Stable isotopes of carbon, nitrogen and hydrogen in the contemporary north American human food web

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Abstract
The use of stable carbon, nitrogen and hydrogen isotopes as dietary markers was investigated in ten healthy subjects living in metropolitan Chicago, USA. Forty foods were isotopically analyzed and compared with human plasma and hair. From isotopic analysis and average U.S. food intake data, the isotopic composition of dietary protein was estimated to be δ13CPDB = ‐18.0‰, δ13NAIR = 5.2‰, and δ2HSMOW = ‐69‰. Dietary lipid was estimated to be δ13C = ‐22.5‰ and dietary carbohydrate to be δ13C = ‐19.6‰. For comparison, the isotopic composition ±SD of plasma protein was δ13C = ‐17.9±0.7‰, δ13N = 9.4±0.5‰, and 2H = ‐57±5‰. Plasma lipid was δ13C = ‐21.6±1.0‰ and plasma carbohydrate was δ13C = ‐19.7±1.9‰. The isotopic composition of nitrogen and hydrogen in hair was similar, δ15N = 9.6±0.5‰ and δ2H=‐62±4‰ respectively, while carbon was slightly enriched in δ13C, 13C = ‐16.6±0.6. The enrichment of 15N in tissue relative to diet probably reflects in vivo isotope fractionation. The diet/tissue differences observed for carbon were small when comparisons were within the same class of macronutrients. The carbon isotope abundance was an accurate predictor of carbon derived from C4 plants.