Metabolic Cost of Growth in Very Low-Birth-Weight Infants

Abstract

Summary: Forty-eight measurements of energy expenditure were performed in 15 very low-birth-weight infants during the first 6 wk of life. Their mean birth weight and gestation age was 1223 g and 31 wk respectively. Their mean weight gain was 11.2 g/kg · d (range: −6.6 to + 15.9 g/kg · d.). The mean energy expenditure increased from 170 kJ/kg · d (wk 1) to 252 kJ/kg · d (wk 6). There was a significant relationship between weight gain and energy expenditure (r = 0.58, P < 0.001) and also between the net increase in body weight gain and the net increase in energy expenditure (r = 0.80, P < 0.001). From the slopes of these regression lines, the metabolic cost of growth was found to be approximately 2.3 kJ/g of weight gain. Carbohydrate oxidation represented 80% of energy expenditure at the second wk and decreased to 65% the 6th wk, whereas lipid oxidation during the same period increased from 14 to 30% and the relative protein oxidation remained unchanged, covering 5–6% of the energy expended. Speculation: There is need for information on the metabolic cost of growth in very low-birth-weight infants because a significant proportion of energy expenditure is associated with the metabolic cost of growth due to tissue synthesis. An attempt has been made to investigate the relationship between weight gain and energy expenditure in very low-birth-weight infants. In addition, substrate oxidation was determined during the first wk of life in order to elucidate which fuel was oxidized during this period of rapid growth.