Infant growth is associated with protein intake. Protein in breast milk decreases sharply within the first few weeks and then becomes steady at 6-12 months at 1.4-1.5g/100kcal. If mothers continue breastfeeding in the second year of life, those children will get a significant part of their calories from breast milk that is low in protein.
From cohort studies, some observations have been made regarding the effects of high protein vs. low protein intake and its long-term effect on growth. Low protein intake through breastfeeding during the first 2 years of life showed a prevention of accelerated growth during infancy. In one study, a group was maintained on a <16% protein and the other >16% protein. It was found that during early life, there was not a significant difference between the two groups. However, 20 years later it was possible to see a significant difference between the two group’s BMI where the groups maintained on a >16% protein diet had a higher BMI than the low protein group.
The new generation of infant formulas have decreased the protein content and increased the quality of the protein to bring it closer to breast milk composition. From randomized control trials it has been found that there is a significant difference in weight gain between low protein formula fed infants and high protein formula fed infants as well as significant difference in BMI at 72 months.