Abstract In the late medieval period, Holland experienced substantial socio‐economic change. While the region was largely undeveloped prior to 1200 CE, the period after was characterised by extensive urbanisation and flourishing international trade, changes that would have impacted many aspects of life. This paper investigates the effect of these changes on diet by comparing skeletal collections from the early/central medieval rural village of Blokhuizen (800–1200 CE) to the late medieval urban town of Alkmaar (1448–1572 CE) using a combination of the prevalence and location of carious lesions ( n teeth = 3475) and stable carbon and nitrogen isotope data ( n = 50). Results show that the urban Alkmaar population had a significantly higher caries frequency (7.4% vs. 16.1%), starting at a younger age. Moreover, Alkmaar had significantly more approximal caries. These results point to increased consumption of cariogenic products, such as sugars and starches, by the urban citizens. Dietary differences are also demonstrated by the stable isotope data. Alkmaar individuals have significantly enriched δ 15 N ratios and more variable δ 13 C ratios compared with rural Blokhuizen. The elevated δ 15 N values may be due to increased consumption of fish or animals such as omnivorous pigs and chickens. The combination of caries and isotopic data points to clear changes in diet suggesting that urban individuals in the late medieval period had a substantially different diet compared with early rural inhabitants from the same area. Specifically, an increase in market dependence, availability of international trade products, and the growth of commercial fishing in the late medieval period may have contributed to this dietary shift. Future research should include a late medieval rural population to better understand the effects of late medieval socio‐economic developments outside of the urban environment. This study demonstrates that the integration of palaeopathology and stable isotopic research provides a more complete ...