Why you aren’t always what you eat: Exploring the influence of dietary macro-nutrient composition on diet-tissue 15N-enrichment and the implications for palaeodietary reconstruction.

The stable isotope analysis of preserved human and animal tissues is a major methodological approach employed by archaeological scientists for the reconstruction of past diets. Since initial applications more than 30 years ago, these approaches – particularly the stable carbon and nitrogen isotope analysis of extracted bone collagen – have made significant contributions to our understanding of the past, from characterising the dietary changes surrounding the ‘Neolithic Revolution’ to the reconstructing of the dietary habits of our extinct ancestors (see Britton 2017 for overview). Originally stemming from advances in the plant sciences, biology and ecology, the application of these techniques to archaeological materials relies on fundamental data from modern experimental and field studies. For example, nitrogen isotope analysis of preserved bodily proteins – such as bone collagen or hair keratin – is commonly used to reconstruct the source of protein most commonly consumed. This is underpinned by the ‘trophic level effect’ – the stepwise enrichment of 15N up the food chain by ~3-5 ‰ with every step, which is observable in simple modern foodwebs (e.g. Bocherens and Drucker 2003).

However, human foodwebs are rarely simple and, as complex-tool using social omnivores, humans are capable of subsisting on very diverse diets with varying macro-nutrient contents. The interpretation of human dietary data at climatic or latitudinal extremes in particular necessitate a more nuanced understanding of nitrogen isotope systematics. Further controlled feeding experiments are required to better understand the relationship between dietary macro-nutrient composition and diet-tissue 15N-enrichment for archaeologists to be able to better interpret the data generated from archaeological bone proteins.

This inter-disciplinary studentship will undertake primary research into the impact of dietary macro-nutrient composition on diet-tissue enrichment, including the collating and re-evaluating of data from the archaeological and clinical/ecological literature, and the generation of new experimental data from controlled feeding experiments. The (mouse-based) controlled feeding experiment (School of Biological Sciences, Aberdeen) will involve the manipulation of dietary macro-nutrient composition (% protein, % fat and % carbohydrates), coupled with the eventual sampling of archaeologically-relevant tissues, such as bone collagen. The empirical data produced from this study will allow the relationship between dietary-macro-nutrient composition and diet-tissue 15N-enrichment to be directly assessed in an omnivore. These data will provide vital ground-truthing for the application of these approaches to the study of ancient human diet, particularly at climatic or latitudinal extremes where carbohydrate-rich plants may be scarce, and will have a direct impact on the interpretation of previously-published and newly-generated archaeological palaeodietary data.

The student will be expected to contribute to the design of the feeding experiment and conduct tissue sample collection. Full training will be given to the student in this, and also in the preparation of biological samples ahead of stable isotope analysis and in sample analysis via mass spectrometry. The student will be guided through the biological, nutritional, isotopic and archaeological literature by respective specialists in the field (Prof. John Speakman, Dr. Catherine Hambly and Dr. Kate Britton).

Candidates should hold or expect to hold, by the time of the project start date, a very good honours degree (at least a 2.1 or equivalent) and/or a Masters degree in a relevant subject (e.g. Archaeological Science, Chemistry, Biology, Nutritional Science, etc.), and have a strong background in either the earth sciences, biological sciences, or biomolecular archaeology. Past experience with stable isotope analysis and mass spectrometry is desirable, but not essential.