Sorry to hear you are having trouble.

For his age, the punishment seems a bit long, and perhaps that might be contributing to the repeated untruthfulness.

I was told by a professional that my ten-year old should be given an assignment plus loose something just for a day.

In terms of what to take away it should be something they care about, for example computer time, x-box, cartoons. In terms of an assignment it could be write a sentence x-number of times, an extra chore, or have them help you with a chore.

Another thing to think about... Taking food away from small children may lead to hoarding or hiding food especially with anxious prone children.

BTW I'm waiting for my copy of the Nurtured Heart.