Infant formula with protein-energy ratio of 1.7 g/100 kcal is adequate but may not be safe

An adequate protein-energy ratio of infant formulas has been defined as one that permits growth similar to that of infants fed relatively generous protein-energy ratios, and serum concentrations of albumin and urea nitrogen no less than those observed in breast-fed infants. A safe ratio has been defined as one with no detectable adverse effects. The hypothesis was that a protein-energy ratio of 1.7 g/100 kcal is adequate and safe.

Healthy male infants were fed Formula 1.7, a milk-based formula, as the sole source of energy from the 8th to the 112th day of life. Weight, length, and energy intake were measured; serum albumin and urea nitrogen were determined; and the results were compared with data from appropriate reference groups of infants.

Energy intake from 8 through 55 days was significantly higher than that of infants in the formula-fed reference group. Gain in weight was significantly more than that of the formula-fed reference group or of a breast-fed reference group, whereas gain in length was similar to that of the formula-fed reference group. Body mass index was significantly higher than that of either reference group, suggesting more fat accumulation in infants fed Formula 1.7. Plasma concentrations of albumin and urea nitrogen were similar to those of the breast-fed reference group.

Infants fed Formula 1.7 received adequate intakes of protein. Because of the possibility that ad libitum feeding of diets with moderately inadequate protein-energy ratios is associated with increased food intake leading to excess weight gain, it is not possible to conclude that a protein-energy ratio of 1.7 g/100 kcal is safe.