Basal and postprandial metabolic rates in lactating and nonlactating women

Article Abstract:

The energy requirements for maintaining appropriate nutrition and adequate milk production during lactation are not known. The total daily energy needs were estimated at 40 to 44 kilocalories per kilogram (kcal per kg) of body weight for lactating women, compared with 34 to 38 kcal/kg body weight for nonlactating women. The basal metabolic rate (BMR) accounts for the largest component of total daily energy expenditure in adult women who are excessively active. BMR is the metabolic rate measured under basal conditions, such as 12 hours after eating, after a restful sleep, in the absence of exercise or emotional excitement, and in a comfortable temperature. This measurement reflects the function of the thyroid gland, and ranges from 18 to 31 kcal per kg body weight in lactating women from developing countries to 23 kcal per kg body weight in lactating women from developed countries. The energy necessary for lactation consists of the energy content of the milk and the energy needed to produce and secrete the milk. Although 40 to 44 kcal per kg body weight was estimated as the energy necessary for meeting the needs of a healthy lactating woman, some studies have suggested that this is too low. The effects of lower levels of energy intake on the mother are not known. The BMR and postprandial metabolic rates (PMR; after a meal) were assessed in lactating and nonlactating women after childbirth, and women who did not undergo childbirth. The women were placed on a diet of known protein content, and their energy intake levels were determined by diet records. The production of milk was also measured. Although BMR was similar among all groups of women, PMR was higher in lactating women than in nonlactating women and related to the levels of nitrogen in milk. The energy consumed to produce milk was 125 percent of the energy content of milk. Thus, the increased energy needs of lactating women are due to milk production and increased PMR; this energy requirement was associated with a 50 percent increase in dietary energy intake. (Consumer Summary produced by Reliance Medical Information, Inc.)

Basal metabolism, Mothers

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Dietary protein and nitrogen balance in lactating and nonlactating women

Article Abstract:

During lactation, women need additional calories and nutrients in order to produce breast milk and maintain their own nutrition. The amount of dietary protein needed daily (Recommended Dietary Allowance, RDA) by a lactating woman has been estimated at 1.0 gram per kilogram of body weight (gm/kg). This is higher than the RDA for nonlactating women, which is 0.8 g/kg. But the method used to calculate the protein needs of breast-feeding women may not have been sufficiently accurate. The theoretical calculations involved adding the amount of protein in breast milk to the protein requirements of a nonlactating woman. But what happens in the human body during lactation was not observed; it may be that actual protein metabolism does not reflect this theory. The standard for evaluating actual protein metabolism in the individual is a method called nitrogen balance. Nitrogen is always present as a component of proteins, making up 16 percent of all proteins, thus the amount of nitrogen reflects the amount of protein. Nitrogen balance involves measuring the nitrogen consumed in food, and the amount excreted in the urine. If these amounts are equal, the individual is in balance. A positive result, indicating that more nitrogen is consumed than is excreted, indicates growth or healing because protein tissues are being built in the body. The reverse, greater losses than intake of nitrogen, indicates that tissues are being broken down as occurs in disease or malnutrition. Nitrogen balance studies were done on 12 healthy women who were breast-feeding their infants and nine healthy nonlactating women. All subjects received a controlled diet supplying 1.0 gm/kg/day of protein. The lactating women had lower nitrogen balance values than the nonlactating group, which suggested that the amount of protein that was provided (equal to the RDA) may be inadequate to support the needs of healthy breast-feeding women. (Consumer Summary produced by Reliance Medical Information, Inc.)

Case studies, Women, Breast feeding, Nutritional aspects, Nitrogen metabolism, Proteins in human nutrition, Dietary protein

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Vitamin K in colostrum and mature human milk over the lactation period - a cross-sectional study

Article Abstract:

The levels of vitamin K were measured in the milk of four groups of mothers between one day and six months after childbirth. A total of 60 women participated. Vitamin K levels averaged 7.52 nanomoles per liter (nmol/L) in colostrum, the earliest milk which is released in the first few days after delivery, and 6.36 nmol/L in mature milk (produced from about one to two weeks postpartum on). However, this difference in vitamin K content between colostrum and mature milk was not significant, nor were differences among mature milk samples obtained at one, three, and six months after childbirth. However, twice as much vitamin K was provided to the infant in mature milk as in colostrum, because the volumes of milk secreted increased over the lactation period (colostrum is secreted in very small quantities). The levels of vitamin K in breast milk were not related to the intake of fat and vegetables in the mother's diet. Vitamin K levels in colostrum were related to the fat content of the colostrum. Vitamin K accumulated in the lipid portion of the milk fat globule but not within the membranes. These findings suggest that the amount of vitamin K in human milk is inadequate and does not fulfill the recommended requirements for infants less than six months of age. Current recommendations for vitamin K intake by infants who are fed only breast milk must be reassessed. (Consumer Summary produced by Reliance Medical Information, Inc.)

Infants, Breast milk, Vitamin K, Colostrum

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