Casein to whey protein ratio in rat and human milks: effects of maternal protein intake

Maternal diet may affect milk composition quantitatively and qualitatively. The aim of this study was to assess the effects of different dietary protein quality and quantity on total milk protein concentration and on possible changes in casein:whey protein ratio as a result of differences in maternal nutritional status. Milk samples were obtained from Wistar rats fed either wheat gluten or supplemented casein at different percentages. A similar analytical scheme was applied to milk samples from lactating women belonging to different socioeconomic classes. Total milk protein in rat milk was related closely to protein quality and, to a lesser extent, to protein quantity, showing significant differences among treatment groups. Relative proportions between milk proteins were significantly affected by diet: casein: whey protein ratio was related positively to protein quality and quantity. In human milk, even though total protein content did not differ, the relative proportions between milk proteins were altered, but in a way opposite to that observed in rat milk: the whey protein:casein ratio was related positively to maternal protein intake. These modifications might influence the nutritive value or anti-infectious properties of the milk ingested by the neonate.