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The diet-body offset in human nitrogen isotopic values: a controlled dietary study.
T C O'Connell1, C J Kneale, N Tasevska
1Department of Archaeology and Anthropology, University of Cambridge, UK. tco21@cam.ac.uk
American Journal of Physical Anthropology
|October 9, 2012
Summary
Nitrogen isotope analysis reveals the diet-body trophic enrichment in humans. This study precisely measured the nitrogen isotope spacing (Δ(15)N) in red blood cells, keratin, and collagen, offering new insights into prehistoric diet reconstructions.
Area of Science:
- Paleoecology
- Biogeochemistry
- Human Evolution
Background:
- Trophic level enrichment causes nitrogen isotopic values to increase up the food chain.
- Quantifying the diet-body nitrogen isotope spacing (Δ(15)N) is challenging, especially for humans.
- Previous studies often assumed a Δ(15)N spacing of +3-5‰ in archaeological literature.
Purpose of the Study:
- To provide the first human data on isotopically known diets, comparing dietary intake with body tissue (red blood cells).
- To accurately measure the diet-red blood cell Δ(15)N spacing.
- To estimate human Δ(15)N spacing for other tissues like keratin and collagen for improved paleodietary studies.
Main Methods:
- Controlled feeding study with 11 human subjects over 30 days.
- Diets were customized to match individual habitual intake to minimize short-term dietary fluctuations.
- Nitrogen isotope ratios (δ(15)N) were measured in dietary intake and red blood cell samples.
Main Results:
- The measured diet-red blood cell Δ(15)N spacing was +3.5‰.
- Estimated human Δ(15)N spacing for diet-keratin was +5.0–5.3‰, aligning with existing studies.
- Estimated human Δ(15)N spacing for diet-collagen was approximately +6‰.
Conclusions:
- The measured Δ(15)N(diet-RBC) of +3.5‰ provides a precise value for human red blood cells.
- The higher estimated Δ(15)N(diet-collagen) of ~6‰ suggests potential overestimation of animal protein in prehistoric human diets in previous isotopic studies.
- These findings refine the application of nitrogen isotope analysis in paleodietary research.
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