Evolutionary traits in human milk proteins

Human milk has the lowest concentration of protein of any mammalian species. Since the rate of growth of the offspring is negatively related to the protein content of the milk, the time required to double the birth weight is greater in the infant than in any other mammal in which it has been measured. Similarly, in weaned animals, a low protein diet increases the time required to reach maximal growth, senescence and natural death. Human milk protein has the highest whey protein to casein ratio than the milk of any other mammalian species. Our previous experiments have shown that mice fed a 20% whey protein diet exhibit increased resistance to Streptococcus pneumoniae and a humoral immune response significantly higher than that of mice fed most of the commercially available animal and plant proteins in nutritionally similar and adequate formula diets. Other studies have demonstrated that mean and maximal longevity of hamsters fed a 20% whey protein diet is increased in comparison with those fed commercial laboratory feed or a supplemented casein diet of similar nutritional efficiency. Thus, the low protein content and the prevalence of whey protein, which are characteristic features of human milk, are both associated with slow body growth and increased longevity. For human infants, mother's milk is the first and, for most, the only food ingested for a considerable period of time. We, therefore, propose that a trace of Nature's design for the offspring and the evolution of the species can be found in mother's milk.(ABSTRACT TRUNCATED AT 250 WORDS)