

Blood pressure and blood sugar improved somewhat more in the water group. Diastolic blood pressure fell by 4.5 mmHg in the water group compared with 1.7 mmHg in the zero-calorie beverage group. Glycated hemoglobin — a measure of average blood sugar over the preceding three months — declined slightly in the water group but edged up slightly in the zero-calorie beverage group.

The researchers said the differences between the two groups were not large enough to be clinically meaningful.

The study was funded by the American Beverage Association, an industry group whose members include Coca-Cola and other drink companies, which also supplied the beverages used in the trial. The research team said the association had no involvement in the study's design, analysis or interpretation.

All participants were enrolled in a weight-loss program. The researchers noted several limitations: the study did not compare zero-calorie drinks against sugary beverages, and it did not assess the long-term safety of non-nutritive sweeteners.

DOI: 10.1017/S0007114526108150

Harrold JA, Hill S, Radu C, et al. Effect of non-nutritive sweetened beverages v. water on body weight: long-term results of a randomised controlled trial. British Journal of Nutrition. 2026;136(4):482-493.