Energy balances were performed on sixteen low birth weight preterm infants over 7-10 d periods on a standard low-solute infant formula (2600 kJ/l), and on four high-energy formulas, providing different energy densities up to 3760 kJ/l. In two of the high-energy formulas the additional fat energy was provided by peanut oil, and the other two by medium chain triglycerides (MCT). Anthropometric measurements and metabolic rate (MR) determinations were made during the balance periods. 2. Mean energy retention on the standard formula was 66% of the intake and declined to below 50% on the two feeds providing the highest energy. Extensive energy balance data on the standard formula are available for reference. 3. Net absorption of dietary energy increased on all the high-energy formulas, rising from 362 kJ/kg per d on the standard formula to 453 kJ/kg per d on the highest energy-formula (P < 0.001). There was no advantage in using MCT. 4. Net absorption of dietary energy improved with advancing maturity, irrespective of the formula. 5. In spite of the increased dietary energy retention, there was no increase in growth rate during periods of feeding with the high-energy formulas. 6. Fasting and postprandial MR increased by 10.4 and 12.8% respectively on the highest energy feeds. 7. It is concluded that, at least in the short term, this type of high-energy feeding increases MR at the expense of growth and thus is probably of no advantage to the infant.
