The diet‐body offset in human nitrogen isotopic values: A controlled dietary study

Abstract

The "trophic level enrichment" between diet and body results in an overall increase in nitrogen isotopic values as the food chain is ascended. Quantifying the diet–body Δ15N spacing has proved difficult, particularly for humans. The value is usually assumed to be +3–5‰ in the archaeological literature. We report here the first (to our knowledge) data from humans on isotopically known diets, comparing dietary intake and a body tissue sample, that of red blood cells. Samples were taken from 11 subjects on controlled diets for a 30-day period, where the controlled diets were designed to match each individual's habitual diet, thus reducing problems with short-term changes in diet causing isotopic changes in the body pool. The Δ15Ndiet-RBC was measured as +3.5‰. Using measured offsets from other studies, we estimate the human Δ15Ndiet-keratin as +5.0–5.3‰, which is in good agreement with values derived from the two other studies using individual diet records. We also estimate a value for Δ15Ndiet-collagen of ≍6‰, again in combination with measured offsets from other studies. This value is larger than usually assumed in palaeodietary studies, which suggests that the proportion of animal protein in prehistoric human diet may have often been overestimated in isotopic studies of palaeodiet. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.

Multi-isotopic analysis of first Polynesian diet (Talasiu, Tongatapu, Kingdom of Tonga)

“…When compared to the two pigs values, the Talasiu human values are more positive for both carbon (+4.0‰) and nitrogen (+2.9‰). We observe a much higher enrichment in 13 C (+4.0‰ versus 0-2‰) than the expected enrichments between two consecutive trophic levels which are between 0 and to 2‰ for carbon and 3-6‰ for nitrogen (Bocherens and Drucker, 2003;O'Connell et al, 2012). This observation, confirming a non mono-isotopic human diet, indicates a contribution of dietary resources with isotopic values very different from terrestrial animal isotopic values.…”

“…Theoretical nitrogen isotope fractionation may vary from 3 to 6‰ between food and consumer (Bocherens and Drucker, 2003;O'Connell et al, 2012) while carbon isotope fractionation is only +0-2‰ (Bocherens and Drucker, 2003) between food and consumer. Collagen carbon isotope ratios also include a + 5‰ offset due to fractionation during carbon incorporation into collagen.…”

Isotopic anthropology of rural German medieval diet: intra- and inter-population variability

“…If the Dalheim population had subsisted primarily on C 3 plants, the average nitrogen-isotope composition would resemble that of terrestrial herbivores (e.g., cows or sheep). Because nitrogen-isotope compositions increase by~+3 to +6‰ between trophic levels (DeNiro and Epstein 1981;Schoeninger 1985;O'Connell et al 2012), the human nitrogen-isotope composition at Dalheim is consistent with the regular consumption of terrestrial mammal protein. The low δ 15 N col among juveniles (children 7 to 12 years old) at Dalheim suggests that they consumed protein from lower trophic levels relative to younger adults (20 to 40 years old).…”

“…Isotopic variation begins at the base of the food chain where plant δ 15 N normally ranges from about −3 to +6‰ on average in pre-industrial ecosystems (Virginia and Delwiche 1982;Heaton 1987;Ambrose 1993). In general, δ 15 N col is~3 to 6‰ higher than diet, and the δ 15 N col of carnivores tends to be higher than those of omnivores which, in turn, are higher than those of herbivores in terrestrial populations (DeNiro and Epstein 1981;Schoeninger 1985;O'Connell et al 2012). Higher δ 15 N col among humans consuming primarily vegetarian diets could reflect the consumption of domesticated crops grown using animal manure, which could increase plant δ 15 N by~3 to 5‰ (Bogaard et al 2007).…”

Stable Isotope Analysis: Outline of Methodology, and a Review of Studies in Siberia and the Eurasian Steppe

“…Значения δ 15 N у современных растений колеблются в преде-лах 0-5 ‰. В результате фракционирования на каж-дом трофическом уровне происходит увеличение δ 15 N на 3-6 ‰ [Hedges, Reynard, 2007;O'Connell et al, 2012]. Таким образом, у людей, потребляющих мясо наземных травоядных, данный показатель будет при-близительно равен 9 ‰, хотя это зависит от изотопно-го состава азота в местных растениях.…”