Tell him you feel sorry for him, since he's killing himself with his drug of choice. Offer to have an intervention for him. Tell him if he'll commit to cycling in even for one day, you'll get up earlier, pedal to his house, and then ride in with him. Let him know you're trying to save his life. It might not have any effect on him, but your co-workers will find it hard to argue with the fact that you are healthy and fit, and he's a slob.
Joe