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Biology May Keep Couch Potatoes Supine

Genetic predisposition to sit can pack on pounds, study suggests

THURSDAY, Jan. 27, 2005 (HealthDayNews) -- Got a mind to recline? So do millions of obese Americans, according to a study that suggests some people may be biologically designed to remain seated.

In unusual research involving uniquely designed underwear, researchers found that obese people stand or move about much less during waking hours than lean people do, and therefore burn an average 350 fewer calories per day.

Even more intriguing, the study found this tendency to stay seated remained unchanged in the obese people even after they dieted down to a healthy weight.

"It's very clear from our study that this phenomenon is not due to a volitional lack of willpower -- in fact, it's quite the opposite. There seems to be, in some people, a biological drive to be seated," said lead researcher Dr. Jim Levine, a professor of medicine at the Mayo Clinic, in Rochester, Minn.

The findings are published in the Jan. 28 issue of Science.

Federal health officials recently labeled America's obesity epidemic a major killer, linked to more than 400,000 deaths per year. While increased food intake is credited with much of the blame, falling activity rates are helping widen waistlines, too.

Levine has been studying the physiological mechanisms that underlie activity -- and sloth -- for years. In this latest research, his team recruited 10 lean and 10 healthy, mildly obese adults-- those who had a BMI of 33 or above -- for a study of what scientists call "NEAT."

"NEAT stands for non-exercise activity thermogenesis -- the calories we burn in all our normal daily activities," Levine explained. "That's stuff like cleaning the house, walking to work, twiddling your thumbs -- anything except actual exercise."

For 10 days, the 20 volunteers ate specially prepared meals and wore a type of high-tech underwear embedded with tiny sensors that recorded body movements on a second-by-second basis.

"We found that obese people have remarkably different NEAT, compared to their lean counterparts," Levine said. In fact, undergarment readings confirmed that the obese participants sat or reclined an average 2.5 hours more per day than their skinny peers.

This reduction in movement meant that individuals in the overweight group burned up 350 fewer calories per day than those in the lean group, Levine said. That's significant: According to the researchers, a loss of 350 calories per day could lower weight by 33 pounds over the course of a year.

Of course, one explanation for the disparity between the two groups is that being heavy simply discourages the obese from moving around. To test that theory, Levine went back and again recorded the movement patterns of 16 of the original 20 participants.

But there was a catch: "We took the lean people and we had them overfeed and gain weight, to see if they'd end up sitting in their chairs," Levine said. "You'd think that if obesity was driving this tendency to sit, that these newly obese individuals would end up just sitting there. But they didn't -- they remained standing, and ambulatory."

Similar results were seen after the originally obese participants slimmed down. Despite their newly svelte status, these participants continued to prefer lounging over being more active. "This drive seems very fixed," he said.

The researchers speculate that obese individuals may respond differently to stimuli that encourage leaner folk to get moving. "Right now we just don't know the underlying mechanism, but it does seem to be biologically driven," Levine said. "It's remarkably consistent."

Dr. Frank Hu, a professor of nutrition and epidemiology at Harvard School of Pubic Health, called the findings "intriguing."

"This basically supports the idea that any activity is better than nothing," said Hu, whose own work has focused on the link between sedentary lifestyles and killer illnesses such as diabetes and heart disease.

"Obviously, for couch potatoes, the worst scenario is just to sit there without moving," Hu added. "Slightly better would be to watch TV and be moving around; and better still would be to put a treadmill in front of the TV, and use it."

Levine believes environments have to change to encourage everyone, especially those predisposed to inactivity, to get moving.

"We have to remember that biology hasn't changed in the past 50 years, but obesity rates have skyrocketed," he said. "So there's obviously some huge environmental change towards inactivity that's allowed people with this genetic predisposition to sit more."

According to Levine, "The question we now have to ask is, 'What can we do to make our environments more activity-friendly?' "

More information

Thinking about getting more active? Head to the American Council on Exercise.

SOURCES: Jim Levine, M.D., consultant endocrinologist and professor, medicine, Mayo Clinic, Rochester, Minn.; Frank HU, M.D., Ph.D., associate professor of nutrition and epidemiology, Harvard School of Public Health, Boston; Jan. 28, 2005, Science
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