5.2 Dietary Isotope Analysis

This lesson introduces dietary isotope analysis in archaeology, a scientific method that examines elemental isotopes in animal tissue by measuring ratios between isotopes of the same element. Carbon and nitrogen are the primary elements used. Here the focus is on human diet, though the method is equally valuable for studying animals such as dogs and pigs.

Food and Elements

All of the food we eat is made up of complex elemental compounds, and all foods contain various amounts of carbon and nitrogen. Carbon and nitrogen are integral to various biological compounds such as fats, carbohydrates, and amino acids. As a result, the food we eat transfers external carbon and nitrogen from the food to be used in our bodies. These elements are used to make our own fats, carbohydrates, and amino acids - and some of them are laid down in our hard tissueThe mineralised tissues in the body, such as bone, enamel, cementum, and dentine, which survive in the archaeological record.. This means that elements from the food we eat literally become part of our skeletal structure. These elements are not monolithic, and can have numerous isotopes. Isotopes are slightly different forms of the same element that contain the same number of protons in the nucleus, and thus share the same atomic number. They also share the same number of electrons provided they do not become ionisedWhen an atom or molecule gains or loses electrons, acquiring a charge..

However, different isotopes have various amounts of neutrons - which will subtly but notably impact their mass, mass-to-charge ratio, and their behaviour in biological and natural systems. Ultimately this means that elements, and different isotopes of elements, get incorporated into biological tissue that archaeologists can analyse and measure to try and shed light onto the origin of those isotopes. We can analyse these elements with a method called mass spectrometryA technique used to measure the relative abundance of different isotopes in a sample., that effectively measures the relative amounts of different isotopes of the same elements. Different food types, sources, and anthropogenicResulting from human activity, often used to describe environmental or isotopic changes influenced by humans. processes can impact the amount of different elemental isotopes in our food - and as such the ratio of isotopes of the same element can provide information about diet in the past.