How can I stop my hermit from eating to much?

The deal is when i first got them I began to feed them hermit food (the pebbles). But then we started feeding them lettuce, apples and carrots. They loved that! But I think i might be feeding them too much each day. I change the food before school, when I get home, and my dad feeds them during the day when I can not feed them, i also feed them exactly before I go to bed. Is that to frequent?