My dog likes to steal bananas and apples from the kitchen countertop. Are they bad for him?

While his brother is pretty much a kibble and water kind of dog, this one will eat just about anything left out on the counter. I put in a little kiddie gate to close off the kitchen, but sometimes I just forget to close it or turn my back for 30 seconds, and he's in and out like a bandit. Usually it is just bread, but I caught him munching a bunch of bananas today, leaving the skins in a neat pile for me. I've seen him eat gs, apples, toothpaste, athlete's foot cream, and a few unmentionables... but bananas? Crazy mutt!