The results also undercut a persistent worry: that sweeteners disrupt appetite regulation or cause long-term metabolic harm. Tested rigorously over two years, those concerns did not materialize.

Why this matters for global guidance

The findings speak directly to recent World Health Organization guidance. The WHO advised against using non-sugar sweeteners for weight control, citing uncertainty in observational studies — research that tracks people's habits without controlling them. Observational studies can miss confounding factors; randomized controlled trials like SWITCH, which assign interventions by chance, carry stronger evidentiary weight.

Jo Harrold, dean of psychology at the University of Liverpool and lead researcher on the study, framed the results in that policy context. "These latest findings show that concerns about sweeteners disrupting appetite or causing weight gain are not supported when tested in a rigorous, long-term randomized trial," she said. "We hope this evidence informs future WHO guidance and public health policy."

Jason Halford, a professor of biological psychology and health behaviors at the University of Leeds who previously worked at the University of Liverpool, co-led the research. "This study provides the long-term clinical evidence that has been missing from international discussions," he said. "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."

The trial's full name reflects its design: the effectS of non-nutritive sWeetened beverages on appetITe during aCtive weigHt loss. The researchers conceived it to reduce sugar in the diet and to answer open questions about how sweeteners affect appetite when they replace sugar. The current work builds on earlier evidence the team published in the International Journal of Obesity in 2023.

Caveats to keep in mind

The American Beverage Association funded the study. The researchers say they operated independently of the funder and retained full control over the analysis and reporting of the findings. The trial also focused on adults with overweight or obesity in a structured weight management program, so the results may not translate directly to other populations or to everyday use outside such a program.

Still, for the millions of people weighing whether to reach for a diet soda or a glass of water, the evidence now says: over two years, either choice supports weight management equally well.