Two-Year Trial Finds Diet Drinks Match Water for Weight Loss

Key points

• 493 adults with overweight or obesity were randomly assigned to drink either water or diet beverages containing aspartame, acesulfame-K, or sucralose for 104 weeks.
• The diet group lost an average of 4.8 kg (10.6 lbs), while the water group lost 3.7 kg (8.2 lbs); the difference was not statistically significant.
• Both groups maintained weight loss during the final year without program support and showed improvements in waist/hip measurements and body composition.
• The study was funded by the American Beverage Association, though researchers stated they retained independent control over data analysis and reporting.
• Findings contradict World Health Organization advice against using non-sugar sweeteners for weight control, providing long-term clinical evidence previously lacking.

Background

This trial extends the earlier SWITCH trial published in 2023. It addresses ongoing debates about artificial sweeteners, particularly the 'cephalic phase insulin response' theory, which suggests sweeteners may trigger insulin spikes and increase hunger. Previous observational studies often linked diet drink consumption to obesity, but researchers note these may suffer from reverse causality, as overweight individuals are more likely to choose zero-calorie options.

How outlets are covering it

SciTechDaily and Click2Houston emphasize the equivalence of diet drinks and water for weight management, highlighting the lack of metabolic harm. ACSH notes that while the study is well-designed, it had high attrition (only 220 of 493 participants completed the unassisted phase) and was industry-funded, urging caution. USA Today acknowledges the weight-loss findings but points to other research linking artificial sweeteners to cognitive decline, liver disease, and dental erosion, suggesting diet drinks are not nutritionally identical to water.

Why it matters

The results provide long-term clinical evidence that may influence future World Health Organization guidelines and public health policies regarding the use of non-nutritive sweeteners. For individuals managing weight, the study suggests that replacing sugary beverages with diet versions is a viable strategy that does not negatively impact long-term weight maintenance or metabolic health.

What to watch

Researchers hope these findings will inform updated international health guidance. The study does not resolve all debates, as it did not measure insulin responses directly, and other health risks associated with artificial sweeteners remain under investigation in separate studies.