Relationship of Body Composition to Basal Metabolic Rate in Normal Man

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Abstract
Basal metabolic rates and estimates of the fluid compartments of the body were obtained on 17 healthy young men and analyzed by statistical methods. Data and analyses suggest the following conclusions. The commonly used relationship between basal metabolic rate and surface area is not a primary relationship, but depends upon an interrelationship of both these measurements to extracellular or interstitial fluid. A close and direct relationship exists between extracellular or intersitial fluid volume and basal metabolic rate that is relatively unaffected by body size or other composition. There is a constant correlation between intracellular fluid and basal metabolic rate which is unaffected by body size or other components of body composition. When total body water is held constant the relationship is inverse; higher metabolic rates are associated with lower intracellular fluid volumes. Intracellular fluid is not closely correlated with extracellular or interstitial fluid volume. The relationship of intracellular fluid volume to basal metabolic rate, and extracellular or interstitial fluid volume to basal metabolic rate are independent of one another. The total body water has inconstant proportions of plasma, interstitial and intracellular fluids. Any relationship between total body water and basal metabolic rate is, therefore, dependent upon a function of at least 2 of its parts, interstitial and intracellular fluid. While few of these correlations constitute unchanging indices, basal metabolic rate can be predicted from the volume of the body fluid compartments as well as, or better than, from the more commonly used standard of reference, surface area.