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Studying the Diet of the Past

Discover how the study of stable isotopes reveal the diet of ancient people.
Today, archaeology can add a series of very sophisticated analysis to the study of ceramics, and amphora, in order to understand what people ate in different sites and periods. Paleobotanic and archae-zoological evidence sampled in excavations give us clues to the environment and fauna related to the different settlements and their consumption by the local population. This data can be extended today by the analysis of single individuals through the study of the stable isotopes contained in the bones. In the mass spectrometry lab of the Department of Geosciences, we analyze carbon and nitrogen isotopes from individuals by extracting collagen from teeth and bones. These isotopes can be used to study the relative contribution of terrestrial, marine, and freshwater resources to paleodiet.
In fact, we assimilate isotopes through what we eat and drink. And we thus incorporate the isotopic composition of the food into our tissues. When we carry out a stable isotope analysis, it is important to choose the tissues that we can best answer the question we are interested in. For instance, the collagen from the shaft of a long bone or a rib can provide diet information of the last 10, 20 years before the death of the individual. That’s because bone is constantly remodeling. Instead, teeth, once formed cannot remodel anymore. In this way, we can get information on the paleodiet during the formation of the teeth, that means mostly during childhood.
Carbon and nitrogen isotope analysis from collagen of teeth and bones is a powerful tool because it provides direct measures of the human paleodiet. In fact, we use carbon isotope ratio to distinguish between consumers of C3 and C4 plants. In Europe, the majority of the plants uses the C3 photosynthetic pathway and they thus preferentially assimilate the light carbon isotope. Instead, wild C4 plants are rare in Europe and millet sorghum are the only known domesticated C4 plants that can enter in the human paleodiet. Nitrogen isotope ratios are used instead to determine the trophic level of animals and humans, a process of fractionation leads to the enrichment of heavy nitrogen isotope from diet to bone and teeth collagen.
However, the measurement of nitrogen isotope does not permit to distinguish the different animal proteins. So we cannot discriminate the consumption of meat and meat derivatives. Furthermore, the simultaneous analysis of carbon and nitrogen can permit to understand the role of the marine food in the paleodiet. In fact, organism of marine ecosystem at higher values of both carbon and nitrogen isotopes. The comparison of the results of carbon and nitrogen isotopic analysis of late antique and early medieval cemeteries show a multi-faceted situation with a few specific trends emerging locally. In a recent project involving the provinces of Bergamo in Modena in Northern Italy, both antique and early medieval cemeteries were analyzed in order to compare the data chronologically.
The results from human collagen where calibrated and compared with contemporary faunal samples from both areas. The results show regional differences in nutrition. Different systems of subsistence between contemporaneous late antique cemeteries can be observed, possibly relating to poor farm workers, in both cases. At the site sampled in Bergamo, diet was based on C4 plants such as millet and sorghum. In contrast, in the region of Modena, late Roman nutrition was based on wheat, barley, and oats, which are C3 plants, instead. The use of different plants could reflect different economies or different environments which farmers were dependent on.
Two centuries later, the population buried in the same area shows, overall, a terrestrial diet based on C3 plants, which does not seem to be related to a cultural choice, but rather to environmental settings and socioeconomic factors. In total, the comparison with other contemporaneous Italian cemeteries demonstrates the complexity of food crops between the fourth and the eighth centuries. Another way to understand the diet is the study of organic residues. Through gas chromatography analysis, we can shed light on the role of receptacles, the dietary habits of the community that used them, and their cooking methods. In the case of cooking pots, for example, a range of lipid enrichment has been observed in the different parts
of the same vessel: bottom, wall, and rim, depending on the type of cooking method used. For example, when meat or vegetables are boiled some of the fats, oils, and waxes they contain, rises to the surface of the water, making it more likely that they are absorbed into the walls of the cooking vessel. When roasting, however, fats accumulate on the bottom of the vessels while the presence of a cover makes fat absorption more uniform. Even the position of the receptacle in relation to the fire can imply different degrees of absorption. It depends if the pottery was used over an ember, a sort of grill, a flame, or just placed near a heat source to warm the contents.

In this video, we will be speaking with Manuel Rigo and Lara Maritan, professors from the Geosciences Department at the University of Padua who collaborate with archaeologists in the analysis of ancient materials.

Our interview with Manuel will focus on what stable isotopes can reveal about the diet of people living during a certain period. Lara will then discuss gas chromatography analysis, another method of studying ancient diets through the analysis of residues remaining in the walls of ceramics.

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Enlightening the Dark Ages: Early Medieval Archaeology in Italy

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