Prediction of human dietary δ¹⁵N intake from standardised food records: validity and precision of single meal and 24-h diet data

Natural stable isotope ratios (δ¹⁵N) 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 δ¹⁵N. Different methods have been used to estimate dietary δ¹⁵N 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 δ¹⁵N values were compared. The δ¹⁵N values were predicted from self-recorded food intake and compared with experimental δ¹⁵N values. Predicted and experimental δ¹⁵N 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 δ¹⁵N was mainly determined by the amount of fish, whereas the contribution of meat to dietary δ¹⁵N values was less pronounced. Prediction of human dietary δ¹⁵N values using standardised food records and representative δ¹⁵N data sets yields reliable data for dietary δ¹⁵N intake. A differentiated analysis of the primary protein sources is necessary when relating the proportion of animal-derived protein in the diet by δ¹⁵N analysis.