Human body composition as related to surface area.

There is a linear relationship between extracellular fluid and body surface area in man. During growth the body cell mass, fat-free solids, and body fat proportions of body weight increase while the extracellular fluid fraction decreases. Growth stops in men as soon as the body cell mass reaches 22.5 kg/m2 body surface area and in women when it reaches 16.9 kg/m5. The non-muscle cell mass and the muscle cell mass reach a 1:4 ratio in men whereas in women a 1:35 proportion--which is more favorable for pregnancy and lactation--is reached. The body composition of the newborn and the infant have fetal characteristics with a low body fat: surface area ratio and a low non-muscle cell mass: surface area ratio. The basal metabolic rate depends on the amount of non-muscle mass present, and the total energy change depends on body cell mass. This has been established by measurements of total body potassium, thiosulfate space, total body sodium, 24 h urine creatinine values and basal metabolic rate.