During a seven-day experiment, the natural diets of dogs (commercial dog chow; blue) and wolves (carcasses; orange) were swapped, and their gut microbiomes measured at the end of the experiment. The gut microbiomes of control samples of dogs and wolves that were fed their natural diets were also measured. At the end of the experiment, the microbiomes of wolves eating dog chow more closely resembled the microbiomes of dogs than the microbiomes of wolves eating their natural diet. An even stronger effect was observed for dogs. This could be due to the microbiomes of dogs being more plastic as a result of consuming a variable omnivorous diet, whereas wolves have a narrower carnivorous diet.