Not everyone sees this potential revolution as a good one. Do people really want or need to know this much about themselves? Is such a preoccupation with health even healthy? What if swimming in oceans of bio-data causes more harm than good?

“Frankly, I’d rather go river rafting,” says Dr. H. Gilbert Welch, a professor of medicine at the Dartmouth Institute for Health Policy and Clinical Practice, and the author of Overdiagnosed: Making People Sick in the Pursuit of Health. “Data is not information. Information is not knowledge. And knowledge is certainly not wisdom.” Welch believes that individuals who monitor themselves as closely as Larry does are pretty much guaranteed to find something “wrong.” Contradictory as it sounds, he says abnormality is normal.

“It brings to mind the fad a few years ago with getting full-body CT scans,” Welch says. “Something like 80 percent of those who did it found something abnormal about themselves. The essence of life is variability. Constant monitoring is a recipe for all of us to be judged ‘sick.’ Judging ourselves sick, we seek intervention.” And intervention, usually with drugs or surgery, he warns, is never risk-free. Humbler medical practitioners, aware of the sordid history of some medical practices (see: bloodletting, lobotomy, trepanning), weigh the consequences of intervention carefully. Doing no harm often demands doing nothing. The human body is, after all, remarkably sturdy and self-healing. As Welch sees it, “Arming ourselves with more data is guaranteed to unleash a lot of intervention” on people who are basically healthy.

Not to mention creating an epidemic of anxiety. In other words, the “quantified life” might itself belong to the catalog of affliction, filed under Looking too closely, hazards of.

In that sense, the story of Larry Smarr might be less a pioneering saga than a cautionary tale.

Larry’s journey started with that most American of preoccupations, losing weight. Larry doesn’t update the photo each time he renews his California driver’s license, preferring to keep, as a reminder, the one taken soon after his arrival at UCSD 12 years ago, with his wife, Janet. It shows a 51-year-old Larry, one with more and longer hair, a wide, round face, and an ample second chin. Call him Jolly Larry. He had just arrived from Illinois, a place he now refers to as “the epicenter of the obesity epidemic,” and he had a girth to match his oversize professional reputation. (Deep-fried, sugarcoated pastries were a particular favorite of his back then.) Arriving in La Jolla, Jolly Larry found himself surrounded by jogging, hiking, biking, surfing, organic-vegetable-eating superhumans. It was enough to shame him into action. If he was going to fit in on this sunny new campus, he would have to shape up.

So Jolly Larry started working out, reading diet books, and stepping on the scale every day. At first, his charts were disappointing. Like countless strivers before him, he dropped some weight, but not much, and it kept wanting to come back. Three or four popular books on weight loss left him mostly confused, but they did convey a central truth: losing weight was only 20 percent about exercise. The other 80 percent was about what he put in his mouth. What triggered his breakthrough was the advice of Barry Sears, the biochemist who created the Zone Diet, which pressed Larry’s buttons precisely. Sears proposed that to diet more effectively, one needed to know more. Larry decided to study up on his body chemistry.

Few people in history have been better positioned to act on such advice. Larry had begun his professional life as an astrophysicist, trying to unravel the core puzzles of the universe. In 1975, when he was working toward his doctorate at the University of Texas, one of his advisers suggested that he get a top-secret government security clearance: behind the walls of America’s nuclear-weapons program were not only some of the nation’s premier physicists, but also the world’s first supercomputers, hundreds of times faster than anything available on any college campus. Larry got his clearance, and in the following years, while working as a fellow at Princeton and at Harvard, he would disappear during summers behind the classified walls of the Lawrence Livermore National Laboratory, in the San Francisco Bay Area. There he would work 16-hour shifts on some of the most difficult problems in his field—but with a crucial difference. Working with a computer at one of his universities, Larry might set it a task to compute overnight. He would go home, and when he returned the next morning, the task would be nearing completion. Working with the new Cray supercomputer at Livermore, he could get the same result in a minute and a half.