The recommended dietary allowances of many expert committees (UK DHSS 1979, FAO/WHO/UNU 1985, USA NRC 1989) have set out the extra energy requirements necessary to support lactation on the basis of an efficiency of 80 per cent for human milk production. The metabolic efficiency of milk synthesis can be derived from the measurements of resting energy expenditure in lactating women and in a matched control group of non-pregnant non-lactating women. The results of the present study in Gambian women, as well as a review of human studies on energy expenditure during lactation performed in different countries, suggest an efficiency of human milk synthesis greater than the value currently used by expert committees. We propose that an average figure of 95 per cent would be more appropriate to calculate the energy cost of human lactation.
PIP: A case control study of 16 lactating women (2 months postpartum) and 16 nonlactating women living in keneba, a rural village in the Gambia, was conducted to determine the metabolic efficiency of breast milk synthesis using calorimetric data. Even though marginal dietary intakes occurred in this community, mean breastfeeding duration ranged from 18 to 24 months with daily milk production similar to that of European women. The women in the study spent 24 hours in a whole body indirect calorimeter where the test weighing technique measured breast milk production in each lactating woman. This technique operated under the appropriate assumption that milk is synthesized continuously in humans regardless of suckling or not. Mean breast milk production stood at 738 g (give or take 47 g) 70 days postpartum. Basal metabolic rate was comparable for both cases and controls (3.81 and 3.71 respectively). Milk energy density stood at 2.9kJ/g. The average efficiency of milk production stood at 94.2% (give or take 3.5g). At least 3 other studies, also found efficiency of milk production to be 90%. Yet the FAO/WHO/UNU Expert Consultation, the UK Department of Health and Social Security, and the US National Research Council committees have determined recommended dietary allowances based on 80% efficiency of milk production. Using the Gambian study's percentage, the energy requirements for milk synthesis in lactation would fall around. 400 kJ/day (almost 20% of the allowances of FAO/WHO/UNU). It is concluded that scientists should use 95% to calculate the energy cost of human lactation.