This Amish Table Prayer is an interesting prayer for moderation in using our blessings.  The sentiments are very relevant to use as table blessing when dieting or fasting.

Enable us to use Thy manifold
blessings with moderation;

Grant our hearts wisdom to avoid
excess in eating and drinking
and in the cares of this life;

Teach us to put our trust in Thee
and to await Thy helping hand.