Effects of replacing diet beverages with water on weight loss and weight maintenance: 18-month follow-up, randomized clinical trial

Background: Beneficial effects of replacing diet beverages (DBs) with water on weight loss, during a 24-week hypoenergetic diet were previously observed. However, it is not known whether this difference is sustained during a subsequent 12-month weight maintenance period. Objective: To evaluate effects of replacing DBs with water on body weight maintenance over a 12-month period in participants who undertook a 6-month weight loss plan. Design: Seventy-one obese and overweight adult women (body mass index (BMI): 27–40 kg m –2 ; age: 18–50 years) who usually consumed DBs in their diet were randomly assigned to either substitute water for DBs (water group: 35) or continue drinking DBs five times per week (DBs group: 36) after their lunch for the 6-month weight loss intervention and subsequent 12-month weight maintenance program. Results: A total of 71 participants who were randomly assigned were included in the study by using an intention-to-treat analysis. Greater additional weight loss (mean±s.d.) in the water group was observed compared with the DBs group after the 12-month follow-up period (−1.7±2.8 vs −0.1±2.7 kg, P =0.001). BMI decreased more in the water group than in the DBs group (−0.7±1 vs −0.05±1.1 kg m – 2 , P =0.003). There was also a greater reduction in fasting insulin levels (−0.5±1.4 vs −0.02±1.5 mmol l –1 , P =0.023), better improvement in homeostasis model assessment of insulin resistance (−0.2±0.4 vs −0.1±0.3, P =0.013) and a greater decrease in 2-h postprandial plasma glucose (−0.2±0.3 vs −0.1±0.3 mmol l –1 , P <0.001) in the water group compared with the DBs over the 12-month weight maintenance period. Conclusions: Replacement of DBs with water after the main meal in women who were regular users of DBs may cause further weight reduction during a 12-month weight maintenance program. It may also offer benefits in carbohydrate metabolism including improvement of insulin resistance over the long-term weight maintenance period.