Protein intake and growth in the first 24 months of life

Nutritional and metabolic factors acting during pre- and postnatal life predict long-term health outcomes. The increasing prevalence of obesity has raised strong interest in early programming, in particular with regard to potentially modifiable variables that would offer effective prevention. Maternal factors such as high maternal prepregnancy body mass index and gestational weight gain, or intrauterine energy and protein deficiency have all been associated with an increased risk of insulin resistance and obesity in the offspring. Infant feeding also modulates later obesity risk. A report by the World Health Organization in 2007 concluded that breastfeeding may have a small protective effect on the prevalence of later obesity (1). Obviously, potential residual confounding factors that cannot be fully adjusted for may contribute to this effect. However, the specific compositional aspects of breast milk, such as the lower protein content, as compared with infant formula or endocrine agents, which are only present in human milk, such as insulin-like growth factor 1, leptin, ghrelin, and adiponectin, could affect the regulation of energy intake and expenditure and the growth pattern of the infant. Undisputable proof for a causal protective effect of breast-milk components remains difficult to obtain; however, understanding those causalities may strengthen the conclusions on the protective effects of breast-feeding. Moreover, this knowledge may help to improve the practice of feeding formula and complementary foods for infants. Formula-fed children grow faster during the first 2 years of life than breast-fed children, and they are at a higher risk for later obesity. More rapid growth in infancy, especially weight gain, has also been shown to increase the risk of later obesity. Given that formula-fed infants have markedly higher protein intakes than breast-fed infants, we followed the hypothesis that their different early growth and later obesity risk may be explained, at least in part, by the higher protein intake in infancy. Protein intake stimulates the insulin and insulin-like growth factor 1 metabolism and consecutively leads to cell proliferation, accelerated growth, and increased adipose tissue.