Longitudinal Study of Stable Isotope Compositions of Maternal Milk and Implications for the Palaeo-Diet of Infants

Abstract

The classic interpretation of stable isotope data from young children in an archaeological context is based on the hypothesis that the nitrogen isotope ratios present in breast milk remain identical throughout the breastfeeding period. This exploratory study assesses the changes in the nitrogen and carbon isotope ratios in maternal milk and in the nails of the mother and child, with the aim to evaluate the impact of variations in the stable isotope ratios in maternal milk on the tissues of children, and consequently on the reconstruction of the palaeo-diet of young children. The results show that the isotopic composition of maternal milk diminishes in relation to the mother's tissues like nails and, by extrapolation, bones. The δ 15 N values of the milk vary little during the weeks of breastfeeding, but this is not the case for carbon, which varies considerably during the course of breastfeeding and weaning and does not seem to be linked to the mother's diet and/or to the height and weight of the child. The difference between the δ 15 N values recorded for the mother's and child's nails is less than 2‰, which is lower than the values often cited in bioarchaeological literature. In addition, the data from this study does not confirm the hypothesis of a significant increase in heavy isotopes in the nails of newborn babies in relation to those of their mother at childbirth.

Comparing apples and oranges: Why infant bone collagen may not reflect dietary intake in the same way as dentine collagen

“…The δ 13 C values are also less affected by any physiological changes than δ 15 N and thus a more robust measure of the expected changes seen during breastfeeding and weaning (although δ 13 C may fall if body fat is being recycled during periods of starvation; Beaumont & Montgomery, ). A further tentative explanation is that maternal physiology in the later stages of breastfeeding includes the mobilization of fat stores and a fall in the δ 13 C of breastmilk and thus the infant tissues as seen in the example by Herrscher et al ().…”

“…This will have the effect of increasing the δ 15 N values in the same way as a trophic level shift (and see discussion in Katzenberg & Lovell, ). A recent publication has also shown the relationship between the isotope ratios in breastmilk and the maternal and infant fingernails, albeit in a single modern pair (Herrscher, Goude, & Metz, ). This provides evidence for the stability of the δ 15 N values in breastmilk in this well‐nourished pair, with a smaller than expected shift in δ 15 N between maternal and infant fingernails.…”

The Whole Tooth and Nothing but the Tooth: Or why Temporal Resolution of Bone Collagen May Be Unreliable

“…This could be a better method for finding the age at which exclusive breastfeeding ceases, but against this argument are the findings of the breastmilk study by Herrscher et al . () where maternal physiology in the later stages of breastfeeding includes the mobilization of fat stores and a fall in the δ 13 C of breastmilk and thus the infant tissues.…”

Reconstructing breastfeeding and weaning practices in the Bronze Age Near East using stable nitrogen isotopes

“…The principle of investigating weaning using nitrogen stable isotope values (reported as δ 15 N in parts per thousand, ‰) is that an infant consuming its mother's breast milk is one trophic level higher than her own tissues. As animals within a food web display δ 15 N values ~3–5‰ higher than their prey (Bocherens & Drucker, ; Minagawa & Wada, ; Perkins et al, ), it follows that breastfeeding practices and age‐at‐weaning can be extrapolated using this stepwise nitrogen enrichment (Dupras & Tocheri, ), although studies of modern mothers and children found maternal milk δ 15 N composition to vary and generally be 2‰ lower than infant tissues rather than the expected 3–5‰ (Herrscher, Goude, & Metz, ). Stepwise nitrogen enrichment from being breastfed has been observed in living populations, with fetal and neonatal δ 15 N values showing a strong relationship with maternal δ 15 N values (de Luca et al, ; Fogel, Tuross, Johnson, & Miller, ; Fuller, Fuller, Harris, & Hedges, ).…”