Studying archaeological foodways using stable isotope analysis can provide insights into the social, ecological, and environmental conditions that past communities experienced. Traces of the food a person consumed and the water that they imbibed during life are preserved in their bones and teeth after death, making it possible to reconstruct diet and region of residency through isotopic analyses of archaeological skeletal remains. This research focuses on burials from the archaeological sites of Phu Noi and Tha Kae in central Thailand, excavated by the Thai-Italian Lopburi Regional Archaeological Project (LoRAP). Radiogenic strontium and stable carbon, nitrogen, and oxygen isotope analysis of multiple chronological tissues from archaeological individuals enabled this research to assess diet and changes in regional residence across individual lifetimes, from early childhood through adolescence and adulthood. The results document dietary and environmental differences between individuals from both sites, with those from Phu Noi exhibiting higher δ13C values, lower δ15N, and lower δ18O values compared to individuals from Tha Kae. We examine the numerous cultural, dietary, ecological, and environmental factors that may explain these observations in the context of broader environmental trends and changes in foodways that occurred over the course of the Metal Age. At regional scales, the results suggest that subsistence systems in Metal Age central Thailand were distinctive from those previously observed in coastal and northeast Thailand, with variation across chronological time and geographic space. The results provide further evidence of flexible and resilient subsistence systems in central Thailand that were well adapted to the region’s highly variable rainfall, incorporating small to moderate quantities of drought-resistant C4 plants, presumably millet, and a wide array of other cultivated and wild plant foods, freshwater fish and invertebrates, and terrestrial herbivores.