Calculation of total meal δ13C from individual food δ13C (813.2)

Abstract

Variations in the isotopic signature of carbon in biological samples can be used to distinguish dietary patterns and monitor shifts in metabolism. But for these variations to have meaning, the isotopic signature of the diet must be known. We sought to determine if knowledge of the 13C isotopic abundance (δ13C) of individual foods can be used to reliably calculate the δ13C of a mixed meal. Aliquots of 60 individual foods and 21 meals comprised of those foods were freeze‐dried, ground, weighed, and analyzed using an isotope ratio mass spectrometer. The δ13C of the individual foods were then used to calculate the δ13C of meals comprised of those foods and compared to the analyzed δ13C of the corresponding meal. The calculation was weighted such that the contribution of individual foods to the isotopic signature of the meal was relative to the caloric contribution of the food item to the total caloric content of the meal. The measured δ13C (‐23.76‰) and calculated δ13C (‐23.72‰) of the meals did not differ (‐0.04‰, 95% CI = ‐0.30 to 0.22‰) with limits of agreement (+/‐ 2SD) of ‐1.20 ‐ 1.12‰, and the difference was not dependent upon the magnitude of the δ13C by Bland‐Altman regression (slope = ‐0.17, p = 0.88). In conclusion, approximation of the isotopic signature of whole meals can easily and accurately be calculated when the analysis of each meal is not feasible. These results will aid in the characterization of individual dietary intake.Grant Funding Source: Supported by he United State Department of Agriculture, Agricultural Research Service