Protein quality of breast milk is superior to that of formula proteins. To ensure that the protein intake is sufficient, starter formulas with conventional protein composition provide a protein/energy ratio of 2.2-2.5 g per 100 kcal to infants, which is much higher than that supplied with breast milk. Several studies have shown that formula-fed infants have higher plasma or serum urea concentrations than breast-fed infants do. We tested if feeding formulas with improved protein quality and a protein content corresponding to the minimum level that is consistent with international recommendations (1.8 g/100 kcal) allows patients to achieve normal growth and plasma urea concentrations.
Healthy term infants were enrolled into the study and were either breast-fed or randomly assigned to three formula-fed groups. Formula-fed infants received either a standard formula with a protein/energy ratio of 2.2 g/100 kcal, whereas the two other groups received formulas with a protein/energy ratio of 1.8g/100 kcal differing mainly by their source of protein. Subjects received breast milk or these formulas ad libitum as the sole source of energy from birth to four months of age in a controlled blind design (except for the breast-fed group). Anthropometric measurements (body weight and length) were obtained at birth, at 30, 60, 90, and 120 days. Energy and protein intakes were calculated from three-day dietary records. Blood was collected for biochemical measurements at 30, 60, and 120 days.
No differences were found between the four feeding groups for weight- and length-gains or for body mass indices (BMI). No differences in energy intakes between the formula-fed groups could be found, whereas protein intakes were less in infants fed the 1.8 g/100 kcal formulas. Plasma urea levels of the infants fed the 1.8 g/100 kcal formulas were closer to those found in the breast-fed infants.
Improvement of the amino acid profile permits a whey predominant starter formula with 1.8 g protein per 100 kcal to meet the needs of normal term infants during the first four months of life.