The creation and expansion of the Mongol Empire during the thirteenth century A.D. brought with it many changes, both for the conquered peoples and for the conquerors themselves. Ruling elite Mongols in foreign lands imposed new customs onto their new subjects, but also adopted some of the characteristics of the cultures they ruled; these are topics of sustained and continuing research interest. Equally interesting but less well researched is what impact the Empire had on Mongols remaining in the Mongolian homeland. Historical sources suggest that the fruits of Empire would have flowed not only to remote Mongol capitals of the Empire but also back to Mongolia proper. Here we use dietary stable isotope analysis to assess whether the Empire brought large changes to the diet of either ruling elites or more common people in the Mongolian homeland. Carbon and nitrogen stable isotope ratios are measured in bone collagen from human and faunal remains from Tavan Tolgoi, a ruling elite cemetery in eastern Mongolia, and compared with ratios from lesser ranked people at the cemetery of Tsagaan chuluut. These are also compared with ratios from the Bronze Age cemetery of Ulaanzuukh, a post-Empire set of human remains, and modern and archaeological human and faunal remains from the wider region. The Tavan Tolgoi isotope ratios do differ from those of Tsagaan chuluut and Ulannzuukh. Comparison with isotope data from the wider region, however, suggests that the differences may be due to differing environmental conditions rather than dietary differences.