| Abstract: |
Presents a series of critical variables- such as elemental metabolism, bone physiology, the relationship between dietary intakes of an element and its concentration in bone, trophic level separation in the foodweb, and diagenetic variability- that must e addressed in the process of theoretical validation. Studies that have employed zinc as a paleodietary indicator fall into three types: 1) empirical approach - they have incorrectly assumed that since zinc tends to be somewhat more abundant in meats and shellfish than in plant foods, a trophic effect is created at various levels of the foodweb that trends in an opposite direction of strontium 2) process of elimination - if zinc levels cannot be attributed to diagenesis, they must be biogenic, and therefore directly reflective of diet or health status. In sufficient attention is paid to zince metabolism, bone physiology, and the relationship between dietary and bone zinc. 3) scientific approach - drawing on the physiology literature to justify the use of zinc Human adults completely remodeling of bone over a period of 7-10 years. Seasonal variability in diet, activity level, and meat consumption are said to contribute to remodeling rate. pg 610 There are 6 conditions that must be met before an element can be considered a valid paleodietary indicator 1) the element \bmust be measurable in bone at levels that exceed contributions likely to occur as a result of postdepositional processes\b 2) deposition in bone must correlate to dietary intakes, and the concentrations of the element in food sources ought to define a trophic-level separation or some other separation according to diet, either through the biopurification of an essential nutrient or through tissue-specific occurence 3) the element should be a bone-seeking element, i.e., one that concentrates in bone, and one that becomes \bincorporated into the hydroxyapatite crystal\b, rather than remain surface bound on the crystal 4) it is advantageous for\b the element \unot\u to be an essential nutrient\b
this way it lacks the tight homeostatic regulation of essential nutrients, the levels of which tend to be fairly constant in bone 5) the element should imitate the movement and activity of an essential nutrient in biological systems, preferably one that concentrates in bone 6) it is advantageous for the element to exhibit low ionic mobility in the geochemical environment
in other words, that it be found in compounds of high molecular stability pg 611 Zinc is an essential mineral and is thus strictly metabolically regulated. pg 613 Phytates affect not the amount of dietary zinc, but the amount absorbed from the diet. pg 614-615 Klepinger (1993:170) concludes her treatment of the experimental studies of rats by stating "[a]though once could argue that the rate is not the ideal animal model for extrapolation to human nutrition, these studies strongly suggest that there is a valid correlation between human dietary Zn to bone Zn. Greater detail regarding the relation between dietary bone zinc, as well as more criteria, such as zinc metabolism and bone physiology, have to be incorporated into the model before it can provide a scientifically sound basis for employing zinc as a paleodietary indicator.
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