The study enrolled healthy Caucasian French men and women, aged 25–40 years, with a BMI between 18·5 and 29·5 kg/m2 and with habitual fluid consumption (drinking-water plus other beverages) falling into either the bottom or top thirds of the French fluid intake distribution. Initial inclusion criteria included the ability to stay at home, abstain from strenuous physical activity for the study duration (4 d), access the Internet and live within a maximum of 30 min from the investigating centre. Exclusion criteria included use of medication likely to interfere with metabolism, such as hypotensive or diuretic treatment, history of gastrointestinal or metabolic disease (such as diabetes mellitus); renal, hepatic or cardiac failure, smoking more than fifteen cigarettes per d; or consumption of more than two (women) or more than three (men) standard servings of alcohol per weekday (where one standard serving represents 250 ml beer, 100 ml wine or 30 ml of spirits). Participants completed a total of six clinic visits (Fig. 1 ). After an initial eligibility screening (V0), potentially eligible subjects completed a clinical examination and received instructions on to use an electronic diary questionnaire (e-diary; MXS-Epidemio), described in detail below, to estimate usual fluid consumption over three consecutive weekdays. Subjects then returned to the clinic for an inclusion visit (V1), where their e-diary was used to identify individuals whose daily fluid consumption was consistent with either the low drinker (LD; ≤ 1·2 litres/d per 1·73 m2 of body surface area) or high drinker (HD; 2·0–4·0 litres/d per 1·73 m2 body surface area) groups.![]()
Schematic of subject recruitment, group allocation and experimental phase. 24hU, 24 h urine; LD, low drinker; HD, high drinker; FMU, first morning urine.
