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Final Activity Report Summary - AAISO (Multi-isotopic analysis as a method for studying the physiology of breastfeeding and weaning in modern and archaeological children)

Stable isotope ratio analysis is an important tool that can be used to elucidate dietary patterns in modern and archaeological humans. This technique is based on the principal that 'you are what you eat' such that the isotopic makeup of body tissues (hair, fingernails, bone, etc) are a direct result of the isotopic composition of the types of foods and liquids consumed. While there have been many applications of stable isotope ratios analysis to understand adult diet, little research has been systematically focused on the discovery and understanding of diet during infancy and childhood.

The focus of this research was to use the bulk protein stable isotope ratios of sulphur, oxygen, hydrogen and the carbon isotopic ratios from amino acids to reveal new information about modern and ancient infant nutrition, specifically breastfeeding and weaning practices. The carbon amino acids provided some of the most important results during breastfeeding and weaning in modern human infants. It was found that there was no difference in the carbon isotopic ratios of breast milk amino acids and amino acids from the foetal period, indicating that there was little or no trophic level fractionation across the placenta. In addition, unique isotopic markers were detected between individuals who were exclusively breastfeeding and those who were undergoing the weaning process. During the weaning process, many of the essential amino acids were depleted by 3 per mil compared to exclusive breastfeeding, and the essential amino acid, threonine, displayed the largest depletion (˜ 7 per mil). This discovery of a large isotopic decrease in carbon for threonine during weaning will be extremely useful to better characterize and identify individuals who were weaning or did not undergo breastfeeding in archaeological populations.

In contrast to the promising isotopic results of the carbon amino acids, the oxygen and hydrogen bulk protein isotopic results did not offer any new information that could not be gleaned from the carbon and nitrogen bulk protein analysis. However, the stable isotope ratio analysis of sulphur in bulk protein did yield some new data that will enhance our understanding of modern and archaeological breastfeeding and weaning patterns. While no unique trophic level fractionation was observed in sulphur isotope ratios during breastfeeding, large isotopic differences corresponding to the weaning foods were found. These sulphur isotopic results were then applied to the late/sub Roman archaeological population of Queenford Farm in the United Kingdom, and it was discovered that this population relied on freshwater protein resources (fish, birds, etc) for the diet during childhood. It should be emphasized that these important dietary patterns could not be detected by the application of only carbon and nitrogen stable isotope ratios, indicating that the multipronged approach of using carbon, nitrogen, and sulphur stable isotopes in conjunction with carbon single amino acid analysis will produce more detailed information about infant and childhood diet. This in turn will be of great interest to individuals who are studying archaeology, bioanthropology, and the history of medicine.

Thus, this work represents the largest and most detailed research on using stable isotope ratios to better characterise and interpret diet during the critical phases of breastfeeding and weaning. The results of this project will not only be of importance to archaeologists, and anthropologists, but will make important contributions to the fields of medicine, forensics, nutrition, and ecology since the application of isotopic techniques is becoming increasingly important in these areas.

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