My 1 year old Siberian husky seems to be on the slimmer side even though hes extremely healthy and playfull.?

I have a one year old male Siberian husky and he gets plenty of excersize and plays a lot and eats a hell of a lot but no matter what he seems to be skinny. Is their any ideas on how to maybe naturally bulk him up a little? I was thinking maybe he could possibly have some tape worms and I'm going to get him checked out for that but thats doubtfull. Well just let me know if you have any nutritional ideas you could give me. Also he eats Purina dog food.