SUBSTRATE UTILIZATION DURING THE FIRST WEEKS OF LIFE

It is assumed that substrate utilization changes markedly around birth , from mainly glucose utilization before, to glucose/fat utilization a fter birth. We studied substrate oxidation and turnover in preterm inf ants on the first day and during the first weeks of life. We found tha t only part of the glucose that is infused on the first day of life is oxidized, while glucose is also converted into fat at the same time. Almost half of the energy expenditure is provided by fat oxidation on day 7 and 28 of life. Fat oxidation is dependent on the type of fat ox idized; the rate of oxidation of medium chain triglycerides (MCT) is h igher than that of long chain fatty acids. MCT can replace glucose as an energy source. Proteins contribute only to a small extent (approxim ately 7%) to the energy expenditure at all ages.