Is human lactation a particularly efficient process

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 studys 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.