Dietary reconstruction via stable isotope analysis is an important part of the study of past populations, but can raise issues in many parts of the world where human remains are scarce, absent, or restricted due to ethical concerns. Given these issues, some researchers have used domesticated dogs as human dietary proxies via the Canine Surrogacy Approach (CSA). We performed carbon and nitrogen stable isotope analysis on the hair of 304 humans and 57 dogs from 45 households in two contemporary indigenous communities in Nicaragua’s Bosawas Biosphere Reserve to explore whether dogs function as dietary proxies for their human owners in this Neotropical horticulturalist context. While CSA is broadly viable at these study sites, on a more precise scale the diets of dogs do not reflect the diets of their owners. This raises questions about the applicability of CSA to archaeological contexts, suggesting that relying on dogs as dietary proxies may overlook key variation in past human diets.