Determining adequate caloric intake to maintain body weight depends primarily on resting metabolic rate and activity level. Furthermore, energy cost also depends on the amount of lean body mass, intensity of exercise, and cardiorespiratory efficiency. Specifically, in two individuals with the same body weight, the individual with the greater proportion of lean body mass would possess a higher resting energy expenditure. Moreover, as intensity of exercise increases, energy cost does also. These factors must be considered before determining an appropriate caloric intake, training program, and macronutrient (carbohydrate, protein, and fat) ratio.

Ensuring proper nutrient intake should be reflected through optimal health and athletic performance, and maintenance of body mass and composition. An undesired gain or loss of body weight, adverse changes in body composition, or poor exercise or sports performance all indicate potentially inappropriate caloric intake.

Only rough estimates of daily caloric cost can be made because it is impractical for all athletes and fitness enthusiasts to use sophisticated methods of determining energy expenditure (i.e., activity monitors, calorimetry). Furthermore, daily energy requirements may vary depending on exercise intensity and other less understood factors, such as fluctuations in hormonal levels, especially in females. Regardless of the procedure used to determine daily energy expenditure, a consistent and reliable method for monitoring body weight and composition (accurately calibrated weigh scales, underwater weighing, skinfold calipers, ete.) should be used on a regular basis to assess the effects of a combined nutrition and training program. Thus, involuntary changes in weight andlor composition would signal the need for dietary alterations.

Determining resting energy expenditure (REE) can be ascertained from the equations listed in. Furthermore, because fat is considerably less metabolically active than muscle, individuals with greater lean body mass (all bodily constituents except fat) would possess relatively higher resting energy expenditures. This lower metabolism occurs primarily because women, in general, possess more body fat than do men of similar size. Consequently, as activity level and lean body mass (LBM) vary among individuals, total daily energy expenditure does as well.

For an average person, this sum comprises approximately 60-75% of the daily energy expenditure. The remaining energy consumption includes the thermic effect of food intake, which comprises approximately 5-10% of energy intake and the thermic effect of physical activity, which constitutes roughly 15-30%.1 Accordingly, the energy allowance for athletes may range between approximately 1.6 to 2.4 X REE.

Energy requirements vary extensively depending on the volume of daily activity, particularly among athletes. Economos et al. recommend, as a general guideline, that male athletes consume at least 50 kcal/kg/day and females consume approximately 45 to 50 kcal/kg/day when training for more than 90 minutes daily. Based on these estimates, a 50-kg (242-lb.) football player training for 1.5 hours daily would require over 5500 kcal daily, whereas a 50-kg female tennis player training for the same duration would require approximately 2350 kcal/day.

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