Choice of dietary protein of vegetarians and omnivores is reflected in their hair protein C-13 and N-15 abundance

Stable isotopic (N-15, C-13) composition of tissues depends on isotopic pattern of food sources. We investigated whether the isotopic compositions of human hair protein and amino acids reflect the habitual dietary protein intake. Hair samples were analyzed from 100 omnivores (selected randomly out of the 1987-1988 German nutrition survey VERA), and from 15 ovo-lacto-vegetarians (OLV), and from 6 vegans recruited separately. Hair bulk and amino acid specific isotopic compositions were analyzed by isotope-ratio mass spectrometry (EA/IRMS and GC/C/IRMS, respectively) and the results were correlated with data of the 7 day dietary records. Hair bulk N-15 and C-13 abundances clearly reflect the particular eating habits. Vegans can be distinguished from OLV and both are significantly distinct from omnivores in both N-15 and C-13 abundances. N-15 and C-13 abundances rose with a higher proportion of animal to total protein intake (PAPI). Individual proportions of animal protein consumption OPAP) were calculated using isotopic abundances and a linear regression model using animal protein consumption data of vegans (PAPI = 0) and omnivores (mean PAPI = 0.639). IPAP values positively correlated with the intake of protein, meat, meat products, and animal protein. Distinct patterns for hair amino acid specific N-15 and C-13 abundances were measured but with lower resolution between food preference groups compared with bulk values. In conclusion, hair C-13 and N-15 values both reflected the extent of animal protein consumption. Bulk isotopic abundance of hair can be tested for future use in the validation of dietary assessment methods. Copyright © 2005 John Wiley & Sons, Ltd.