In the English language, in some contexts, the word "bread" is synonymous with food. In other parts of the world, that's not true. For example, in Eastern Asia, when you say "food," people automatically think of rice. In Malaysia, the same applies to sweet potatoes. For every culture there is a "staff of life." For most it's bread. It's the basic thing you need to stay alive.
But all these words - bread, rice, and sweet potatoes - can also refer to the emotional and spiritual basics that keep us alive. There are a few people without whose love and presence in my life, I would find it difficult, if not impossible, to survive. There's one or two I wouldn't mind getting away from awhile, just to see how I would do without them, but I need most all of them. And without a faith that receives regular nourishment from the Word of God, all of the Word of God, and all of the people of God, I could not survive.
Bread is the biblical metaphor because that was the staple, basic, bottom-line food source of Jesus' day. If Jesus had been from Malaysia, it would have been sweet potatoes, and communion could get a little messy.