Free The Science of Yoga by William J Broad

practitioners about the reports and investigations. This is pure speculation. But I’d be surprised if the community knows a hundredth or even a thousandth of what scientists have learned over a century and a half.
    This book tells that story. In essence, it offers an impartial evaluation of an important social phenomenon that began to stir millennia ago. And if I may, it is the first to do so.
    I have structured this book to start with issues of common interest and to end with topics that are less familiar. That flow, it turns out, parallels the development of scientific interest over the decades. So the book has a loose chronological organization.
    The portrait of yoga that emerges is quite different in important respects from the usual claims. In some cases, the news is better.
    For instance, a number of teachers credit yoga with powers of sexual renewal. The science not only confirms that claim but shows how specific poses can act as aphrodisiacs that produce surges of sex hormones and brain waves indistinguishable from those of lovers. More generally, recent clinical studies give substance to the idea that yoga can improve the sex lives of men and women, documenting how new practitioners report not only enhanced feelings of pleasure and satisfaction but emotional closeness with partners.
    The health benefits also turn out to be considerable. While many gurus and how-to books praise yoga as a path to ultimate well-being, their descriptions are typically vague. Science nails the issue.
    For example, recent studies indicate that yoga releases natural substances in the brain that act as strong antidepressants, suggesting great promise for the enhancement of personal health. Globally, depression cripples more than one hundred million people. Every year, its hopelessness results in nearly a million suicides.
    Amy Weintraub, a major figure in this book, recounts how yoga saved her life by cutting through clouds of despondency.
    But if some findings uplift, others contradict the onslaught of bold claims and proffered cures.
    Take body weight—a topic of enormous sensitivity for anyone trying to look good. For decades, teachers of yoga have hailed the discipline as a great way to shed pounds. But it turns out that yoga works so well at reducing the body’s metabolic rate that—all things being equal—people who take up the practice will burn fewer calories, prompting them to gain weight and deposit new layers of fat. And for better or worse, scientists have found that the individuals most skilled at lowering their metabolisms are women. Of course, other aspects of yoga do fight pounds successfully. The discipline builds body awareness and its calming influence can help reduce stress eating. Most yoga teachers are lithe, not lumpy. But when yoga succeeds at weight control, the scientific evidence suggests that it does so in spite of—not because of—its basic impact on the human metabolism.
    That’s one of yoga’s dirty little secrets. It turns out there are plenty of others, some quite significant.
    Yoga has produced waves of injuries. Take strokes, which arise when clogged vessels divert blood from the brain. Doctors have found that certain poses can result in brain damage that turns practitioners into cripples with drooping eyelids and unresponsive limbs.
    Darker still, some authorities warn of madness. As Carl Jung put it, advanced yoga can “let loose a flood of sufferings of which no sane person ever dreamed.” Many yoga books cite Jung approvingly but always seem to miss that quote. Even so, it represented his considered opinion after two decades of study and reflection.
    Overall, the risks and benefits turned out to be far greater than anything I ever imagined. Yoga can kill and maim—or save your life and make you feel like a god. That’s quite a range. In comparison, it makes most other sports and exercises seem like child’s play.
    My research has prompted me to change my own routine. I have deemphasized or