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 age[1]
- The paper says so itself, and may be quoted for it: ”our findings should not be extrapolated beyond the age ranges studied”. Its completed sample was ~29 young and ~26 older adults from 40 and 34 enrolled, in a single acute test meal, and the authors call the sample “relatively small”[1]
- 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 crossover[2]
- 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 mass[3]
- Mechanism: water adds stomach volume, contributing to earlier fullness signals — a volume effect, not a correction of mistaken hunger[2]
- Increasing water consumption is ”a simple, inexpensive behavioral change which can be recommended as a component of a hypocaloric diet to possibly enhance weight loss outcomes” (corrected 2026-09-10 from ”Simple, no-cost intervention requiring no willpower”: no-cost and requiring no willpower are in neither `cwa02` nor `cwa03`, and the sentence is `cwa02`’s alone)[3]