Isotope Fractionation: Why Aren't We What We Eat?

The isotopic composition of an element records information about its history. Given a fossil, it is possible to analyse the isotopic composition of the elements in the fossil and to use this to reconstruct the diet that the animal consumed. The process of dietary reconstruction, however, is far from simple. Biological systems are quite complex and can themselves introduce isotopic fractionations that may distort the dietary information. The aim of this paper is to review the concepts of isotope fractionation under steady-state conditions to provide a framework for discussion of dietary reconstruction. Among the elements of interest for dietary reconstruction, nitrogen bears a distinct role. This is because nitrogen is almost unique to protein. A secondary aim of this paper is then to review nitrogen metabolism. The final aim is to combine these in postulating a simple isotopic model of nitrogen metabolism. ? 1999 Academic Press