Dietary evaluation using isotopic analyses of carbon in collagen from bone is an exciting new area of archaeological chemistry.Analyses of bone from herbivores, carnivores, and omnivores (including humans) suggest that a simple isotopic fractionation between dietary carbon and carbon in bone collagen may be an inadequate model for interpretation of results. Dietary carbohydrates are primarily metabolized for energy and their carbon is reflected mainly in the hydroxyapatite of bone. Dietary lipids are also important energy components of the diet.Dietary proteins, on the other hand, are utilized for protein (e.g. bone collagen) synthesis as needed and only excess amino acids are metabolized for energy. Herbivores, carnivores, and omnivores thus might have different isotopic fractionation models, each of which is presented.Biochemical evidence in support of these models is discussed. Isotopic studies relating to nutrition and diet have originated from two diverse fields, bio-medical research and archaeology. Numerous studies have been reported by researchers in the areas of biochemistryand medicine, using either isotopically enriched compounds or the natural variations in isotopic abundances. Such studies usually involve a specific chemical as a tracer of biochemical pathways, and in these studies soft tissues or body fluids are analyzed.Recent work in nutrition has begun to examine the isotopic composition of carbon in macronu trient s in diets and their disposition in body tissues (1.2). The isotopic composition of hard tissue (i.e., bone), however, has been largely ignored in biochemical studies.Archaeologists are often interested in dietary considerations, but normally have only bone to represent the human organism, the soft tissues having decomposed. Dietary reconstruction using

Proportions of marine vs. terrestrial resources in prehistoric human diets in the southern Mariana Islands (Guam, Rota, Saipan), Micronesia, have been estimated by analysis of stable isotope ratios of carbon and nitrogen in bone collagen and of carbon in apatite. The isotopic composition of marine and terrestrial food resources from the Marianas have also been determined. Experimental evidence shows that collagen carbon isotopes mainly reflect those of dietary protein sources and thus overestimate the contribution of marine animal foods. Marine protein consumption apparently ranges from approximately 20% to approximately 50% on these islands. Experiments also demonstrate the carbon isotope ratio of bone apatite carbonate accurately reflects that of the whole diet. Carbonate carbon isotope data suggest some individuals consumed significant amounts of 13C-enriched (C4) plants or seaweeds. Sugar cane is an indigenous C4 crop and seaweeds are eaten throughout the Pacific, but they have not been considered by archaeologists to have been prehistoric dietary staples. Apatite carbon isotope analysis has apparently identified previously unrecognized prehistoric dietary adaptations in the Mariana Islands, but this must be confirmed by archaeobotanical evidence.

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