Patterns of human drinking: effects of exercise, water temperature, and food consumption

The effects of exercise, water temperature, and food consumption on patterns of ad libitum drinking were studied in 33 men during 6 consecutive cycles of 30 min walking (4.8 km.h-1, 5% grade) and 30 min rest in a climatic chamber (40 degrees C, 40% relative humidity). On two nonconsecutive days, subjects consumed 15 degrees C (cool) water during one trial and 40 degrees C (warm) water during the other. We previously reported that two groups of drinkers can be identified during work in the heat by the criterion of body weight (BW) loss during the trial. Thus, avid drinkers (D) drank sufficiently such that they lost less than 2% of their initial BW when consuming cool water and libitum, while reluctant drinkers (RD) lost more than 2% of their BW. When warm water was provided, fluid consumption was reduced by 29% and 54% in D and RD, respectively and BW deficits were comparably increased. Intake of cool water elicited cyclic drinking patterns with higher rates during walking than during rest periods in both D and RD, whereas consumption of warm water produced this cyclic pattern only after food ingestion during the third rest. Food consumption stimulated fluid intake and reduced BW losses in both trials. Compared to pre-prandial (hours 1-2.5) rates, average post-lunch drinking rates during the last 3 h increased 14% in D and 19% in RD when consuming cool water, and by 46% and 74%, respectively, with warm water. While food consumption has been encouraged to replace electrolytes lost in sweat when working in hot climates, our results indicate that food ingestion also enhances fluid consumption.