Diet studies carbon isotopes

The diet of the 19 century residents of Upper Canada was determined from historical sources and was reproduced in order to carry out chemical analysis. Stable carbon isotope analysis of food and human bone demonstrates that the spacing between the food eaten and the bone collagen is around 5.6%o. The value may vary slightly from this estimate since the latter is based on a reconstructed diet and a large number of bone samples, which exhibit a small amount of variation. Nevertheless, this empirically derived result agrees well with estimates from field (Vogel 1978), and laboratory studies (reviewed in Ambrose 1993). 

The mean difference between collagen and flesh (A Nco.f) values for the first sacrificed pairs (91 days after birth) is 0.3 1.09%o while that for third pairs (171 days after birth) is 1.4 0.45%o. This result was unanticipated but seems robust. This indicates the relationship between diet and tissue 8 N and age is complex and varies between tissues. Future studies of diet-tissue nitrogen isotope spacing will have to consider age effects. This contrasts with carbon isotopes (Ambrose and Norr 1993), where we have observed little increase in 8 C with age in the same individuals. 

In addition to the fact that plants differ in their 6 C values, another factor of major importance in nutritional studies is that the carbon isotope ratios of animal tissues and products (e.g., feces or breath CO2) resemble the isotopic composition of animal diets (15-18). Consequently, by analyzing animal tissue, feces, or stomach contents, it is possible to determine whether an animal s diet consists of C3 plants, Ci, plants, or a mixture of both. In ecological studies, the technique is most useful in situations where C3 and Ci, plants coexist, such as in grasslands or deserts. 

An area of human nutrition that promises to benefit from stable carbon isotope techniques is paleonutrition, or the study of past diets. Until recently, methods of studying diets of prehistoric people were based largely on the recovery of fragile and poorly preserved plant and animal... 

Carbon and nitrogen isotopes in archaeology are used primarily in the study of past diet, but there are also important applications that concern past environments and human activity. Carbon and oxygen isotopes have been used in proveniencing to determine the source of marble and other forms of carbonate rocks. Carbon isotopes have been used as survey tool to locate the boundaries of ancient soils and determine the extent of certain types of vegetation. The discussion below focuses on human bone and questions about past diets, the primary application of these two isotopic systems. These principles are also involved in the study of other questions. 

For example, people who eat com have higher ratios of carbon isotopes in their bones. Changes in this isotope ratio in prehistoric bone can indicate when com becomes an important component of the diet. Such studies have been done both in Mexico to ascertain when com was first domesticated and in North America to record when this important staple first arrived. Analysis of carbon isotopes from human bone collagen in Mexico indicates that a heavy dependence on com began around 4500 bc. 

Cerling, T. E. and Harris, J. M, (1999). Carbon isotope fractionation between diet and bioapatite in ungulate mammals and implications for ecological and paleoecological studies. Oecologia 120, 347-363. 

Ericson JE, Sullivan CH, Boaz NT (1981) Diets of Pliocene mammals from Omo, Ethiopia, deduced from carbon isotopic ratios in tooth apatite. Palaeogeog Palaeoclim Palaeoecol 36 69-73 Ericson JE (1985) Strontium isotope characterization in the study of prehistoric human ecology. J Human Evol 14 503-514... 

Stable carbon isotope analysis is particularly useful in New World dietary studies since maize is often the only C4 plant contributing significantly to human diets its contribution to bone collagen and to bone apatite may be estimated by interpolation. Some caution is warranted, however, if succulent plants were present, since they utilize the alternative CAM (crassulacean acid metabolism) photosynthetic pathway which results in carbon isotope ratios similar to those of C4 plants. Nevertheless, CAM plants are unlikely to have been major sources of dietary protein, whether consumed directly or indirectly through herbivorous faunal intermediaries. 

The carbon isotope composition of food ingested by animals is generally reflected in the metabolized products. For example, it is possible to differentiate between animals that have primarily C3 versus C4 diets based on the measurement of the d C value of hair, finger nails, bone collagen, etc. This information is useful in food web studies to determine primary nutrient sources and to discover who is the prey and who the hunter. Nitrogen isotopes are... 

We proposed to study diet and health by combining bone chemistry and histomorphometry. Diet would be determined by analysis of stable isotopes of carbon and nitrogen in bone protein and some preserved hair. In addition, trace elements would be quantitatively analyzed in preserved bone mineral. Abonyi (1993) participated in the study by reconstructing the diet from historical sources and analyzing various foods. Having analyzed human tissues for stable isotopes and trace elements, and foods for the same variables, we hoped to learn more about 19th century diet in southern Ontario, and at the same time, learn more about paleodiet reconstruction. 

Keegan, W.F. and DeNiro, M.J. 1988 Stable carbon- and nitrogen- isotope ratios of bone collagen used to study coral-reef and terrestrial components of prehistoric Bahamian diet. American Antiquity 53 320-336. 

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