Diet Soda Rivals Water for Weight Loss, Study Finds

A two-year study from the University of Liverpool has upended a common assumption about weight loss: that diet soda is inherently worse than water. Researchers tracked 493 adults between 18 and 65 years old, all carrying extra weight, and split them into two groups. One group drank 22.3 ounces of water daily. The other drank the same volume of diet beverages—sodas, low-calorie fruit drinks, and flavored waters sweetened with aspartame, acesulfame potassium, or sucralose. Over 104 weeks, the diet drink group shed about 10.6 pounds on average, while the water group lost 8.2 pounds. The difference was small enough that researchers found no meaningful distinction between them.

Both groups also saw similar improvements in waist and hip measurements, body fat percentage, and cholesterol levels. The findings, published in the British Journal of Nutrition, suggest that the artificial sweeteners themselves did not sabotage weight loss the way some health advocates have long claimed. But there is an important caveat buried in the methodology: neither group was simply drinking beverages and hoping for results. Both participated in a structured weight-management program that included nutrition counseling, behavioral coaching, and exercise recommendations. The beverages were part of a larger intervention, not the driver of it.

Alix Turoff, a registered dietitian in New York City who reviewed the study, emphasized this distinction. The weight loss did not come from diet soda's supposed metabolic magic. It came from the comprehensive program. The real value of diet beverages, she explained, is substitution—if someone normally consumes 250 calories in regular soda and switches to zero-calorie alternatives, they are simply removing those calories from their day. The study also found no significant difference between groups in reported hunger or sugar cravings by the end of the trial, which matters because one persistent concern about artificial sweeteners is that they might trigger compensatory eating or increase appetite.

Turoff stopped short of declaring diet soda and water nutritionally equivalent. She still recommends water as the primary hydration choice. But she pushed back against the fear that diet drinks will automatically derail weight loss or cause weight gain. The evidence from this trial does not support that worry. The study design itself was revealing: researchers compared diet beverages to water rather than to regular soda, which meant they were testing whether the sugar substitutes hindered weight loss, not whether they helped it. On that specific question, the answer was no.

The research does carry limitations worth naming. It took place at a single location in England, which narrows its applicability. The researchers did not collect data on race or ethnicity, a gap that further limits how broadly the findings can be generalized. Of the 493 participants who started the study, only 220 completed the full 104-week assessment—a 45 percent completion rate. The second year was voluntary, meaning those who stayed may have been more motivated or more disciplined than the broader population. The American Beverage Association funded the trial, though the authors stated the association had no role in study design, data analysis, or interpretation. That funding source raises a natural question about whose interests shaped the research, even if the methodology itself appears sound.