Effects of extreme environments on food intake in human subjects

Effects of extreme environments on food intake in human subjects are analys ed as behavioural and physiological adaptations to annual and circadian rhy thms, temperature and altitude. Effects of the environment on food intake t hrough food availability have direct consequences on energy balance and bod y weight. Different geographical regions show variations in the composition of dietary foods, i.e. the relative proportions of carbohydrate, protein a nd fat. In developing countries the annual cycle appears to affect body wei ght through dependence on food availability. In West-European countries thi s effect appears to depend on physical activity. Energy and macronutrient i ntakes appear to follow a circadian pattern, with breakfast being relativel y high in carbohydrate and dinner being relatively high in fat. In cold con ditions, maintaining an adequate food intake is important in sustaining nor mal physiological responses to cold. Evidence for a possible cold-induced i ncrease in appetite is poor. A condition influencing level of intake is the palatability of the food. High altitude, i.e. hypobaric hypoxia, appears t o reduce appetite, energy intake and body mass, irrespective of acute mount ain sickness (AMS). Meal size is reduced and meal frequency increased. Unde r circumstances of AMS, dissociation between appetite and hunger occurs. Th us, spontaneous adaptation to extreme environments requiring increased ener gy intake occurs first by adaptation of body weight to a new energy balance . In general, prevention of a negative energy balance occurs by learning wi th respect to food intake. After return to normal, adjustment of energy int ake to the original energy balance occurs with restoration of body weight.