Fertility-related changes in maternal body composition among the Au of Papua New Guinea

Evolutionary theory predicts that organisms make trade-offs between their somatic and reproductive energy budgets. Thus every round of reproduction should result in a concomitant decline in the parents' total energy reserves. Among humans this prediction was corroborated more than 25 years ago when fertility-related nutritional depletion was reported among mothers in the Highlands of New Guinea (Jelliffe and Maddocks, 1964). More recently, however, a number of studies of fertility and maternal nutritional status in both developed and developing nations have reported fertility-related increases in various indices of adiposity and lean body mass. Such findings have called the so-called "maternal depletion syndrome" into question, and have raised serious doubts as to whether the phenomenon is widely generalizable to all populations. In light of this recent controversy, data are presented here on fertility-related changes in maternal adiposity and lean body mass among the Au, a lowland forager-horticulturalist population in Papua New Guinea. While both a short-term decline in adiposity following childbirth, and a long-term fertility-related decline are seen among more traditional Au, individuals with a regular source of wage-income show only the former. There are no significant changes in lean body mass with increasing fertility in either group. The finding of significant socioeconomic variation in the capacity to withstand the stress of repeated reproduction even within this one extremely rural area of Papua New Guinea may lend insight into why previous studies have been unable to find evidence of maternal depletion. The fertility-related decline in adiposity that is reported for the more traditional Au is consistent with the predictions of evolutionary theory.