When you start reading Patrick McKeown’s new book, you might wonder if it’s a joke: “The biggest obstacle to your health and fitness is a rarely identified problem: ‘chronic overbreathing,’ ” which, he tells us, “contributes to many ailments including anxiety, asthma, fatigue, insomnia, heart problems and even obesity.”

Seriously? We’re sick and tired because we’re breathing too much?

The Oxygen Advantage: The Simple, Scientifically Proven Breathing Techniques for a Healthier, Slimmer, Faster, and Fitter You” — a title so long you might need to take a breath in the middle — is indeed serious.

As McKeown sees it, when our red blood cells are saturated with oxygen, it is carbon dioxide — which most of us think of as just the stuff we exhale — that is “the key variable that allows the release of oxygen from the red blood cells to be metabolized by the body.” And when we overbreathe, he says, “we exhale too much carbon dioxide, leaving our body literally gasping for oxygen.”

This theory is based on the work of Konstantin Buteyko, a Russian doctor with the Soviet-era space program, whose techniques, particularly for treating asthma, have gotten some attention in this country. McKeown, who studied under Buteyko, suggests in his book that people try something like high-altitude training — learning to hold your breath for increasing lengths of time, taking shallow breaths, activating the diaphragm for better breath control and even taping your mouth closed at night to force yourself to breathe through your nose while you’re sleeping.

That might sound odd. But it’s worth noting that yoga teachers and meditation practitioners have long preached the benefits of controlled slow breathing. And this doesn’t present the danger of, say, using alternative medicines that haven’t been thoroughly tested.

But note: McKeown warns that his techniques should not be used by pregnant women and that people with high blood pressure, cancer or a few other ailments should stick with his gentlest recommendations.

Caveat, breather.