Data for U.S. women indicate that successful lactation occurs regardless of whether a woman is thin, of normal weight, or obese. Anthropometric measurements (such as weight, weight for height, and skinfold thickness) have not been useful for predicting the success of lactation among the few U.S. women who have been studied. The predictive ability is not known for anthropometric measurements that fall outside the ranges observed in these limited samples.
Lactating women eating self-selected diets typically lose weight at the rate of 0.5 to 1.0 kg (˜1 to 2 lb) per month in the first 4 to 6 months of lactation. Such weight loss is probably physiologic. During the same period, values for subscapular and suprailiac skinfold thickness also decrease; triceps skinfold thickness does not. Not all women lose weight during lactation; studies suggest that approximately 20% may maintain or gain weight.
Biochemical data for lactating women have been obtained only from small, select samples. Such data are of limited use in the clinical situation because there are no norms for lactating women, and the norms for nonpregnant, nonlactating women may not be applicable to breastfeeding women. For example, there appear to be changes in plasma volume post partum, and there are changes in blood nutrient values over the course of lactation that are unrelated to changes in plasma volume.
The mean volume of milk secreted by healthy U.S. women whose infants are exclusively breastfed during the first 4 to 6 months is approximately 750 to 800 ml/day, but there is considerable variability from woman to woman and in the same woman at different times. The standard deviation of daily milk intake by infants is about 165 ml; thus, 5% of women secrete less than 550 ml or more than 1,200 ml on a given day. The major determinant of milk production is the infant's demand for milk, which in turn may be influenced by the size, age, health, and other characteristics of the infant as well as by his or her intake of supplemental foods. The potential for milk production may be considerably higher than that actually produced, as evidenced by findings that the milk volumes produced by women nursing twins or triplets are much higher than those produced by women nursing a single infant.
Studies of healthy women in industrialized countries demonstrate that milk volume is not related to maternal weight or height or indices of fatness. In developing countries, there is conflicting evidence about whether thin women produce less milk than do women with higher weight for height.
Increased maternal energy intake has not been linked with increased milk production, at least among well-nourished women in industrialized countries. Nutritional supplementation of lactating women in developing countries where undernutrition may be a problem has generally been reported to have little