Determinants of energy, protein, lipid, and lactose concentrations in human milk during the first 12 mo of lactation: the DARLING Study

Article Abstract:

The nutrient content of human milk can vary greatly even within well-nourished populations. Because the energy and protein content of milk is critical for the normal development of infants, it is important to determine what factors influence the content of these and other nutrients in human milk. Few conclusions have been made about these factors, partly due to the difficulty in obtaining 24-hour milk samples. The composition of milk varies within feedings as well as at different times of day. To better characterize determinants of human milk components, a long-term study was conducted, using data from the DARLING (Davis Area Research on Lactation, Infant Nutrition and Growth) Study. Three months postpartum, variation in milk lipid (fat) was related to maternal fatness, and at 12 months, lipid content was seen to decrease as the number of previous deliveries went up. Protein levels, after three months, were positively related to nursing frequency and negatively related to milk volume. Lactose (milk sugar) levels were correlated with milk volume at six and nine months, and lactose was lower at nine months in mothers who had resumed menstruation. Energy and lipid concentrations were significantly related to maternal intake of protein and proportion of calories derived from protein, and the protein intake-lipid association was more robust in mothers who were over 16 weeks postpartum. The study indicates that milk composition is more sensitive to maternal factors as the postpartum period lengthens and weight gained during pregnancy is lost. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Studies in human lactation: milk composition and daily secretion rates of macronutrients in the first year of lactation

Article Abstract:

This article describes the results of a study designed to determine the composition of human breast milk, and the changes in milk composition that occur during the first year of breast-feeding. The study included 13 nonsmoking women who had previously breast-fed at least one infant. Breast milk samples were obtained using an electric breast pump. Three samples from each woman were collected prior to the infant's birth. Milk samples were then collected twice a day for the first three days after delivery, once a day until day seven, every other day until day 14, once a week until week eight, and once a month for the remainder of the year. In the period just prior to delivery, the milk samples contained large amounts of protein, sodium and chloride, and small amounts of glucose (sugar), lipid (fat) and citrate. During the first month following delivery, the amount of glucose, lactose (another type of sugar), lipid, citrate and calcium increased, while the amount of protein, sodium, potassium, citrate and chloride decreased. During the remainder of the year the composition of the milk remained fairly constant. There were individual differences in the amount of sodium, potassium, chloride and phosphate present in the milk. Also, the amount of lactose, ionized calcium, and magnesium transferred to the infant, by way of breast milk, varied from mother to mother. It is concluded that the composition of human milk changes during the first month following delivery and then remains relatively constant for the rest of the first year. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Lactation performance of exercising women

Article Abstract:

Many women wish to lose weight after giving birth. Especially for nursing mothers, exercise is recommended as a better means of losing weight than dieting. This is because good nutrition is necessary to support lactation, and dieting can interfere with the process. However, some clinicians have expressed concern that the stresses and physiological changes which occur during exercise may also interfere with lactation. This question was examined among eight exercising and eight sedentary mothers, all with exclusively breast-fed children aged between 9 and 24 weeks. The two groups differed significantly in a number of ways. The exercising group had less body fat. The exercising women also both consumed and expended more calories than the sedentary group. The average daily consumption was 2,739 calories for the exercising group and 2,051 calories for the sedentary group. Daily caloric expenditure was 3,169 for the exercising group as compared with 2,398 for the sedentary group. However, these differences did not appear to affect lactation. There were no differences between the groups in blood hormone levels or milk energy, fat, protein, or lactose (milk sugar) content. The exercising women, in fact, produced a slightly greater amount of milk (839 versus 776 grams per day). Thus, there was no evidence that exercise by nursing mothers will have adverse effects on lactation. (Consumer Summary produced by Reliance Medical Information, Inc.)

Exercise, Exercise physiology

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