So much happens there and how healthy our guts are can dramatically influence how our health is over all. Doctor and author Giulia Enders: "Maybe more interestingly, 90 percent of the nervous fibers that connect gut and brain deliver information from our gut to our brain. And when you think about it a little bit, it does make sense, because our brain is very isolated. It's in this bony skull surrounded by a thick skin, and it needs information to put together a feeling of "How am I, as a whole body, doing?" And the gut, actually, is possibly the most important advisor for the brain because it's our largest sensory organ, collecting information not only on the quality of our nutrients, but really also on how are so many of our immune cells doing, or things like the hormones in our blood that it can sense. And it can package this information, and send it up to the brain."