Weight gain and chemical changes in low birthweight infants after change from human milk to modified cow's milk.

Weight gain and some biochemical changes were observed in 7 preterm infants of low birthweight when their diet was abruptly changed from one of human milk to a modified cow's milk formula. There was a fall in the serum calcium and a rise in the inorganic phosphate levels in the week after the changeover. Serum sodium was raised after two days, with a fall occurring over the following 5 days. Blood urea rose throughout the 7-day period. Accompanying these biochemical changes there was an acceleration in weight gain, and in 5 infants this was associated with peripheral oedema. In the second week after the changeover there was a deceleration in weight gain accompanied by loss of the oedema. Immaturity of certain homeostatic mechanisms required to cope with the higher protein and electrolyte content of the modified cow's milk accounts for these observations. A more gradual dietary changeover, therefore, seems advisable.