Is it healthy to feed a cat human food?

I dont want him to eat human food at all but my grandmother gives my kitten human food behind my back. I just caught her doing so. He eats cat food too. He does not beg for human food but my grandmother calls for him, he comes, and thinking its to play or something and she feeds him human food instead. She does it to her cats and shes trying to do the same to mine! She does not listen to my request to not feed him human food either. Help? Suggestions? And answer. Please?