Key Takeaway:
- Similar weight loss in Diet Soda vs. Water: Diet soda drinkers lost about 4.8 kg over two years, compared with 3.7 kg for water drinkers, with no statistically significant difference.
- Diet drinks can replace sugary beverages: Low- or no-calorie drinks may help reduce sugar intake without undermining weight management.
- Water remains a healthy choice: The study does not prove diet soda is superior to water or establish all its long-term health effects.
Adults with overweight or obesity lost similar amounts of weight when they drank diet beverages or water over two years, according to a University of Liverpool trial published in the British Journal of Nutrition.
Researchers Track Weight Loss Over Two Years
The randomized controlled trial followed 493 adults with overweight or obesity who participated in a structured behavioral weight management program. Researchers assigned participants to drink either water or commercially available diet beverages sweetened with aspartame, acesulfame potassium, or sucralose.
After 104 weeks, participants drinking diet beverages lost an average of 4.8 kilograms (10.6 pounds), compared with 3.7 kilograms (8.2 pounds) among water drinkers. Researchers found the difference was not statistically significant, indicating neither beverage offered a clear advantage for long-term weight management.
The study, known as the SWITCH trial, examined whether non-nutritive sweetened beverages affected appetite regulation, weight loss, and weight maintenance. The first year included structured behavioral support, while the second year allowed researchers to assess whether participants maintained their progress without the same level of assistance.
Both groups experienced reductions in waist and hip measurements, improvements in body composition, and changes in several metabolic health indicators. Blood pressure and cholesterol outcomes were also similar between the groups.
Diet Drinks Help Reduce Sugar Consumption
The findings suggest diet beverages may offer an alternative for people who want to reduce their consumption of sugar-sweetened drinks without undermining weight management efforts. Both groups reduced their sugar intake, although the decline was slightly greater among participants who consumed diet beverages.
Professor Joanne Harrold, dean of psychology at the University of Liverpool and a researcher involved in the trial, said the findings challenge concerns that artificial sweeteners necessarily disrupt appetite or cause weight gain.
“These latest findings show that concerns about sweeteners disrupting appetite or causing weight gain are not supported when tested in a rigorous, long-term randomised trial,” Harrold said in a university statement.
Professor Jason Halford of the University of Leeds, who also worked on the research, said the results provide longer-term clinical evidence for discussions about low- and no-calorie sweetened drinks.
“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,” Halford said.
The researchers said the results could inform future public health discussions about sweeteners and weight management. The Diet Soda vs Water study addresses concerns about their effects on appetite and weight, although it does not resolve every question about the long-term health effects of artificial sweeteners.
Study Limitations Leave Questions Unanswered
The study received funding from the American Beverage Association, an industry group representing beverage companies. The University of Liverpool said the research team operated independently of the funder and retained control over the analysis and reporting of the findings.
The trial also focused on adults with overweight or obesity participating in a structured weight management program. Its results may not apply equally to people outside such programs or to those with different health needs and drinking habits.
Researchers examined weight, body measurements, and selected metabolic indicators, but the trial was not designed to establish every possible long-term effect of diet beverage consumption. Further research may help clarify how these drinks relate to other health outcomes over longer periods.
The findings do not suggest that people need to replace water with diet soda. Water remains a straightforward hydration choice, while diet beverages may help people reduce added sugar when substituted for sugary drinks.
For people managing their weight, the Diet Soda vs Water results emphasize that beverage choice is one part of a broader approach that includes eating habits, physical activity, and sustained behavioral changes.
