It makes no sense to thank God for food, because you got that food yourself. The rebuttal to this is God gave you the means to get the food. He allowed the sun and water to nourish the wheat that would turn into your bread. Yadda yadda. But to thank God for your food is also to assign blame to him for its content. What if it tastes bad? What if there's salmonella or botulism in there? Does that mean God poisoned you?