Food intake in the real world: implications for nutrition and aging

Nutrient intakes are affected by two classes of factors, physiological and environmental. In the real world, environmental variables such as social factors, palatability, and the time of eating appear to have large influences on amounts ingested in the short-term. Physiological control mechanisms also operate to regulate intake, and they induce compensatory responses to deviations from the norm. These physiological influences only appear to have weak influences on short-term intake unless there are large deviations from the normal state, but over the long-term they act patiently and persistently to rectify the excesses produced by environmental fluctuations and thereby tend to maintain a relative balance between energy intake and expenditure. As individuals age there is a progressive decline in physiological function including the mechanisms that act to control intake in the young. This should not produce a problem in a healthy individual in a stable environment: however, if that situation should change due to illness or an environmental change such as the death of a spouse, which produces decline in intake, elderly individuals would not have the physiological mechanisms present to compensate. Thus, the deficit in energy intake would not be replaced, and the lower level of intake would be maintained as long as the new health condition or environment remains stable. Hence, the decline in the effectiveness of the physiological systems with age makes the elderly particularly vulnerable and unable to rebound from deficits. Although the elderly have difficulty compensating for deficits automatically by physiologically-induced adjustments, the studies of real world intake reviewed in this article suggest that compensation can be produced by adjustments to the environment. The elderly appear to be as responsive to environmental factors as younger individuals. In particular, they appear to increase intake in response to social facilitation, diurnal rhythms, the eating environment, and palatability to the same extent as their juniors. These data suggest that alterations in the social, temporal, environmental, or hedonic conditions of eating could induce desired alterations in the nutrient intakes of the elderly. The study of real world eating behavior has produced evidence that suggests that this strategy can work. It remains for future applied investigations to ascertain whether or not this strategy is effective in treating undernutrition in the elderly.