| Summary: | Tooth wear, caries, and alveolar modifications provide the most common and most informative evidence regarding the nutritional condition of past populations. However, the development of biochemical techniques such as the analysis of stable isotopes and trace elements now offers new perspectives for this research. The analysis of stable isotopes enables us to determine what types of food were consumed during an individual’s life. Based on analyses of the stable isotopes of nitrogen (15N/14N) and carbon (13C/12C) in bone and tooth collagen, this study reconstructs the dietary behaviour of a historical population excavated in the cemetery of the church of Saint- Laurent at Grenoble. This research evaluates the changes in dietary behaviour not only within the population, but also over the life span of individuals. An additional objective is to analyze the data according to different biological, archaeological and chronological criteria. The archaeological site of Saint-Laurent is located in Isère, France, in the Northern Alps, in a suburb of the city of Grenoble. The osteoarchaeological material consists of 336 individuals, from which 55 were chosen for isotope analyses. There are 34 adults and 21 sub-adults divided into three burial phases—phase 13, phase 14, and phase 15— representing the late medieval period, from the 13th to the 15th centuries AD. Isotope analyses were carried out on both human and animal bones, to evaluate the relationship between the environment and the individuals from Saint-Laurent. Two main dietary trends have been detected, one mainly vegetarian and the other based upon meat and dairy products. The consumption of fish, although not to be dismissed, does not appear to be significant. Although the samples were small, the data indicate an increase in protein consumption between the 14th and 15th centuries, which may correlate with greater longevity and taller stature; the individuals buried in the cloister may have had access to a diet richer in animal protein than those buried in the church square. An exclusively vegetarian diet, known from historical studies to be common for the rural populations of this period, has not been observed for the Saint-Laurent population. In order to observe dietary changes within an individual’s life span, a sampling strategy requiring analysis of three tissues from a skeleton was used. Because of differential bone and dental growth, it is possible to isolate isotope signals corresponding to specific points in an individual’s life. Thus dietary changes related to breastfeeding and weaning periods were studied because maternal milk induces an increase in nitrogen-15 within the developing tissues of babies. Three kinds of tissues per individual were sampled: a growing tooth root, corresponding to a diet signal at the time of death, and two pieces of mandibular bone—one close to a tooth bud and the second close to an erupted tooth - both corresponding to different diet signals prior to the time of death. Isotope data indicates that weaning began between 2.6 and 3.3 years for the children in the medieval Saint-Laurent population. The application of this strategy for children aged between 5-11 years of age has indicated another phenomenon, an enrichment in nitrogen-15 at the time of death, most likely due to an unidentified source of stress. The above data support evidence for economic, political and environmental changes occurring at the end of the medieval period in the Saint-Laurent population. A wide dispersion of isotope signals in the 14th century diet indicates access to a wider variety of food resources. This diversity could also indicate different means of subsistence induced by historical events such as the Hundred Years’War and the plagues of the mid-14th century AD. The increased consumption of animal protein between the 14th and 15th centuries, as well as a reduction in dietary diversity in the 15th century could indicate a period of greater economic stability with more uniform conditions characterizing a urban food economy. Despite the implication of a general increase in socio-economic stability, there is also the possibility that the individuals buried in the cloister of the church of Saint-Laurent were of a higher social level than those buried in the church square.
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