Mehmet Oz says that he yearns for the days “when our ancestors lived in small villages and there was always a healer in that village.” Photograph by Ethan Levitas

One evening a few weeks ago, several members of a television film crew crammed themselves into a tiny examination room on the seventh floor of the Research Medical Center, in Kansas City. The sun had set and the light was fading. Two men, one hoisting a big camera and the other a sound boom, stood in a corner less than a foot from one another. The hospital’s chief of medicine, the head of its cardiology department, and a nurse were also in the room. All were watching as a heavyset forty-six-year-old woman, with cornflower-blue eyes, a sweet smile, and auburn hair parted neatly in the middle, struggled to keep pace on a treadmill. Earlier that day, she had complained of chest pains, and had reported a family history of heart disease. Now she was taking a cardiac stress test, and it wasn’t going well. After little more than a minute, her blood pressure spiked, at 184/92. There was a third doctor there as well: Mehmet Oz, the heart surgeon and host of “The Dr. Oz Show,” which is among the most highly rated daily television programs in the nation. He stood a few inches away, obviously worried but urging her on. “In five seconds, this treadmill is going higher,” Oz said, in the soothing voice that has become recognizable to millions of viewers. The crew was filming a future episode, and Oz stared into the camera as he spoke: “I have to say this is where the battle will be won or lost.” One of the other doctors, sensing that the test might not last much longer, said to Oz, “If you want to do that pre-commercial thing, you’d better do it now.” Oz nodded and said, “I am very concerned. Your blood pressure is sky-high already. Your heart rate is racing to the moon.”

He asked the woman if she could last thirty more seconds. It wasn’t easy, but she did. As the woman gasped for breath, he continued, “I’ve got to say that I am disappointed in how deconditioned you are.” With her blood pressure showing no signs of easing, the physicians stopped the test. The woman stepped off the treadmill, sat on the edge of an examination table, and began to cry. “What got you so emotional?” the producer asked, then pointed at Oz: “Tell him!” The rest of the medical team inched awkwardly to the side, so the camera could home in on Oz and his patient. “It just upsets me that I am so out of shape,” she said. “I want to hike. I want to run around the yard with my grandbabies. My grandmother is ninety, and she is in better shape than me. I miss the old me.”

Oz asked gently, “If we could find the old you, would that be saving your life?” The woman nodded, then began to describe her descent into obesity, but again the producer waved her off. The shot had failed, and they would need to repeat it. Oz started over: “If we could find the old you, would that be saving your life?” He assured her that he would help “chip away the part of you that you don’t want, and you will find that the old you, the real you, is hidden inside.” The woman, still dizzy with exhaustion, nodded gratefully. The producer said, “Cut,” and everyone filed out of the room. It was 8 P.M. and Oz had been on his feet for twelve hours. More than a thousand people had come to the hospital that morning for Oz’s “15 Minute Physical,” part of a nationwide tour during which Oz, aided by many volunteers, takes people’s blood pressure, weighs them, measures the size of their waists, then checks their cholesterol and glucose levels. Oz chose those tests because the results are available immediately, and the information is useful and easy to understand. High blood pressure can be addressed with medicine and, often, by altering dietary habits. The same is true for obesity and, in most cases, diabetes.

Oz has become used to crowds, to adulation, and to fame. That morning, when he arrived in darkness, hundreds of people, mostly women, already stood in line at the entrance to the hospital; many lacked insurance, a doctor, or medical support of any kind. There were screams of delight when he hopped out of the car. People had come for the free exam and for helpful advice, but also to see him. Oz is fifty-two and jauntily fit, with a perfectly tamed helmet of brown hair and lengthy sideburns. His scrubs, powder blue and cinched at the waist, fit so well they looked as if they had been run up for him on Savile Row. In promotional pictures, Oz, with a stethoscope draped like a scarf around his neck, looks eerily like Doug Ross, the character that George Clooney made famous on “E.R.” He worked the line like a gifted politician, hugging people as they flipped open their phones and tried to get a picture with him. Many had brought old copies of magazines to be signed: Time, Good Housekeeping, Prevention—all with Oz on the cover. “I worship you, Dr. Oz,” one woman told him. Another threw her arms around his neck. “I haven’t seen a doctor in eight years,” she said. “I’m scared. You are the only one I trust.”

Oz squeezed her shoulder and stared into her eyes. “I’ll see you inside,” he said. “We are going to get through this, and we will do it together.”

Oprah Winfrey first referred to Mehmet Oz as “America’s doctor” in 2004, during one of his earliest appearances on her television show. The label stuck. Oz was a rare find: so eloquent and telegenic that people are often surprised to learn that he is a highly credentialled member of the medical establishment. Oz graduated from Harvard University in 1982. Four years later, he received joint medical and M.B.A. degrees from the University of Pennsylvania. He then moved to Columbia and New York-Presbyterian Hospital, where, as a surgeon specializing in heart transplants, he has served as vice-chairman and professor in the department of surgery for more than twenty years. (He still performs operations there each Thursday.) Oz also directs Columbia’s Cardiovascular Institute and Integrative Medicine Program, which he established in 1994, and has published scores of articles on technical issues, such as how to preserve muscle tissue during mitral-valve replacements. He holds a patent on a solution that can preserve organs and one on an aortic valve that can be implanted without highly invasive open-heart surgery.

By 2009, after dozens of appearances on “Oprah,” Oz had become so popular that Winfrey offered him his own show, produced by her company, Harpo. “The Dr. Oz Show” has since won two Emmys and averages nearly four million daily viewers. Certainly, no American physician has greater influence over a larger number of people. Oz has been named one of Esquire’s 75 Most Influential People of the 21st Century, as “the most important and most accomplished celebrity doctor in history.” He ranks consistently in the top ten on the Forbes list of most influential celebrities, and has been included on a similar list of Harvard University alumni. In 2008, Oz received the Ellis Island Medal of Honor. And, along with Michael Roizen, who is the director of wellness at the Cleveland Clinic, Oz is one of the “You Docs,” having written, over the past decade, a series of books, including “YOU: The Owner’s Manual”; “YOU: The Smart Patient”; “YOU: On a Diet”; “YOU: Staying Young”; “YOU: Losing Weight”; “YOU: Having a Baby”; “YOU: Stress Less”; and “YOU: Being Beautiful.” There are well over a million “YOU” books in print.