Isotopic consequences of consumer food choice: Hydrogen and oxygen stable isotope ratios in foods from fast food restaurants versus supermarkets

We investigated geographic trends in the isotopic composition of the modern American diet, purchasing paired food items from fast food restaurants and supermarkets across the USA. We observed large ranges in δ2H and δ18O values, suggesting variation in the region-of-origin for beef, wheat, and potatoes. Mean restaurant meal δ2H and δ18O values (−114 and 22.6‰, respectively) were similar to supermarket values (−111 and 22.1‰, respectively). There were no correlations between restaurant beef and local tap water isotope values but significant correlations between supermarket beef and water (δ2Hbeef = δ2Hwater * 0.19−115‰ and δ18Obeef = δ18Owater * 0.17 + 14.8‰) suggesting regionality in the source of beef available to supermarket patrons. We observed no correlations between the stable isotopic composition of carbohydrates and local tap water. Understanding regional differences observed in some foods but not others will help refine parameters in models used to explore human movements in anthropological, archaeological, and forensic studies.