Prediction of human dietary δ(15)N intake from standardised food records: validity and precision of single meal and 24-h diet data.

Natural stable isotope ratios (δ(15)N) of humans can be used for nutritional analyses and dietary reconstruction of modern and historic individuals and populations. Information about an individual's metabolic state can be obtained by comparison of tissue and dietary δ(15)N. Different methods have been used to estimate dietary δ(15)N in the past; however, the validity of such predictions has not been compared to experimental values. For a total of 56 meals and 21 samples of 24-h diets, predicted and experimental δ(15)N values were compared. The δ(15)N values were predicted from self-recorded food intake and compared with experimental δ(15)N values. Predicted and experimental δ(15)N values were in good agreement for meals and preparations (r = 0.89, p < .001) as well as for the 24-h diets (r = 0.76, p < .001). Dietary δ(15)N was mainly determined by the amount of fish, whereas the contribution of meat to dietary δ(15)N values was less pronounced. Prediction of human dietary δ(15)N values using standardised food records and representative δ(15)N data sets yields reliable data for dietary δ(15)N intake. A differentiated analysis of the primary protein sources is necessary when relating the proportion of animal-derived protein in the diet by δ(15)N analysis.