Randomized trial of carbonated water consumption on snacking behavior, alcohol intake, and health indices in healthy Japanese adults

Lifestyle-related diseases associated with obesity remain a major public health concern in Japan, in which eating and drinking habits play a critical role. Energy-free carbonated water has been suggested to promote sensations of fullness and may serve as a low-caloric alternative to caloric foods or alcoholic beverages; however, evidence regarding its sustained effects on habitual behaviors and objective health indices is limited. In this randomized, open-label, placebo-controlled, parallel-group trial, 46 healthy Japanese adults (aged 20-64 years; body mass index BMI, kg/m², 23.0-<30.0) were allocated to consume either carbonated water (4.3 ± 0.1 g carbon dioxide per 500 g/day) or non-carbonated water once daily for 12 weeks; 45 participants completed the study (carbonated, n = 22; placebo, n = 23). Changes from baseline in snacking frequency, alcohol intake, anthropometric measurements, and blood biochemical parameters were compared between groups. Compared with the placebo group, the carbonated water group showed a greater reduction in snacking frequency (times/week) at week 4 (mean difference - 1.39; 95% confidence interval CI - 2.82 to -0.28; P = 0.018) and week 12 (- 1.49; 95% CI - 2.93 to - 0.05; P = 0.049). Alcohol intake (g/week) was also reduced at week 12 (- 24.44; 95% CI - 44.02 to - 4.86; P = 0.019). At week 12, modest decreases were observed in body weight and body mass index (BMI) compared with placebo (body weight: -0.72 kg; 95% CI - 1.37 to - 0.07; P = 0.036; BMI: -0.26 kg/m²; 95% CI - 0.50 to - 0.02; P = 0.037). In addition, liver-related enzymes showed favorable changes at week 12, including lower aspartate aminotransferase (AST) (- 4.05 U/L; 95% CI - 7.57 to - 0.53; P = 0.034) and alanine aminotransferase (ALT) (- 9.47 U/L; 95% CI - 18.01 to - 0.93; P = 0.026). No study beverage-related adverse events were observed. These findings suggest that daily consumption of carbonated water may be associated with favorable changes in snacking and alcohol consumption behaviors and modest improvements in selected anthropometric and liver-related indices. Given the exploratory nature of the analyses and multiple outcomes without multiplicity adjustment, findings should be interpreted cautiously.