. "15. Food Intake, Appetite, and Work in Hot Environments." Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press, 1993.
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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations
be more a result of external ambient temperature than of localized temperature changes and may be due to the rate of heat flow from the core to the periphery or vice versa, as no single temperature appears to uniquely govern the level of food intake (Spector et al., 1968).
Osmotic factors have also been shown to affect food intake in animals. Ingestion or intubation of hypertonic saline or glucose solutions results in decreased food intake in rats (Ehman et al., 1972; Kozub, 1972). However, intravenous administration of hypertonic infusions resulted in decreased food intake in rats only when the hyperosmolar solution was sodium chloride, but did not affect food intake when the solution was glucose or xylose (Yin and Tsai, 1973). As reviewed by Thompson (1980), this observed decrease in food intake serves as a protective mechanism that is demonstrated under conditions of total water deprivation, which significantly reduces food intake in most species studied, including pigeons (Ziegler et al., 1972). Ad lib food intake dropped to half in rats during a 24-hour period without water (Cizek and Nocenti, 1965), thus demonstrating that food intake and fluid balance are directly related. It appears that observations of decreased food intake in unacclimatized people in tropical climates may, to a large extent, be mediated by hypertonicity associated with initial dehydration, and improve as acclimatization occurs (Bass et al., 1955).
Not only is the stress of a hot environment due to thermoregulation and maintenance hydration, but it may be due to psychic stress as well. Such stress may be initiated by the degree of mental discomfort caused by the heat. Thus the impact of the need to (a) physiologically maintain thermoneutrality, (b) maintain normal hydration in spite of profuse sweating, and (c) feel comfortable in the heat may each affect the individual's appetitie and his/her perceived hunger to a different degree. Researchers cannot distinguish the difference between appetite and hunger in animals due to the lack of methods to communicate feelings; in humans, such information may be important in determining appropriate mechanisms for maintaining body weight and health status in prolonged exposure to heat. If an additional stress due to the situation occurs, such as that resulting from fear of death (as found in war or military conflict), then there may be additive effects on the desire to eat (appetite) or the perceived need to eat (hunger).
OBSERVATIONAL DATA ON INTAKE
A few studies (conducted primarily in foreign countries) do exist in which food intake of adults in hot and/or humid environments has been studied in isolated work environments. Edholm and Goldsmith (1966) reported their study in Bahrain and in the United Kingdom in which two groups of military men were followed in a carefully controlled environment. One group had spent a year in Bahrain prior to the experiment, while