Stand Up Before You Hurt Yourself!

A few months ago, Travis Saunders wrote at the Scientific American Guest Blog about the dangers of excessive sitting. He warned that those of us who faithfully log our exercise hours might still be at an increased risk of negative health effects if we spend too many hours sitting at a desk or lounging on the couch. This isn't just because sitting burns fewer calories than walking or standing, but because sedentary behavior is associated with changes in triglyceride uptake, HDL cholesterol, and insulin resistance. (Go read the whole thing.)

Now, the New York Times Magazine is taking on the issue with its provocatively titled "Is Sitting a Lethal Activity?" piece (nearly as alarming as the companion piece "Is Sugar Toxic?"). James Vlahos describes the research of Mayo Clinic researcher James Levine, who's been studying activity and obesity using "magic underwear" that precisely tracks wearers' movements twice per second for days at a time. Here's one of his findings, described by Vlahos:

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.

... The good news is that inactivity's peril can be countered. Working late one night at 3 a.m., Dr. Levine coined a name for the concept of reaping major benefits through thousands of minor movements each day: NEAT, which stands for Non-Exercise Activity Thermogenesis. In the world of NEAT, even the littlest stuff matters. McCrady-Spitzer showed me a chart that tracked my calorie-burning rate with zigzagging lines, like those of a seismograph. "What's that?" I asked, pointing to one of the spikes, which indicated that the rate had shot up. "That's when you bent over to tie your shoes," she said. "It took your body more energy than just sitting still."

Through a quick PubMed search, I found a free 2008 article in the journal Diabetes that describes another study by Levine and colleagues using a similar setup of carefully tracked movements and overfeeding. (After the study, "all subjects were assisted, as needed, to lose any excess weight that had been gained" -- but I'm guessing the Mayo institutional review board had some reservations approving overfeeding of human subjects.) The 22 subjects were found to walk a total of about seven miles per day (mostly through short, low-intensity walks), but the obese subjects logged one-third less distance than their lean counterparts. The finding that really surprised me, though, was that when subjects were overfed, their daily walking distance decreased. Here's the writeup:

If the mechanism(s) that underlies obesity is associated with a decline in walking distance, we wondered whether experimental weight gain would be associated with decreased walking. To examine this, we compared the walking characteristics of all of the volunteers after 8 weeks of overfeeding by 1,000 kcal/day above weight-maintenance needs. We thereby analyzed 10,438 bouts of walking after 56,000 kcal of overfeeding in a similar fashion to the weight-maintenance baseline. All of the subjects gained weight in a fashion compatible with lifelong weight gain; the average weight gain was 3.6 ± 1.6 kg, and the average fat gain was 2.8 ± 1.7 kg; P < 0.0001. With overfeeding, daily walking distance decreased by 1.5 miles/day (P = 0.0005) (Fig. 4B). The number of walking bouts and total daily walking time was constant with weight gain (Table 2; Fig. 4C). The decrease in walking distance with overfeeding occurred because the bouts of walking became significantly shortened through a decrease in free-living walking velocity (P = 0.0007; Table 2). The greater the decrease in the velocity with overfeeding, the greater the decrease in walking distance (Fig. 5; r = 0.81; P < 0.0001). The magnitudes of the decreases in walking associated with overfeeding were similar for the lean and obese subjects (Table 2).

Research by Levine and others demonstrates that the relationship between physical activity, obesity, and metabolic effects is not as straightforward as we might assume. This doesn't mean we should ignore traditional weight loss advice - "eat less, move more" is still a good guide for most of us - but it should prompt us to realize that our unconscious movements might affect our health efforts more than we've realized. In other articles, Levine and his co-authors suggest ways to integrate more movements into daily life. And if you're sitting down to read this, you might want to stand up and walk around a bit.