| Summary: | Stable isotope ratios, such as δ 15 N, of tissues reflect the isotopic pattern of food sources. Animal nitrogen has a higher isotope ratio than nitrogen derived from plant sources, because δ 15 N accumulates up the food chain. The objective of this study was to determine whether the δ 15 N stable isotope ratio is associated with self‐reported dietary animal protein intake (animal versus vegetable). We hypothesized δ 15 N would be associated with animal, particularly fish, intake in this population of Yup'ik Eskimos. We examined the relation between red blood cell (RBC) stable isotope ratios and self‐reported animal protein intake derived from four 24‐hour dietary recalls in a community‐based sample of 70 Yup'ik Eskimos. RBC δ 15 N was strongly correlated with proportion of protein intake from animal sources (r = 0.71). The results support the utility of RBC δ 15 N as a biomarker of proportion of protein intake from animal sources. Controlled feeding studies to evaluate the validity of stable isotope ratios as a method to assess dietary protein source in epidemiologic studies are warranted. This research was supported by the Institute for Translational Health Sciences Visiting Scholars Program, NIH NCRR (P20 RR16430‐10) and NIH NIDDK R01DK07442.
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