Studies conducted in the United States, other developed countries, and developing countries indicate that the average level of milk production is approximately 750 to 800 ml/day in women with widely varying dietary intakes and with varying nutritional status, as measured by weight and skinfold thickness.
Potential production of milk by lactating women appears to be considerably higher than actual intakes by single infants, as indicated by the high milk volumes produced by women nursing twins or even triplets.
Factors other than maternal nutrition affect milk volume and should be considered in any evaluation of lactation performance. Maternal age and parity appear to have little, if any, influence, but variables such as maternal stress and the nursing behavior of both mother and infant are potentially important.
Maternal nutritional status, as measured by anthropometric indices prenatally or post partum, is not related to milk volume in studies conducted in industrialized countries such as the United States. In other words, infants of thin women generally consume as much breast milk as infants of normal-weight or overweight women. In less developed countries, the results are mixed; some studies show a positive association between maternal body composition (adiposity) and milk volume.
Average milk volumes of lactating women are comparable in industrialized and developing countries, despite substantial differences in energy and nutrient intake. This suggests that maternal energy intake is not strongly associated with milk volume. Studies in animals indicate that there may be a threshold below which energy intake is insufficient to support normal milk production; it is likely that most studies in humans have been conducted in groups with intakes above this hypothesized threshold.
Food supplementation of lactating women in areas where malnutrition is prevalent has generally had little, if any, impact on milk volume. However, such supplementation may improve maternal health and therefore is more likely to benefit the mother than the infant, except in cases in which milk composition is affected (see Chapter 6).
It is customary to lose weight gradually during lactation. In the United States, lactating women tend to be heavier than their ideal body weight immediately post partum, and some successfully lose up to 2 kg (˜4.5 lb) per month with no apparent deleterious effects on milk production.
Women who exercise regularly appear to produce an adequate volume of milk.
The influence of maternal intake of specific nutrients on milk volume has not been investigated thoroughly. Early studies in developing countries show an association of protein intake with milk volume, but limitations of the study designs prohibit definitive conclusions.