Core finding: The University of Liverpool ran the longest and most comprehensive randomised controlled trial on non-nutritive sweetened (NNS) soft drinks. Over 104 weeks, diet beverages were equivalent to water for long-term weight management. The results were published in the British Journal of Nutrition.
Study Design
- Name: SWITCH (effectS of non-nutritive sWeetened beverages on appetITe during aCtive weigHt loss).
- Participants: 493 adults with overweight or obesity.
- Intervention: Everyone followed a structured behavioural weight management programme. Participants were randomised to drink either water or commercially available diet beverages daily.
- Sweeteners tested: aspartame, acesulfame-K, and sucralose, at levels well within European Food Safety Authority (EFSA) safety thresholds.
- Follow-up: Two years, including a final year without active support.
- Continuation: It builds on earlier findings published in the International Journal of Obesity in 2023.
Researchers and Funding
- Led by Professor Jo Harrold (Dean of Psychology, University of Liverpool) and Professor Jason Halford (University of Leeds, formerly Liverpool).
- Funded by the American Beverage Association, though the team states it was independent of the funder and had full control over analysis and reporting. The work was peer-reviewed.
Key Results
- Equivalent weight loss at 104 weeks: −4.8 kg (NNS) vs −3.7 kg (water), a non-significant difference.
- Weight reduction was sustained over two years in both groups, even in the unassisted final year.
- Waist and hip circumference decreased, and body composition and several metabolic biomarkers improved in both groups.
- No clinically meaningful differences in blood pressure or cholesterol between the sweetener groups and water.
- Sugar intake fell in both groups, with slightly greater reductions in the NNS group.
Implications
- The results do not support concerns that NNS beverages disrupt appetite regulation or cause long-term metabolic harm.
- The findings directly address the WHO guidance advising against non-sugar sweeteners for weight control, which relied on uncertainty from observational studies. The authors say this long-duration randomised evidence can inform global guidelines.
- Harrold: concerns about sweeteners disrupting appetite or causing weight gain are not supported in a rigorous, long-term randomised trial; she hopes it informs WHO guidance and public health policy.
- Halford: the study provides long-term clinical evidence that was missing from international discussions, and NNS beverages offer an effective alternative to sugar-sweetened drinks for people managing their weight. (The text cuts off here.)
Points to Keep in Mind
- Industry funding: the trial was funded by the beverage industry. The authors state their independence, but this is worth weighing when interpreting the results.
- Scope: the results apply to adults with overweight or obesity in a structured weight-loss programme, and to three specific sweeteners in beverages, not necessarily to all sweeteners or the general population.
- Comparison: the finding is that diet drinks are equivalent to water, not superior. The weight difference favoured NNS numerically but was not statistically significant.
Overall Conclusion
For people trying to lose or maintain weight, diet drinks sweetened with aspartame, acesulfame-K, or sucralose performed as well as water over two years, with no evidence of harm to appetite, blood pressure, or cholesterol. This challenges the basis of the WHO’s cautious stance, though independent replication would strengthen the case.