Prayers over meals originated when Jesus prayed over the fish and the bread that he miraculously multiplied.
That was a miracle to which he called on for holy spirit.
Such miracles don't happen today.
Some say that we thank God because the plants and animals originated with Jehovah's creation, however that was eons ago and an automatic process. That would be like thanking FDR for the FDIC or social security because he originated it rather than the workers today.
Thanks, gratitude, should be shown by what is done by the food, how the energy is used.