The aim of this study was to provide robust evidence on the long-term use of non-nutritive sweetened (NNS) beverages on weight management, by comparing NNS beverages and water during 1 year of assisted weight management followed by a voluntary, unassisted 1-year extension. In this parallel-group, open-label, controlled equivalence trial, 493 adults with BMI 27–35 kg/m2 who regularly consumed cold beverages were randomised 1:1 to water (n 246) or NNS beverages (n 247). Participants joined a group behavioural weight-management programme comprising assisted meetings weekly (12-week weight-loss phase) then monthly (40-week weight-maintenance phase), followed by unassisted monitoring for 52 weeks with a final meeting at week 104. The final 52-week unassisted phase was completed by 220 participants (water: n 117; NNS beverages: n 103), 27·7 % of whom were NNS beverage-naïve (naïve was defined as NNS beverages comprising ≤ 25 % of beverages in the 5 years before screening). In the unassisted monitoring phase, the primary endpoint was weight change from baseline at week 104 (equivalence: two-sided P > 0·05). Participants consuming water maintained a weight loss of 3·7 kg over 104 weeks, compared with 4·8 kg with NNS beverages; the between-group difference was not significant. After the final 52-week unassisted phase of the 104-week behavioural weight-management programme, water and NNS beverages showed equivalence regarding weight change from baseline. Our findings suggest people can lose weight and maintain it for 2 years, when drinking either NNS beverages or water and taking part in weight-management programmes.

This trial is registered with ClinicalTrials.gov: NCT02591134.