Cat has gas, diarrhea, and is licking the fur off his belly. Is it his food?

My 8 yr old male cat has been licking the fur off of his belly and the inside of his back legs. There is nosing of bites or skin irritation. He also has gas and bad-smelling diarrhea. Otherwise he is healthy and happy. My other two cats have no problems. I feed them Iams dry and Fancy Feast Gravy once a day. Could it be a food allergy?

Yes or many other things. You need to have your cat examined by a vet to make sure. The diarrhea should be a big concern.