Stable isotopes and diet: You are what you eat

Archaeologists frequently use many different sources of information to reconstruct ancient diets, including faunal and macrobotanical remains, pollen and phytoliths, as well as pottery residues, coprolites, and indirect sources such as skeletal pathology, dental wear patterns, artistic depictions, and ethnographic observations. In most cases, however, the result is only the determination of the menu, and with the exception of animal foods, without any quantitative estimate of their importance. Furthermore, these data almost always pertain to groups of people and represent a time span of multiple generations if not a century or more. In the late 1970s, though, a new area of dietary research developed based on the isotopic composition of human bone. This work began with the observation that radiocarbon dates on the remains of certain plants such as maize were offset from dates obtained on other remains from the same archaeological context. With the determination that this was due to maize having a different photosynthetic pathway than most plants, which results in a different relative quantity of carbon-14 (and carbon-13) in its tissues, it was realized that carbon isotope ratios in consumer tissues (e.g. bone) would also be affected, and therefore the measurement of carbon isotope ratios could be used to indicate the importance of maize in human diets [1, 2]. Following the observation that nitrogen isotope ratios also vary between different food sources, especially marine vs. terrestrial [3], the stable isotope analysis of human bone quickly became a widely applied technique, especially in areas where isotopically diverse food sources are known to have existed. Analyses of human bone offer the specific advantage relative to faunal and floral