Bread is, in many cultures, the fundamental food, the symbol of all food. And food is communion. Think of it this way: The food we eat is the most tangible exchange we make with our environment. Our food is what most immediately connects us with the reality we inhabit. When you take in food, you temporarily negate the illusion of separation between your body and the rest of existence. Food is a breach of the boundary where we normally perceive separation to begin.
So it is really true, food is communion. It is an affirmation of interconnection and unity with our environment. What we take in becomes, in a very visceral way, a part of us. And we increasingly become composed of it. Remember the common saying, You are what you eat.
Christians understand this literally when taking the communion wafer. Christ tells his followers that, if they don't eat his flesh in the form of the sanctified bread they have no connection with him. He is saying that his essence must be taken into their being in the way that food is taken into the body. Divine substance must be taken in so that it becomes a part of us, and we a part of it. Our thoughts, feelings, our very cells, our total identity must be built of that divine substance -- until finally no boundary is seen between one's individual being and the eternal Being which sustains us. That is holy communion.
I hope it's obvious that you don't have to be a Catholic or a Christian to commune with the Divine in this way. Similar esoteric principles are found, with greater or lesser emphasis, in all world traditions, such as Hindu traditions of prasad. Food is inherently communion with the physical world. It just requires that you peer a little deeper to recognize the more sublime communion, as well.
Something to chew on...