In The Science of Yoga, William J. Broad brings something unusual to his subject: an open mind.

Broad, the book's biographical note informs us, has practiced yoga since 1970. For nearly that long he has also been a science reporter for The New York Times, writing books like Teller's War: The Top-Secret Story Behind the Star Wars Deception along the way.

Broad's objective is simple enough: to evaluate in scientific terms the claims made for yoga. But this turns out to be more complicated than it seems. For one thing, there are the sheer number and variety of those claims: Yoga, it is said, can prevent heart disease, reverse aging, eliminate pain and bestow serenity and peace.

Broad patiently and exhaustively examines the evidence for each of these assertions, revealing surprises along the way. Yes, yoga can reduce anxiety and improve mood. No, it won't help the overweight shed pounds. Yes, it may actually slow the body's biological clock.

Broad doesn't just discuss the results of the scientific literature; he weighs the relative prestige of the journal in which the studies were published and scrutinizes each experiment's design and methodology. This is more information than some readers may want, but Broad leaves no doubt that he's done his homework.