300% or more. Thus, a similar reduction in energy intake as a percentage of total intake is likely to result in a smaller decrease in milk volume of humans and other primates than of litter-bearing animals.
Observational studies of the relationship between maternal energy intake and milk volume in human populations have yielded mixed results. Despite much lower reported energy intakes among women in developing countries compared with their counterparts in industrialized countries, average milk volumes of both groups at 3 months post partum are similar (Prentice et al., 1986, see Figure 5-2). In industrialized countries, Strode et al. (1986) found no association between maternal energy intake and infant milk intake, whereas Butte et al. (1984a) and Prentice et al. (1986) reported a weak correlation in early lactation. Such an association may reflect reverse causation: women who produce more milk might consume more food because of greater appetite. (In rats, food intake is stimulated by lactation [Roberts and Coward, 1985] or by experimentally manipulating levels of serum prolactin [Moore et al., 1986].) In The Gambia, Prentice and colleagues (1986) found a striking association between seasonal patterns of maternal energy intake and infant milk intake but concluded that this association reflected changes in breastfeeding patterns and infant illnesses rather than maternal undernutrition.
There have been several attempts to document the effects of famine on milk volume, but quantitative data are generally lacking. Historical accounts of mothers breastfeeding during wartime sieges in Europe provide mostly anecdotal evidence of insufficient milk production among some women (Gunther, 1968). Dean (1951) reported that milk volume measured at a maternity clinic in Wuppertal, Germany, on the seventh day post partum was about 60 g lower during the war (1945-1946) than before it (1938). Severe undernutrition is widely regarded as detrimental to milk production, but there are very few supporting data.
Short-term fasting has been the subject of a few investigations. In The Gambia, Prentice et al. (1983c, 1984) reported that milk volume was unaffected in women during Ramadan, when no food or fluid is consumed from 5 a.m. to 7:30 p.m. (although intake after 7:30 p.m. may be considerable). Similarly, Neville and Oliva-Rasbach (1987) found that the rate of milk secretion was no different from the baseline among five lactating women who ate no food for 20 hours.
Strode and colleagues (1986) examined the effects of energy restriction among presumably well-nourished mothers. The experimental group reduced their energy intake by an average of 32% (range, 19 to 53%) below baseline intakes for 1 week; the control group maintained their usual intake. Among the eight mothers who restricted their intake to no less than 1,500 kcal/day, there was no reduction in milk intake by their infants, but levels of plasma prolactin tended to increase relative to those of control mothers. However, milk intakes by infants of the six mothers who decreased their energy intake below