The energy requirement for growth: An application of atkinson’s metabolic price system

Abstract

Atkinson’s metabolic price system has been applied to the calculation of the energy costs of growth of a 3-week-old, 3,900-g “male reference baby,” growing along the 50th percentile. The increase in weight of liver, brain, lung, spleen, and kidney has been calculated from literature data. The other organs and tissues were assumed to grow proportionally to the gain in body weight corrected for the weight gain of the organs mentioned above. The gross chemical composition of tissues and organs has been used to calculate the increases in specific tissue components, such as proteins, triglycerides, phospholipids, choiesterol, glycogen, DNA, and RNA. Of the total weight gain of 6.9 g/kg body wt/24 hr, 25.2% could be accounted for as solids deposited in the body, the remainder, 74.8%, being water. The energy needed to synthesize these solids has been calculated in terms of ATP equivalents, ATP being the form of energy used in the biochemical synthetic reactions. A total of 0.0614 mol ATP Eq is needed/kg body wt/24 hr in addition to 0.164 g glucose/kg body wt/24 hr. Proteins, which accumulate at a rate of 0.971 g/kg body wt/24 hr, take 87.7% of these ATP Eq. The energy needs for the active uptake of ions has also been calculated and was found to be 0.0108 mol ATP Eq/kg body wt/24 hr, which increases the total to 0.0722 mol ATP Eq kg body wt/24 hr. These ATP equivalents can be generated by the complete oxidation of 0.342 g glucose, which sets the total energy need to maintain growth at 0.506 g glucose/kg body wt/24 hr. Assuming an intake of humanized milk containing 69 kcal/100 ml, at 140 ml/kg body wt/24 hr, 2.2% of the total caloric intake is needed to cover the energy cost of normal growth. The metabolic price system theory as developed by Atkinson may prove to be very useful in calculating the energy requirements for specific functions, such as performance of mechanical work, maintenance of ionic equilibrium, and energy costs for replacing body constituents, as more becomes known about the stoichiometry of biochemical reactions in various organs. © 1975 International Pediatric Research Foundation, Inc.