I was talking to some folks about the isotope values for Neandertals, and was immensely surprised to find out that nitrogen-15 (15N) proportions can be driven higher by weight loss.
Here's an abstract of an article from last year by Fuller and colleagues:
While past experiments on animals, birds, fish, and insects have shown changes in stable isotope ratios due to nutritional stress, there has been little research on this topic in humans. To address this issue, a small pilot study was conducted. Hair samples from eight pregnant women who experienced nutritional stress associated with the nausea and vomiting of morning sickness (hyperemesis gravidarum) were measured for carbon (delta13C) and nitrogen (delta15N) stable isotope ratios. The delta13C results showed no change during morning sickness or pregnancy when compared with pre-pregnancy values. In contrast, the delta15N values generally increased during periods of weight loss and/or restricted weight gain associated with morning sickness. With weight gain and recovery from nutritional stress, the hair delta15N values displayed a decreasing trend over the course of gestation towards birth. This study illustrates how delta15N values are not only affected by diet, but also by the nitrogen balance of an individual. Potential applications of this research include the development of diagnostic techniques for tracking eating disorders, disease states, and nitrogen balance in archaeological, medical, and forensic cases.
Last year, I reviewed some papers that documented high 15N values in Neandertals, which concluded that the high values may have resulted from mammoth and rhinoceros consumption. In another post, I explored the reasons why fish (also a high 15N dietary source) have been neglected as an explanation for the high Neandertal 15N values.
Now, the papers on these topics (e.g. Bocherens et al. 2005) have compared Neandertal isotopic ratios to those of other fauna from the same time period, so trophic level and other relations ought to be visible within this sample. But other evidence suggests that Neandertals were under high nutritional stress compared to most living human populations, including the high incidence of enamel hypoplasias, which are developmental deficits of tooth formation (Molnar and Molnar 1985).
Comparisons suggest that Neandertal nutritional stress was not outside the range of living populations, with a similarity in the proportion of linear enamel hypoplasia in Neandertal and Inuit samples (Guatelli-Steinberg et al. 2004). In isotopic terms, this is a difficult comparison, since Inuit do eat lots of fish, marine mammals and other 15N-enriched foods.
Another element of complexity is that 15N composition responds to weaning time, because breast milk is enriched in 15N content also. This effect diminishes during childhood after weaning, by around age 7-9, so it shouldn't affect adult Neandertal specimens, but I point it out because nutritional stress may also affect the age of weaning or dietary independence, which might conceivably deplete 15N in lactating women. One might imagine lactation balancing some of the 15N surplus resulting from pregnancy or nutritional stress.
So it may be awhile before we will know what the full effect of nutritional stress may be on these isotope values.
Bocherens H, Drucker DG, Billiou D, Patou-Mathis M, Vandermeersch B. 2005. Isotopic evidence for diet and subsistence pattern of the Saint-Césaire I Neanderthal: review and use of a multi-source mixing model. J Hum Evol 49:71-87.
Fuller BT, Fuller JL, Sage NE, Harris DA, O'Connell TC Hedges RE. 2005. Nitrogen balance and delta15N: why you're not what you eat during nutritional stress. Rapid Commun Mass Spectrom 19:2497-2506. PubMed
Guatelli-Steinberg D, Larsen CS, Hutchinson DL. 2004. Prevalence and the duration of linear enamel hypoplasia: a comparative study of Neandertals and Inuit foragers. J Hum Evol 47:65-84. PubMed
Molnar S, Molnar IM. 1985. The incidence of enamel hypoplasia among the Krapina Neandertals. Am Anthropol 87:536-549. JSTOR
Schurr MR. 1998. Using stable nitrogen-isotopes to study weaning behavior in past populations. World Archaeol 30:327-342.