A desirable body weight depends on balancing energy intake – determined by food choices – with energy output – determined by one’s basal metabolism (energy needs of the body at rest) plus one’s level of physical activity. The number of calories an individual will need every day depends on age, sex, size, and level of physical activity.
The energy allowances, or recommended calorie intakes for men and women take these factors into account to establish a level “consonant with good health of average persons in each age group within a given activity.” (Pregnant and breast-feeding women, however, have greater needs, approximately 300 and 500 additional calories per day respectively, especially if the woman is also an adolescent and must satisfy her own growth requirements as well as those of the fetus.) In setting the RDA for energy, the pervasive problem of overweight in the United States was taken into account, and the following recommendations were made.
We should not only stay within optimum calorie levels to maintain ideal body weight, but if we are cutting down on calories, we should also select foods of greater nutrient density (most nutrients per calorie). The way to control body weight is by balancing food intake against physical activity. This is especially important for children, whose weight problems may set a pattern for life, and for the elderly, whose low energy needs may lead to a diet deficient in many of the nutrients needed for good health if nutrient-dense foods are not adequately used.