This is a really fun book and a fairly quick read. The central thesis is that breathing is very important, and over time more and more of us are doing it wrong.
Nestor uses a combination of stories, studies and anecdotes to support his case. Chronologically, he traces us back to our early ancestors and describes changes in their actual face shape that allow them to breathe differently then modern humans. Then, he looks at the different breathing practices in early civilizations and how important they were not just from a cultural standpoint but from a health standpoint. Last, he presents some of the scientific investigations from the last century that have revealed positive health effects for many common conditions not just respiratory but neurologic, circulatory, psychiatric.
One of the fun parts about this book is that he investigates a lot of these techniques personally, visiting several gurus mentioned in the book and uses these approaches as a guinea pig to fix some of his own problems.
My main take away from this book may be a little biased--this all seemed very osteopathic to me. One of the core tenants of osteopathy is that the body is container and then all of its parts are related; dysfunction of one system will have negative effects on other systems. I thought he did a good job of conveying that breathing is not just a breath. Breathing is made up of the muscles, the skeleton and rib cage and diaphragm working with the gas exchange of the lungs and blood flow to those organs, all of which can activate the nervous system to send back information to the brain, which can then send forth a cascade of hormones which have varying affects.
What does this mean for you? One of his most tangible points from the book is that the perfect breath is a rhythm of 5.5 breaths per minute (focusing on breathing through the nose!) This is a 5.5 second inhale and a 5.5 second exhale. There are lots of other things you can do, but if you find yourself feeling a certain type of way, try restoring your breathing rhythm to this cadence.