Have you ever considered the fact that by implication, when we thank God for food (if you do), we are also saying that he is responsible for the lack of food in the case of others who are not as fortunate as we are? If you are acknowledging that it is God who is responsible for your physical well-being, and that you don't have plenty because of your own sensibility and hard work, then what about those who are not physically well? What about those who do not have enough to eat? Isn't he responsible for their lack? Can he only take credit for the good, and not the bad if he is in control of these types of things?
If he isn't in control of them, why then give him thanks for food?