The Science Of Yoga: The Risks And The Rewards

In his book The Science of Yoga: The Risks and the Rewards, New York Times science writer and long-time yoga practitioner William Broad investigates popular health claims about yoga—that it boosts metabolism, for example—and finds that scientific studies tell a different story.

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JOHN DANKOSKY, HOST:

This is SCIENCE FRIDAY. I'm John Dankosky, in for Ira. Twenty million people practice yoga in the United States. You might be one of them. I know I should practice way more than I do. But why do you do it? To relax, maybe to get in shape? Yoga is often advertised as having the same aerobic punch as a jog or maybe a few laps on the elliptical, a way to rev-up your metabolism, even help you maybe lose weight.

But how true is that? Does science support any of these claims? As our next guest found out, oftentimes the answer is, well, no. He debunks some of the mythology of what call the - what some call the yoga industrial complex in his book "The Science of Yoga: The Risks and the Rewards."

But don't roll up your mat just yet. Take a deep, cleansing breath. It's not all bad news. We'll talk about some ways that yoga actually does benefit the body and the mind.

William Broad is the author of "The Science of Yoga: The Risks and the Rewards." He's also a science writer at the New York Times, a longtime yoga practitioner himself. He joins us in our New York studios today. Welcome back to SCIENCE FRIDAY.

WILLIAM BROAD: Thank you, John.

DANKOSKY: So first of all, you've been practicing for a very long time yourself, how long?

BROAD: Oh, gosh, centuries, right?

(SOUNDBITE OF LAUGHTER)

BROAD: No, since 1970.

DANKOSKY: Since 1970. When did the big yoga boom happen in the United States?

BROAD: I think it was back then sometime, right. It rolled out of the '60s, and people, you know, the peace and love generation got into it, and I found it, too. And I fell in love with it. It did great things, right. It helped me relax. It helped me feel better in body and mind, and I got hooked.

DANKOSKY: But it's changed a lot since then, right? It's a lot of things, it's not certainly just one thing, and 20 million practicing something they call yoga is an awful lot of people.

BROAD: Yeah, it's gone through all kinds of transformations. In the front of my book, I try to go through a list of some of the major styles. But in some respects, it's gotten very athletic, very competitive. There are styles that - you know, power yoga, where you're out there, you know, supposed to be sweating bullets and pumping the heart and doing all that good cardio stuff that all the presidential panels and the health officials want you to do.

So there - it's really proliferated into a - probably for the beginner a confusing array of a zillion different styles.

DANKOSKY: If you do yoga, we'd love to hear from you, 1-800-989-8255, 1-800-989-TALK, if you have questions about the science of yoga - so let's go through these health claims. Boosting metabolism, that I mentioned, is a big one. Some people think that they're going to go practice yoga, and they're going to get that metabolic boost that maybe some sort of aerobic exercise will give you. What do you say? What did you find out?

BROAD: The science - it's interesting because the science in yoga is sketchy. Some parts are better than others. But this part is dispositive. It's so clear. And the answer is that if yoga does one thing, it slows you down. It relaxes you.

And that means your overall metabolic rate tends to go down. You get this kind of inner flexibility that mirrors the outer flexibility that you get, right. Well, all things being equal, if your metabolism is going down, and you eat the same number of calories, right, you are going to gain weight.

So presto, chango(ph) , new layers of fat that get added because you're yoga, because you're learning how to relax more. Now it's more complicated than that because yoga also helps you gain different kinds of discipline. It can break the stress eating cycle, right. Those are psychological things.

And I'd say on balance, most yoga teachers tend to be lithe rather than lumpy, right, they have somehow mastered - well, they also burn up a lot of calories if they're teaching four or five classes a day or whatever. But, you know, it can teach you all kinds of psychological tricks that will help you lose weight.

But, you know, that happens despite what's going on with your metabolism, not because of it. So many books talk about zipping it up. That's just - there's no science to support that.

DANKOSKY: But there has to be a different metabolic effect depending on the type of yoga you're doing, and that's one of the things that's interesting about your book. Because this idea of yoga has changed so much, and there's so many different types of classes on can take or types of yoga that one can practice, the sweaty yoga that seems more like a gym class, I mean, can you really say that that is something that's going to slow your metabolism down? Is it still yoga?

BROAD: Ultimately, I mean, you can - they've done studies on the fast stuff, you know, Ashtanga-based and highly flow-oriented stuff, and it doesn't, you know, do those aerobic things, but overall, all the styles induce this kind of physiological relaxation that lowers your rate.

There was a beautiful study done in India in 2006, and they measured, very carefully, the decrease in the metabolic level. Women are more gifted than men, as it turns, 18 percent overall lowering versus eight percent for the men in the study.

So it's beautifully quantified, and you see it over a century and a half. Like the very first study, in 1851, the guy who first started looking at yogis, looking at yogis through a scientific lens, he - his synonym for yoga was human hibernation.

You know, what's the secret? How do these guys all do it? And what they were doing was slowing themselves down, reducing their metabolism. So there's a long, long history of these kind of studies.

DANKOSKY: And is that through the breathing, the movements?

BROAD: It's the whole package, right. I mean, there's this synergism between, among all these things. And what it's doing is inducing this inner physiological flexibility, right, that allows you to lapse into a - like an electron, you know, going down into a lower state of excitation. That tends to happen with people, too.

It's also why I think people love yoga, right. They don't - you know, yoga isn't big in urban centers and really crazy, you know, aspects of our cities because it is zipping you up, it's doing just the opposite. It's slowing you down. It's helping you relax and de-stress.

DANKOSKY: What about this idea that yoga breathing gets more oxygen into the blood because of this special breathing technique?

BROAD: No, that's another - unfortunately, that's another one of the myths, right. It would be great, we could all get zipped up on oxygen and feel better for it, but it turns out that no matter how fast or slow you breathe, you get generally the same amount of oxygen into your body and into your brain. What changes - and this turns out to be a powerful, powerful thing, and it makes yoga work in remarkable ways, is that you change your carbon dioxide metabolism.

You either hold more carbon dioxide in if you're breathing slowly or blow more off if you're breathing really fast. That has enormous physiological repercussions. It can help slow your body down, raise it up, do all kinds of neat stuff. It's a very powerful lever.

DANKOSKY: We're talking with William Broad about his book "The Science of Yoga: The Risks and the Rewards," taking your phone calls at 1-800-989-8255, 989-TALK. Let's go to Leslie(ph), who's calling from West Bloomfield, Michigan. Hi there, Leslie.

LESLIE: How are you doing?

DANKOSKY: Good, what's up?

LESLIE: I want to say, first off, I do yoga, my 10-year-old daughter does yoga in school. When she started - she goes to a private school, they do yoga there. They've noticed the kids are a lot more able to learn better. They take it in a whole lot easier, number one. And number two, I started yoga when I was diagnosed with high blood pressure, and I'm still on my meds, but I've gotten my blood pressure down to where my doctor is very happy.

BROAD: The book goes into a metastudy that was done, you know, 70, they looked at 70 different studies. There's no question that there's wonderful benefits for the heart because that relaxation, the lowering of your blood pressure, reducing hypertension, all those things are wonderful for cardiovascular health, just like Leslie's describing.

DANKOSKY: Now, a lot of the attention that's been paid to your book has to do with the injurious aspects of yoga. I know that you had - have had a couple of injuries. Maybe you can give me your story first, and we can try to go through this part of how dangerous yoga might be for some people.

BROAD: Can be, right. So right at the beginning of my research, in 2007, I am taking a very advanced class in Pennsylvania with a guy who I consider the Einstein of scientific yoga. We're all in there practicing, and we were paired off, right. And I'm paired with this rather attractive-looking woman, right, and I'm doing - she does her pose, and then I do the pose.

And she's kind of there to critique it and help me. And I'm kind of feeling my stuff, you know, like I'm - you know, I'm a lot older than they are, but hey, I'm doing great. And I was sort of strutting it, right. And then, all of a sudden, my lower back gives way.

And it's an explosion of fire, and my knees give way, and I'm crying. I can't see the room. I collapse and slam into a wall. And it was hugely embarrassing in addition to the pain, right. They all rush over: Oh, you poor guy, what's wrong? You know, and there I am in a, you know, pile on the floor kind of whimpering.

I had a pre-existing weakness in my lower back. So that was, you know, something I - you know, I was doing all kinds of stuff wrong. I shouldn't have been doing that. I shouldn't have been chatting with my partner. I should've been paying closer attention. That was a stupid, self-induced injury.

DANKOSKY: So - but when people read that chapter in your book, they will say, well, should I be more careful with what I'm doing? Is the problem that people are doing things that they can't physically do, or have new moves been introduced into yoga practice that people shouldn't even try?

BROAD: It's all kinds of stuff. It's a very complex picture. One of the big problems is that there are many, many, many inexperienced teachers out there, people who don't know about the range of human flexibility, the differences, you know, in human anatomy. They don't have the training to be able to spot, you know, problems on the horizon, big classes, lot of activity, lot of competitive pressure. That doesn't - Bikram yoga studios with mirrors, you know, you're not paying attention, oftentimes to your inner self and the warning signs, right?

You're kind of looking at the people next to you and looking at the mirrors and judging how you're doing compared to everybody else. But what I found in my research and what I try to lay out very carefully in the book is that there are some poses, right, that no matter how experienced the teacher is and how good you are, carry some significant risks of serious injury.

DANKOSKY: So which poses?

BROAD: The - literally, the killers are shoulder stand, headstand and plough position, things that put a lot of pressure or a lot of torque on your neck.

DANKOSKY: Anything that puts torque on the neck.

BROAD: Huge, you know, shoulder stand, you're doing about a 90-degree bend, right, between your body and your neck, and the mechanism is insidious. There are not well-known arteries that go up through the sides of your vertebrae into your brain. You torque those things around, and you can tear the inner linings. You do that, you start to get clots there. You come out of the pose, the clot sail into your brain, and you have a stroke.

DANKOSKY: But how often does this really happen? Because there are sports injuries in every single type of sport, in every activity...

BROAD: Sure.

DANKOSKY: ...how often does this sort of thing actually happen to people?

BROAD: No one knows. The federal government doesn't spend a lot of money on yoga. It spends no money on yoga epidemiology. The drug companies don't, right? But what you see are - and what I lay out in the book, over and over, are these case studies, right? One clinical report after another: yoga practitioner stroke, yoga practitioner stroke - over and over. And in response to the excerpt of the book in The New York Times article - The New York Times Magazine - the number of letters I got of injuries, including strokes, they don't show up in the medical literature so much anymore because it's a known threat.

Doctors, orthopedic surgeons, all these people know that extreme bending of the neck in yoga can be a risk factor for stroke, right? But they don't write about it anymore. It's known in the medical world, but not in the yoga world.

DANKOSKY: You would think somebody will be looking at this, but nobody is because?

BROAD: My own theory?

DANKOSKY: Sure.

BROAD: The yoga industrial complex has an economic incentive, right, to look the other way. Ask Philip Morris: Do cigarettes cause cancer? Absolutely not. Cigarettes are wonderful for you. Ask the complex: Does yoga cause injuries? Yoga is safe and wonderful. They just - if they know, they ignore it, right? Many of these people are uninformed. They don't know about the serious risks. And I hope they look at the book, so that they can get the details.

DANKOSKY: The book is "The Science of Yoga" by William Broad. I'm John Dankosky, and this is SCIENCE FRIDAY from NPR. We've got a call here from Sarah in Fulshear, Texas. Sarah, go ahead. You're on SCIENCE FRIDAY. Hi there. Sarah, are you there?

SARAH: Yes. Hi. Yes, I am. Hi.

DANKOSKY: Hi. What's your question?

SARAH: Can you hear me?

DANKOSKY: I sure can.

SARAH: Well, you know, I've been practicing hot yoga, Bikram yoga for three weeks now, and I'm in love. I absolutely love it. It is hard because it's practiced in a hot room.

DANKOSKY: Right.

SARAH: I don't know if your guest is also going to talk about that.

BROAD: I could.

SARAH: But I felt all the benefits from it - many benefits.

BROAD: Sure. It's good stuff. It makes you feel wonderfully flexible, and you can do great stuff in a hot studio.

DANKOSKY: So this is one type - many types of yoga...

BROAD: Right.

DANKOSKY: ...you talk about this yoga industrial complex, though...

BROAD: Yeah. Let's talk about...

DANKOSKY: Please continue.

BROAD: ...Bikram for one second?

DANKOSKY: Yeah, yeah.

BROAD: Because here's the downside, Sarah...

DANKOSKY: OK.

BROAD: ...that medical people worry about, that sense of elation that you get because you can push yourself farther and have all that good feedback and, you know, stir your hormones and do all that stuff, they worry about the loosening of your joints and your cartilage and your ligaments and all that stuff to - it makes joints unstable. Then you run a risk of dislocations, sprains, that kind of stuff. So the downside of Bikram is that you can get too loose, right? You can carry on this new flexibility in your joints and make yourself more injury prone. So be careful.

DANKOSKY: In your book, you actually - you write about people who hold positions for a very long time and get up and can't walk.

BROAD: Right.

DANKOSKY: And these are not extreme positions like the one you're talking about with your neck but just extreme...

BROAD: Held...

DANKOSKY: ...practice almost.

BROAD: ...held for a long time, yes.

DANKOSKY: Yeah.

BROAD: But the more mundane kind of injury is, you know, every complex joint, right? There's been a beautiful survey done out at - by a guy at Columbia University that looked in, you know, talked to yoga practitioners and therapists around the world, and you see this ranking. And it's like every complex joint, your shoulder, your knee, your lower back, all these places, right, are the things that in yoga are really, really prone to injury.

DANKOSKY: Of the other clear benefits that you write about, a boost in sex drive?

BROAD: Absolutely. That was one of the big surprises, right? I figured that was going to be a myth. And the science was kind of muddy. It took a lot of digging to clear it up. But when you get into it, you see hormones get zipped up. You see brainwaves, you know, being identical to those of lovers. And now, they've even done clinical studies in India where you have more than 100 men and women, right, who self-report before they do yoga what are their sex lives like after they do yoga. And across the board, it's like increased arousal, better orgasm, more overall satisfaction. They just basically give it rave reviews.

DANKOSKY: But, of course, this is the place - another thing you write this is where yoga all comes from. We all thought it was - I thought it was a spiritual thing. It comes from...

BROAD: Well, who knows?

DANKOSKY: Yeah.

BROAD: Maybe there's a spiritual aspect to sexuality, right? But it started out as this sex cult - tantra - right, back in medieval India. And hatha yoga, which we all practice, is a branch of tantric yoga, right? It was done to try to speed the tantric agenda, reach enlightenment faster. And it turns out a lot of those old tantric poses are very sexually arousing.

DANKOSKY: We're going to come back and take some more questions for William Broad, who's here from The New York Times, and his new book is "The Science of Yoga: The Risks and Rewards." The number is 1-800-989-8255. That's 1-800-989-8255 or 989-TALK.

This is SCIENCE FRIDAY. I'm John Dankosky in for Ira Flatow. We're talking with William Broad, whose new book is "The Science of Yoga: The Risks and Rewards." We want to get to Jennifer who's calling from Southern Pines, North Carolina. Hi there, Jennifer. You're on the air.

JENNIFER: Hi. I have a comment. I came in about 20 minutes ago and heard what he was saying about metabolism, and I feel like it's somewhat biased or inaccurate statement to say that it slows down your metabolism to the point where you would gain weight, and that yogis who don't are just, you know, using psychological tricks. I think it would be more accurate to say that yoga regulates your metabolism, and it does help you to slow down, but in a way that happens in the parasympathetic nervous system and helps you to reduce cortisol storage in other things that might...

BROAD: Right, right, right.

JENNIFER: ...cause you to gain weight.

BROAD: But right - but...

JENNIFER: And I'll take my response off the air. Thank you.

DANKOSKY: Thank you, Jennifer.

BROAD: You're right. It does all kinds of stuff. It can speed you up. It can slow you down. But in general, the effect of this new inner flexibility that you get is to relax you, right? And that's been measured over and over and over in lots of different studies. So the generality, you're right. You can get, you know, these sympathetic increases, and you do get speedups. But it's like you build up your body, right? You can lapse into new states of relaxation. Well, it's the same thing on the inside. You become more relaxed, and your metabolism tends to go down.

DANKOSKY: You mentioned this earlier. Talk more about mood and how it can help people with depression.

BROAD: Oh, yeah, yeah, yeah. I mean, that's one of the beautiful upsides of yoga, and it's the cutting-edge science, right? And everybody - most everybody knows that yoga relaxes you, makes you feel good in some fundamental way, right? But the research is clarifying that effect, right? Beautiful studies done at Harvard and Boston University is showing that yogis produce a wealth of important neurotransmitters - they're called GABA - and they are essential to mood control and regulation.

And it zips them up. It - and it makes them feel better. GABA is a strong anti-depressant. The issue is so important, right, a million people on this planet commit suicide every year because they can't envision, you know, getting to the next day. They can't see that light, that optimistic light out there. Just think, for free, by doing yoga, you stand a good chance of lifting your mood and being able to, you know, cut through those clouds of despondency.

DANKOSKY: Just very quickly - we heard from Jennifer. I knew that you're hearing a lot from people - yoga teachers, yoga practitioners around the country - not everyone is happy with this book because I think some people say but that's not the yoga I know. It does this for me, and that's not in your book. What sort of response are you getting to this?

BROAD: Well, I think a lot of those people haven't read the book, right? Because the book goes through so many benefits, right? Ones we haven't talked about - creativity, all kinds of, you know, counteracting aging, doing all that kind of stuff. Everybody tends to have a good experience, even people who injure themselves sometimes, like myself, right, keep going. But there's also - I think, there's commercial bias. A lot of the roar that I'm hearing and some of the letters, the invective, I mean I get a lot of mail, and I've gotten things like go F yourself, right, from, you know, a 30-year yoga teacher. I mean, very unyoga-like language, right...

(SOUNDBITE OF LAUGHTER)

BROAD: ...to say the least. They're - to me, that's the complex, right? They don't want to hear anything about any downside of yoga.

DANKOSKY: I didn't know about the yoga industrial complex until your book, but now, I do. William Broad is the author of "The Science of Yoga: The Risks and the Rewards." Thank you so much for joining us.

BROAD: It was a pleasure. Thank you.

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