My 12 year old son entered Jr. High this year at 5'9" tall and weighing 180 lbs. The boy eats like a Hobbit, every hour on the hour is good for him. When we do go out to eat, we visit buffets because he can pack away 5 full plates of food, still have room for dessert, and is hungry again in an hour. He's built like my husband; tall, broad, and strapping with muscle.
850 calories for him is a snack.
I dare some food Nazi to come between him and his home-made lunch. Fighting the "establishment" is a sharply honed talent of mine.