Every good thing we have comes from God, and that is why we offer Grace Before Meals, to acknowledge our dependence on Him and to ask Him to bless us and our food.
We should also offer thanksgiving for the food that we have received by praying the Grace After Meals.
Grace Before Meals
"Bless us, O Lord, and these Thy gifts, which we are about to receive from Thy bounty, through Christ our Lord. Amen."