Advice on how to handle my boyfriend's eating habits?

Although he is a "big guy" (6 ft. 2 in., 280 lb), he still eats like he's a high school linebacker. He eats large quantities of junk foods, I believe in excess (6 popsicles, 3-5 Twinkies, 2-3 sodas, whole Med. pizza, 2 double burgers in one sitting). I've mentioned things here or there about how I think it's too much, but he either gets really offended or denies it. He is a PE Teacher, so I know he knows about nutrition & health, but I worry because his dad, who was "healthy" by most people's standards, had a heart attack a few years ago and obesity/weight issues run in his family. I love him and his size/eating habits would never be a reason for us to break up, but I don't know how I can tactfully bring my concerns without offending him or hurting his feelings. Help!