Diet studies nitrogen isotopes

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. 

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. 

Nitrogen isotope ratios ( N/ " N) inerease from plants to herbivores to eami-vores and ean be used to estimate the degree of camivory in human diets. Some field studies observe a greater differenee in 5 N between trophie levels in dry, hot habitats than in wet, cool ones. Two hypotheses have been proposed to explain this variation in difference in 8 N between trophic levels. (1) Elevated excretion of -depleted urea in heat/water-stressed animals (2) recycling of nitrogen on protein-deficient diets. Both predict increased diet-tissue 8 N difference under stress. 

Our results do not support the protein stress model. However, this model may apply in cases where stress is intermittent and results in tissue loss, as observed in the study of crows (Hobson and Clark 1992). Low protein levels throughout life after weaning may have produced overall slow and reduced rate of growth rather than tissue loss. Adult rats fed protein-deficient diets after maturation show systematic losses of nitrogen from most tissues that are in proportion to their turnover rates and masses (Uezu et al. 1983). Perhaps tissue nitrogen isotope enrichment may occur under these conditions. New experiments are needed to evaluate this hypothesis. 

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. 

Carbon and nitrogen isotope analyses today are a routine part of the study of human skeletal remains. They are usually calculated along with radiocarbon measurements at dating laboratories. There are other isotopes that may also be of interest in the study of diet such as hydrogen and sulfur, but these are less well understood. 

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. 

As can be expected, plasma proteins have a rapid turnover. Isotopic studies have shown that the half-life of a plasma protein molecule is about 15 days, and that plasma proteins are an important source of proteins in tissues. Animals put on a protein-free diet maintain a perfect nitrogen balance for 3 months when plasma is administered to them. During starvation, plasma proteins remain intact for a long time, in spite of rapid use of tissue proteins. These facts explain the salutary effects of plasma proteins administered for chronic malnutrition, or to surgical patients who cannot be fed. Since there is no correlation between the rate of plasma and tissue protein use in malnutrition, serum protein determination is of little value in estimating a patient s nutritional status. 

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