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

• Published in: American journal of physical anthropology 2012-11, Vol.149 (3), p.426-434
• Main Authors: O'Connell, T.C., Kneale, C.J., Tasevska, N., Kuhnle, G.G.C.
• Format: Article
• Language: English
• Subjects: Adult; Aged; Anthropology, Physical; Archaeology; Biological and medical sciences; Biomarkers - blood; blood; Body; collagen; Diet; discrimination factor; Erythrocytes - chemistry; Feeding. Feeding behavior; Female; Fundamental and applied biological sciences. Psychology; Humans; Individuals; keratin; Male; Middle Aged; Nitrogen Isotopes - analysis; Nitrogen Isotopes - metabolism; nutritional biomarker; Physical anthropology; Prehistoric man; Statistics, Nonparametric; trophic level; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0002-9483; 1096-8644; 2692-7691
• DOI: 10.1002/ajpa.22140

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.