Abstract
1. Fluid intake, urine output and evaporative water loss were measured and fluid balance calculated in sixteen subjects for 1 d before Ramadan, during weeks 1–5 of fasting and on the 10th day after the end of Ramadan.
2. Plasma osmolality at 06.00 hours, the beginning of the fast, at 18.00 hours, before breaking the fast and at 19.00 hours, 1 h after breaking the fast, and urine osmolality during the day and night were measured before, during and after Ramadan.
3. All subjects developed an initial negative fluid balance which was maximum at the beginning of week 3 of fasting and that deficit was compensated for during the later weeks.
4. Compensation was brought about by an increase in urine concentration, a decrease in urine volume by day, and salt retention.
5. No significant changes were observed in plasma osmolality during the days of fasting and the ‘setting’ of plasma osmolality during Ramadan also was not changed.
6. It was concluded that healthy young adults maintain good control of fluid and electroytes during Ramadan.