How drinking water before meals reduces caloric intake — and the age limit on that finding.
What the evidence says
- *The age boundary, stated first because it qualifies everything below: meal energy intake fell significantly with a water preload in older adults (60–80y: 682 → 624 kcal, P = 0.02) but not* in younger adults (21–35y: 892 vs 913 kcal, P = 0.65). The proposed reason is slower gastric emptying with age1
- Drinking 500 ml of water 30 minutes before breakfast reduced meal energy intake by ~13% (~74 kcal) in overweight and obese older adults — 500 kcal with preload vs 574 without, P = 0.004, in a within-subjects crossover2
- Over 12 weeks, pre-meal water drinkers on a hypocaloric diet lost ~2 kg more than those on the diet alone (n = 48, aged 55–75)3
- The water group showed a 44% greater rate of weight loss than the non-water group, with greater loss of total fat mass3
- Mechanism: water adds stomach volume, contributing to earlier fullness signals — a *volume* effect, not a correction of mistaken hunger2
- Simple, no-cost intervention requiring no willpower2,3