Randomized trial shows diet drinks lead to greater weight loss in adults — Evidence Review

A large two-year randomized trial found that diet drinks were just as effective as water for maintaining weight loss in adults with overweight or obesity. Most related studies support the conclusion that both water and non-nutritive sweetened beverages can be effective alternatives to sugary drinks for weight management, though some research has suggested possible differences in long-term health outcomes.

• Several previous trials show that replacing sugar-sweetened beverages with either water or diet drinks leads to modest weight loss, with some evidence suggesting non-nutritive sweetened drinks may, in some contexts, be slightly more effective than water, but most studies find no meaningful difference 1 3 4.
• Meta-analyses consistently report that reducing sugar-sweetened beverages lowers body weight and that both water and diet drinks lead to better weight maintenance than continued sugary drink consumption 5 8 14.
• Some observational research has linked higher diet drink consumption with increased health risks, but these associations may be confounded by reverse causality and do not contradict evidence from randomized trials showing that, within weight management programs, diet drinks are not inferior to water for weight loss 11 13.

Study Overview and Key Findings

Efforts to reduce sugar-sweetened beverage consumption are central to public health strategies targeting obesity and related chronic diseases. However, debate persists about the best alternatives—particularly whether non-nutritive sweetened (diet) drinks are as effective and safe as water for long-term weight management. The new study led by the University of Liverpool addresses this gap using a rigorous, two-year randomized controlled design and extended follow-up, providing important evidence relevant to ongoing policy discussions and guidance from organizations such as the World Health Organization.

Property	Value
Study Year	2026
Organization	University of Liverpool, University of Leeds
Journal Name	British Journal of Nutrition
Authors	Joanne A. Harrold, Scott Hill, Cristina Radu, Paul Thomas, Paula Thorp, Charlotte A. Hardman, Paul Christiansen, Una Masic, Lauren McGale, Dan J. Cuthbertson, Jason C.G. Halford
Population	Adults with overweight or obesity
Sample Size	n=493
Methods	Randomized Controlled Trial (RCT)
Outcome	Weight loss, waist and hip measurements, metabolic health
Results	Weight loss averaged 4.8 kg in diet group and 3.7 kg in water group.

Literature Review: Related Studies

We searched the Consensus paper database, drawing on over 200 million research papers, to identify studies relevant to diet drinks, water, and weight loss. The following search queries were used:

1. diet drinks weight loss comparison
2. water intake weight reduction effects
3. long-term effects diet beverages health

The table below summarizes key topics and findings from the literature:

Topic	Key Findings
Do diet drinks and water have similar effects on weight loss and maintenance?	- Both non-nutritive sweetened beverages and water are effective alternatives to sugar-sweetened beverages for weight loss, with several RCTs finding no significant difference between them in structured programs 1 3 4. - Some studies suggest non-nutritive sweetened beverages may be slightly more effective than water for weight loss in the short term, but overall differences are small and not always statistically significant 3 4.
What are the long-term health effects of replacing sugary drinks with alternatives?	- Replacing sugar-sweetened beverages with either water or low-calorie/diet beverages leads to lower long-term weight gain and reduced risk of obesity 5 8 14. - Long-term observational studies suggest possible links between high consumption of diet drinks and increased risk of some cardiometabolic diseases, but these findings are complicated by confounding and reverse causality 11 13.
How do beverage choices affect appetite, energy intake, and metabolic outcomes?	- Most trials show that both water and diet beverages reduce total energy intake compared to sugary drinks, and neither disrupts appetite regulation or metabolic health markers in the context of weight management programs 1 3 7. - Drinking water before meals may help reduce acute energy intake, but evidence for a sustained effect on weight loss beyond structured dietary interventions is mixed 6 7 9.
Is there a best alternative to sugar-sweetened beverages for weight management?	- The evidence suggests that both water and non-nutritive sweetened beverages are preferable to sugar-sweetened drinks for weight loss and maintenance, but it remains unclear if one is superior; more research is needed to determine the optimal substitute 1 4 14. - Substituting water for sugary drinks is associated with modest but consistent benefits for weight control in diverse populations 8 9 14.

Do diet drinks and water have similar effects on weight loss and maintenance?

The new University of Liverpool study's finding—that diet beverages are as effective as water for long-term weight loss maintenance—aligns closely with several randomized controlled trials. These studies generally report that both water and non-nutritive sweetened drinks lead to comparable weight loss when replacing sugary beverages in the context of structured weight management programs. Some trials have found slightly greater short-term weight loss with diet drinks, but the difference typically does not persist or reach statistical significance over longer periods 1 3 4.

• Multiple RCTs have demonstrated that replacing caloric beverages with either water or diet drinks results in modest, sustained weight loss among adults with overweight or obesity 1 3 4.
• In one-year and 12-week trials, non-nutritive sweetened beverages sometimes produced greater weight loss than water, but the clinical significance of this difference is debated 3 4.
• The current study's two-year duration and follow-up after behavioral support ended strengthen the evidence that both approaches are effective for weight maintenance.
• No evidence from RCTs supports the idea that diet drinks hinder weight loss compared to water in these settings 1 3 4.

What are the long-term health effects of replacing sugary drinks with alternatives?

A large body of evidence from both intervention trials and prospective cohort studies finds that reducing sugar-sweetened beverage intake, regardless of whether the substitute is water or a diet drink, is associated with less weight gain and improved metabolic health. However, some observational studies report associations between high consumption of diet drinks and increased risks of obesity, diabetes, and cardiovascular disease. These findings may reflect confounding by indication (i.e., people at higher risk choosing diet drinks) rather than a causal effect 5 8 11 13 14.

• Meta-analyses confirm that both water and diet drinks are preferable to sugar-sweetened beverages for long-term weight management 5 8 14.
• Cohort studies sometimes observe links between high diet drink consumption and increased cardiometabolic risk, but RCTs do not support a harmful effect when diet drinks are used as part of a weight loss strategy 11 13.
• Policy recommendations universally emphasize reducing sugary drink consumption, with water as the first-line alternative and diet drinks as a practical secondary option 10 12 14.
• The new study adds robust randomized evidence that diet drinks do not undermine long-term weight loss or metabolic health within structured programs.

How do beverage choices affect appetite, energy intake, and metabolic outcomes?

Both water and non-nutritive sweetened beverages, when substituted for sugary drinks, reduce total caloric intake and support weight loss. Most studies find no evidence that non-nutritive sweeteners significantly disrupt appetite regulation or metabolic markers in adults, though the topic remains of interest in public health debates 1 3 6 7 9.

• Acute trials show water before meals can reduce energy intake, particularly in older adults, but the effect may diminish over time 6 7.
• Randomized trials in weight loss programs report no major differences in appetite or metabolic health outcomes between water and diet drink groups 1 3 9.
• Both strategies lead to decreases in waist circumference, blood pressure, and improvements in other health markers compared to sugary drinks 1 3 4.
• The current study did not observe adverse effects on appetite or metabolic health in the diet drink group during two years of follow-up.

Is there a best alternative to sugar-sweetened beverages for weight management?

While evidence supports both water and diet drinks as effective substitutes for sugary beverages, it remains unclear whether one is definitively superior for all individuals or in all settings. Some research suggests water may confer additional hydration benefits, while diet drinks may offer a more palatable transition for those seeking to reduce caloric intake without sacrificing sweetness 1 4 8 9 14.

• Both water and non-nutritive sweetened beverages lower energy intake and support weight loss versus sugar-sweetened drinks 1 4 8 14.
• The choice between water and diet drinks may depend on personal preference, prior consumption patterns, and individual health considerations 8 9 14.
• No long-term RCTs have established clear superiority of one alternative over the other for weight management.
• Further research is needed to clarify whether certain subgroups may benefit more from one substitute than the other 14.

Future Research Questions

Despite the strength of the new two-year trial, questions remain about the long-term health effects of non-nutritive sweetened beverages, potential differential impacts in various populations, and the best strategies for sustained weight maintenance. Future research should address these open questions to help refine dietary guidance and public health policy.

Research Question	Relevance
What are the long-term metabolic and cardiovascular effects of replacing sugar-sweetened beverages with diet drinks?	Observational studies suggest possible risks with high diet drink intake, but randomized evidence is limited and conflicting on long-term cardiometabolic safety 11 13. Further long-term trials are needed to clarify these effects in diverse populations.
Do non-nutritive sweeteners affect appetite, gut microbiota, or glucose metabolism over years?	While short-term studies find no significant disruption of appetite or metabolism, the potential for subtle long-term effects on physiology and gut health remains an open question 7 9. More mechanistic and long-duration studies are needed.
Are there specific subgroups for whom water is more effective than diet drinks for weight maintenance?	Most studies find no overall difference, but it is unclear if factors such as age, baseline diet, or metabolic health modify the comparative effectiveness of water versus diet drinks for sustained weight management 1 3 4.
What are the behavioral and psychological factors that influence beverage substitution choices in weight loss?	Adherence to beverage changes is critical for success, but little is known about the motivators and barriers to choosing water versus diet drinks as substitutes for sugary beverages in real-world settings 8 9 14.
How do water and diet drinks compare for weight loss in children and adolescents?	Most research to date focuses on adults; there is a need for randomized trials in younger populations to inform age-appropriate recommendations 5 8.