Early influences of nutrition on postnatal growth.

Health and nutrition modulate postnatal growth. The availability of amino acids and energy, and insulin and insulin-like growth factor-I (IGF-I) regulates early growth through the mTOR pathway. Amino acids and glucose also stimulate the secretion of IGF-I and insulin. Postnatal growth induces lasting, programming effects on later body size and adiposity in animals and in human observational studies. Rapid weight gain in infancy and the first 2 years was shown to predict increased obesity risk in childhood and adulthood. Breastfeeding leads to lesser high weight gain in infancy and reduces obesity risk in later life by about 20%, presumably partly due to the lower protein supply with human milk than conventional infant formula. In a large randomized clinical trial, we tested the hypothesis that reduced infant formula protein contents lower insulin-releasing amino acid concentrations and thereby decrease circulating insulin and IGF-I levels, resulting in lesser early weight gain and reduced later obesity risk (the 'Early Protein Hypothesis'). The results demonstrate that lowered protein in infant formula induces similar - but not equal - metabolic and endocrine responses and normalizes weight and BMI relative to breastfed controls at the age of 2 years. The results available should lead to enhanced efforts to actively promote, protect and support breastfeeding. For infants that are not breastfed or not fully breastfed, the use of infant formulas with lower protein contents but high protein quality appears preferable. Cows' milk as a drink provides high protein intake and should be avoided in infancy.