CLEVELAND -- If Terry Prewitt's body were a house, not too long ago the interior would have been dirty and her pipes clogged, choked by the damage caused by a two-pack-a-day smoking habit.

In search of a do-it-yourself guide for making body repairs, Prewitt turned to a Cleveland Clinic physician, Michael Roizen, who prescribed a smoking cessation plan that included substituting 30 minutes of daily exercise for nicotine. Roizen, who at the time was chairman of the University of Chicago's department of Anesthesia and Critical Care in Prewitt's hometown, was relentless in encouraging his patient to stay away from the butts and to keep her butt moving. She's been smoke free since March 2004.

"I was completely resigned to being a smoker. I totally did not think that I would be successful in my campaign to stop smoking," says the 54-year-old Prewitt.

The plan that helped her quit is included in the hugely popular book "You: The Owner's Manual," written by Roizen and Mehmet Oz, a professor and vice chairman of surgery at Columbia University in New York.

With its thematic metaphor that the human body is a house -- the heart is the water main, the digestive system part of the plumbing and the bones are the foundation -- the book has sold 1.5 million copies in little more than six months. It has been on The New York Times list of best sellers for 28 weeks, currently No. 7 in nonfiction advice.

The easy-to-understand guide to healthy living is written with hip, simple language that makes the advice not only educational but, at times, laugh-out-loud fun, even with topics once resigned to uncomfortable conversations with doctors.

A section about how to tell if your intestines are working properly contains this passage: "Let's look down into the toilet and do a self-test (c'mon, you're alone anyway). Your feces should be S-shaped (the shape of your rectum as it nears your anus), as opposed to gumball-sized pellets. ... You can also do the sound test. The optimum feces enters the water like Greg Louganis -- no splash."

Roizen, 59, heads the Cleveland Clinic's anesthesiology, critical care and pain management division and has been a best seller before his "RealAge" series, which describes research and lifestyle choices intended to fight diseases that come with aging. The 45-year-old Oz is best known for his appearances on the Discovery Health Channel's "Second Opinion."

The pair worked closely with former magazine writer Ted Spiker, Oz's wife, Lisa Oz, and illustrator Gary Hallgren to get the edgy, humorous tone they wanted in "You: The Owner's Manual."

It's all part of what Roizen describes as a quest to change the nation's health.

"Getting people to understand it is the best feeling," he says in an interview at his spacious Cleveland office, where he reads through 150 thank-you e-mails a day, works on chapters for upcoming books and completes his clinic duties. A typical week for Roizen totals 80 hours.

Oz shares Roizen's passion. He speaks so quickly as he zips through the pair's to-do list (a "You" manual for children, a "waist management" plan book, a text for menopausal women, an easy guide for navigating the complex health-care system) that it's hard to keep up.

What's clear is his shared goal of getting Americans to take charge of their bodies.

"We are an incredibly well-educated society," he says. "But we are not a motivated society." Their book seeks to inspire change, he says. "What's lacking usually is not knowledge but understanding -- understanding what happens if you do it or don't do it is insight."

The book offers sobering incentives: axing unhealthy habits such as a fat-heavy diet and adding healthier choices such as daily exercise can add years to your life, the doctors write.

With each tidbit of what you should do, the authors offer the payoff in life years. For example, a smoker can gain a year of life after just two months of quitting. Five years of being cigarette-free can amount to seven more years, the book says.

"The reason why I am a fan is because the book works. I dedicated my life to it and in return it has saved my life. I was over 200 pounds and now I am 154 pounds," said 33-year-old Alexandra Weeks of Beebe, Ark.

For Oz and Roizen, the real life reviews have been the best kind. Their biggest goal is that the book will help patients and physicians focus on the positive results of a healthy lifestyle instead of the negative outcomes of the alternative.

"We believe in educating patients," Roizen said. "We've got something that's going to change the health of the nation."