[The effect of lactation time on the macronutrient and mineral composition of milk from Venezuelan women].

Human milk is considered the ideal food for the infant and it has been extensively used to estimate its nutrient requirements. The objective of this paper was to determine the effect of lactation time on the macronutrient an mineral content of milks obtained from Venezuelan women and also to compare this with the established nutrient requirements of the infant. For this purpose 83 milk samples from 45 low income mothers were analyzed at the colostrum (48 h to 54 d) and mature states of lactation (1.3 and 6 months). The results showed that colostrum had a higher protein and a lower fat content than mature milks whereas its content of energy and carbohydrate was similar to mature milk. The iron and calcium content of the milk remained unchanged during the whole study whereas Zn and Cu decreased and increased with lactation time respectively. In contrast, phosphorous and magnesium increased up to 3rd month of lactation and remained constant there after. The macronutrient content of 850 ml of the analyzed milk almost completely fulfilled the daily infant requirements established in the US (RDA) and Canada (RNI). The mineral content of this volume of milk however was insufficient to cover the infants requirements particularly those established in the US. The most notorious deficiency in these milks was in Fe since they could fulfill only 11% the infants RDA for this mineral. The infant mineral requirements established in Canada are substantially lower than those defined in the US and therefore the analyzed milks could totally fulfill the Canadian infant daily requirements of Mg, Fe and Ca and more than 70% and 80% of the requirements of Zn and P. In general, the results of this study showed that the nutrient content of the analyzed milks agree well with those reported in the literature for women from different parts of the world including developed and underdeveloped areas. At the same time they pointed out the differences in the definition of the infant nutrient requirements set by different countries and also emphasize the fact that human milk, which by definition is the natural source of nutrients for the human infant apparently is incapable of fulfilling its daily requirements.