Growth is a sensitive indicator of whether an infant’s energy requirements are satisfied. Energy demands for growth constitute about 35 percent of the total energy requirement during the first three months of life (40 percent in the first month), this proportion is halved in the next three months (i.e. to about 17.5 percent), and further reduced to one-third of that during the ensuing six months (i.e. to less than 6 percent) and to only 3 percent at 12 months. Energy for growth falls to less than 2 percent of daily requirements in the second year, remains between 1 and 2 percent until mid-adolescence, and gradually disappears by 20 years of age.
Energy needs for growth have two components: 1) the energy used to synthesize growing tissues, which is part of the total energy expenditure measured with DLW; and 2) the energy deposited in those tissues, basically as fat and protein, because carbohydrate content is insignificant. Hence, energy requirements in infancy can be calculated by adding the energy deposited in growing tissues to TEE.