The capacity of lipolysis and ketogenesis as well as blood glucose homeostasis is studied in full-term newborn infants on different feeding formulas during the first days of life. Only with the aid of an oligosaccharide compound, carbohydrates can be administered in sufficient quantities, about 7 g/kg X 24 h, so that fat mobilization and ketogenesis are almost completely suppressed. This is not achieved by a regimen mimicing breast feeding in that no milk feeding takes place during the first day, nor by feeding maximal quantities of milk as soon as possible nor by administration of a mixed formula consisting of 10% glucose and milk. Though by early ingestion of large volumes of milk which without introducing tube feeding cannot be further enhanced total caloric intake almost equals the amount attained by the oligosaccharide formula the proportion of carbohydrates in respect to the latter only amounts to one third. In summing up the data reported herein demonstrate that the energy requirements of neonates cannot be supplied by usual dietary regimens, mainly due to the limitation of volume newborn infants can drink voluntarily. As a result of a deficiency in available carbohydrate lipolysis is stimulated in adipose tissue and ketosis arises. These are physiological adaptions resulting in increased availability of free fatty acids and ketone bodies which are easily utilized and thus satisfy the caloric requirements of the newborn infant.