The big thing is carbohydrate counting so get a carb book. If he takes Humalog insulin, dose would be
1 unit per 10 grams
carb. If not, you must watch the simple sugars carefully. Small amounts of fruit are okay and larger amounts can be tolerated after eating protein. However, if he is exercising, then he can get away with eating something like a whole fruit right before exercising (depending on his glucose level) beforehand and the cardio exercise will even it out.