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FLUID REPLACEMENT AND HEAT STRESS
intakes and activity levels. Daily urinary outputs ranged from 0.5 to 4.4 liters/man/day, insensible water loss increased by 50%, from 0.8 to 1.2 kg/man/day, and total body water decreased from 44.4 to 41.6 liters. In general, people going to increased altitudes incur negative water balances (Consolazio et al., 1968). Studies of mountain climbers are contaminated with the concomitant fluid perturbations caused by cold exposure, by physical exercise, and usually by inadequate food intake. The negative fluid balance of mountain climbers is often very great, and large body weight and fluid losses (to 9.6 kg) have been reported (Nevison et al., 1962). Most investigators have reported hypovolemia of 6% - 21% during 2-3-week exposures to 2,000-4,500 m altitudes (Alexander et al., 1967; Dill et al., 1974; Krzywicki et al., 1971; Surks et al., 1966), with a 29% decrease observed after 18 weeks at 5,790 m altitude (Pugh, 1962). On the other hand, Krzywicki et al. (1971) found in well-fed men a small increase in extracellular fluid volume of 1.3 liters after they spent 6 days at 4,300 m. Also, Greenleaf et al. (1978) observed no significant change in plasma volume or fluid balance during 8 days at 2,287 m in well-fed and well-hydrated men. Thus, hypovolemia and hypohydration observed at high altitudes appear to be related to involuntary dehydration and to food deficits (anorexia).
Consumption of Food
Intakes of food and water are closely related (Johnson, 1964a); food intake is reduced during water deprivation, and water intake is reduced during starvation (Andersson and Larsson, 1961). Subjects undergoing acute starvation for 10 days with water, tea, and coffee given ad libitum exhibit an immediate increased loss of water by the kidneys followed by a lessening of the diuresis (Consolazio et al., 1967). The fluid intake declined progressively as starvation continued, and water balance was achieved on day 9 when the fluid intake and output were the same. Fluid intake increased greatly when food was eaten during the recovery period. Thus, food has a water-retaining effect.
FACTORS AFFECTING REHYDRATION BEVERAGE COMPOSITION AND SELECTION
Starkenstein (1927) conducted the first comprehensive laboratory study of the thirst-quenching properties of various concentrations of carbonic acid