So, what if there were a game where instead of collecting candy, Keen fought it? It could be like that Dreams mod I made, some sort of sequel to Keen fighting veget-
He compensates that by using his ability to jump so high. I mean jumping so higher would require an astonishing amount of energy, and by doing just jumping he burns fats like crazy. And besides, he is young and his metabolism works like crazy anyway so he can deal with icecreams and sandwiches.