I don't think so...Of course it's better if she/he eats only her own food, but I don't think there is anything in the catfood itself that would be injurous. Not just the best thing for them. I have read in several books that cats are the only true carnivores left, (they NEED meat/products to survive) so there food is very high in protein compared to dogs. My Cody LOVES my cats' food and will steal their bowl and run away with it any chance she gets. She actually watches when I leave the room then starts circling the counter if I forgot to remove their dish! Catfood breath bigtime! Maybe some others have some greater insight into this!