The smell issuing from either end of a human body, as opposed to a dog's, is less concerned with the material ingested, than the way in which it is digested. Because human and canine digestive systems are quite different, and extract different nutriants depending on the requirements of the host body, the odour of breath or faeces would probably be quite different for each. By the same token, if you feed a dog roast beef and Yorkshire pudding, it's faeces will not smell as a human's would. It sounds like a logical assumption, but biology begs to differ on this one.