My 14 Year Old Grandson, Weighs About 200lbs. He Is

My 14 year old grandson, weighs about 200lbs. He is semi active. But I find he has a bad eating habits. If I buy something and he happens to like it, he will eat it all. Regardless that their are others in the house. Ex: I rarely buy very fattening things. Once in awhile I treat us and buy something special. Yesterday I bought 4 large lady locks in a container. Yesterday he ate two of them, today he ate the other 2. He always do this when no one is looking or no one is home. This is just one example.