Praying before meals is usually a complete waste of time (it can serve to relieve stress in some people, but that's about it).
First, who actually grew the food? Did God individually grow that food just so you could have it to eat, or did it grow itself to fulfill a biological duty to perpetuate that species? So one should thank the plants and animals that supply the food. Who planted and tended to it, God? When do we write thank-you letters to farmers? And, I suppose we should pray to the bees that help pollinate many of our crops before eating the fruits they help us to have.
As for processing, did God do that? Did God deliver the food? Or, was it a human with a truck that delivered it? Who processed it so we could eat it, God? Who sold us the food and made sure it was available, God? Since when does God own the supermarkets? I, for one, would never shop at a supermarket owned by God, because I would expect the "food" to be outrageously priced.
So God gave you the money to buy the food with? I don't think so. When is the last time God has gone to work instead of you, so you could have the day off and still get paid? I do not remember that ever happening to me, nor have I ever heard of it happening to anyone else. You do the work, and God gets the credit when the companies give you your paycheck--hardly makes sense. As corrupt the government is, there are laws against a company promising a paycheck when a person does the work, and then not delivering. They know they could be shut down and sent to jail if they ever attempted that.
Therefore, it makes no sense at all to actually thank God for our food. The farmers tended to the crops. The crops grew because of biological duty. The bees helped pollinate the food. Various creatures helped protect the crops from pests (including spiders and snakes--who on this board has thought of worshiping spiders and snakes for their part in helping us keep our food safe from pests?). The food is distributed because of companies that are for profit. You got your paycheck because you worked. God did nothing. Hence, He should get nothing.
Yes, it does serve to embarrass people. When you pray about your food in public, everyone else knows you are pious. I have heard that once (from a worldly family thanking Jesus for the food that Jesus did not actually provide). Witlesses usually observe a moment of silence when in public, which also wastes time and serves no purpose.