A STABLE ISOTOPE STUDY OF THE DIETS OF UTAH VALLEY UNIVERSITY COMMUNITY MEMBERS

To investigate the diets of Utah Valley University (UVU) community members, we analyzed the bulk carbon and nitrogen stable isotope composition of hair samples from seventy-three randomly selected participants (UVU students, faculty, and staff). These participants also self-reported average weekly intake of staples like meat, fish, wheat, vegetables, dairy products, and corn. With respect to carbon isotopes, C3 and C4 plants discriminate ¹³C differently. As a result, hair δ¹³C increases with the proportion of C4 plant consumed directly by the individuals or by the livestock they ate. δ¹⁵N increases by ~4‰ per trophic level and may also be controlled by agricultural practices such as the widespread use of artificial fertilizers, which are enriched in ¹⁵N relative to animal-derived manure. The climate in the food source area, physiological factors, and health conditions may affect both isotopes to a lesser extent, particularly nitrogen. Enrichments of ~3‰ (in δ¹³C) and ~4‰ (in δ¹⁵N) are expected between diet and hair. Average (±1 sd) δ¹³C (vs. PDB) and δ¹⁵N (vs. AIR) values for the UVU community are -17.88±0.73‰ and 8.82±0.45‰, respectively. These values are indistinguishable from the average δ¹³C and δ¹⁵N of the whole US population. A calculation based on a mass balance equation suggest that the percentage of C4 plants (mainly corn) in the diet of these participants and/or in the livestock they ate is ~46%. Average values for males (δ¹³C=-17.65±0.76; δ¹⁵N=8.94±0.39) are indistinguishable from those of females (δ¹³C=-18.00±0.68; δ¹⁵N=8.77±0.42). No correlations are observed based on subjects’ age and between self-reported diet and isotopic values, suggesting wrong self-perceptions in dietary habits. Finally, all participants are similar in δ¹³C and δ¹⁵N, suggesting food production globalization and dietary homogeneity among the investigated UVU community members.