Milk and Growth in Children: The Effects of Whey and Casein

Consumption of cow's milk in childhood is recommended in many countries. Cow's milk has a content of protein and minerals needed for growth with protein content about three times as high as the content in breast milk. Furthermore, the ratio between whey and casein is very different, 20/80 and 60/40 in cow's milk and human milk, respectively. In infant formula, both the amount and the whey/casein ratio have been adjusted to be close to human milk because it is suggested that the composition of human milk is optimal for healthy growth in infants. However, the type and content of specific proteins in the whey and casein fractions are also different in cow's milk compared to human milk. A review published a few years ago [1] summarizing observational and intervention studies concluded that cow's milk most likely has a positive influence on growth in children. The strongest evidence comes from observational studies and intervention studies in low-income countries, but there are also observational studies from high-income countries showing an association between milk intake and growth [1, 2]. A new study from the US with young girls also found that among different nutrients/foods examined, the growth in height was strongest associated with dairy protein [3]. However, the effect of milk on growth may not be the same in all age groups [4]. Thus, milk seems to have a specific stimulating effect on linear growth, not only in developing countries with high rates of malnutrition, but also in industrialized countries [1]. It is not known which components in milk may have the growth-stimulating effects. Possible components are proteins/peptides, minerals (calcium, phosphor), vitamins or combinations of these. In relation to protein quality and growth, several indexes for protein quality based on the amino acid composition have been used, e.g. PDCAAS [2]. According to most of these indices, whey has a slightly higher quality