DR. LEVINE’S MAGIC UNDERWEAR resembled bicycle shorts, black and skintight, but with sensors mounted on the thighs and wires running to a fanny pack. The look was part Euro tourist, part cyborg. Twice a second, 24 hours a day, the magic underwear’s accelerometers and inclinometers would assess every movement I made, however small, and whether I was lying, walking, standing or sitting.
James Levine, a researcher at the Mayo Clinic in Rochester, Minn., has an intense interest in how much people move — and how much they don’t. He is a leader of an emerging field that some call inactivity studies, which has challenged long-held beliefs about human health and obesity. To help me understand some of the key findings, he suggested that I become a mock research trial participant. First my body fat was measured inside a white, futuristic capsule called a Bod Pod. Next, one of Dr. Levine’s colleagues, Shelly McCrady-Spitzer, placed a hooded mask over my head to measure the content of my exhalations and gauge my body’s calorie-burning rate. After that, I donned the magic underwear, then went down the hall to the laboratory’s research kitchen for a breakfast whose calories were measured precisely.
A weakness of traditional activity and obesity research is that it relies on self-reporting — people’s flawed recollections of how much they ate or exercised. But the participants in a series of studies that Dr. Levine did beginning in 2005 were assessed and wired up the way I was; they consumed all of their food in the lab for two months and were told not to exercise. With nary a snack nor workout left to chance, Dr. Levine was able to plumb the mysteries of a closed metabolic universe in which every calorie, consumed as food or expended for energy, could be accounted for.
His initial question — which he first posed in a 1999 study — was simple: Why do some people who consume the same amount of food as others gain more weight? After assessing how much food each of his subjects needed to maintain their current weight, Dr. Levine then began to ply them with an extra 1,000 calories per day. Sure enough, some of his subjects packed on the pounds, while others gained little to no weight.
“We measured everything, thinking we were going to find some magic metabolic factor that would explain why some people didn’t gain weight,” explains Dr. Michael Jensen, a Mayo Clinic researcher who collaborated with Dr. Levine on the studies. But that wasn’t the case. Then six years later, with the help of the motion-tracking underwear, they discovered the answer. “The people who didn’t gain weight were unconsciously moving around more,” Dr. Jensen says. They hadn’t started exercising more — that was prohibited by the study. Their bodies simply responded naturally by making more little movements than they had before the overfeeding began, like taking the stairs, trotting down the hall to the office water cooler, bustling about with chores at home or simply fidgeting. On average, the subjects who gained weight sat two hours more per day than those who hadn’t.
People don’t need the experts to tell them that sitting around too much could give them a sore back or a spare tire. The conventional wisdom, though, is that if you watch your dietand get aerobic exercise at least a few times a week, you’ll effectively offset your sedentary time. A growing body of inactivity research, however, suggests that this advice makes scarcely more sense than the notion that you could counter a pack-a-day smoking habit by jogging. “Exercise is not a perfect antidote for sitting,” says Marc Hamilton, an inactivity researcher at the Pennington Biomedical Research Center.
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