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Without exercise, Americans are growing more obese, according to Stanford researchers

gym_smallerMore than half of all American women don't exercise at all, according to a survey that tracked the health of nearly 7,000 people in 2009 and 2010. Men don't fare much better: 43 percent don't work out at all.

Those percentages are dramatically higher than results from a similar study conducted in the early 1990s, which uncovered only 19 percent of sedentary women and 11 percent of inactive men.

More troubling, obesity rates jumped during the same period, according to an analysis by Stanford researchers published in the August issue of The American Journal of Medicine and now available online in a draft form.

What gives? Experts have been intoning "exercise 30 minutes a day most days" for more than a decade. People are just lazy, right?

It's not that simple, says Pamela Powers Hannley, MPH, the journal's editor, in a sharply worded commentary that accompanies the study. Many women work long hours, then spend their "spare" time parenting, not jogging, Hannley said. Exercise alternatives need to be convenient and low-cost, Hannley said, noting that some communities, like Tucson, Arizona, where she lives, are considering reducing hours at swimming pools or even closing pools entirely to save money.

"It's going to take widespread change, not just individual change, not just an app for your iPhone," Hannley says.

She, along with primary study author Uri Ladabaum, MD, associate professor of gastroenterology, heartily endorse the five recommendations issued by the Institute of Medicine in 2012. They are: integrate physical activity into daily life; make healthy food choices easy and routine; reinvigorate messages about exercise and food; focus on schools; and expand the role of employers, medical professionals and insurers.

Some people, including my editor here at Stanford, aren't convinced that exercise can single-handedly curb obesity. Diet, the other obvious causal factor, didn't play a leading role in this data set. The study considered the total calories consumed, but that didn't vary significantly from 1988 to 2010, Ladabaum and his colleagues write. Genetics, environment and plain 'ol chance all play a role in overall weight.

This study dug up another worrying trend, as well, one that particularly jumped out to second author, Ajitha Mannalithara, PhD, a Stanford social science research associate: Independent of weight, Americans are getting thicker around the middle.  The incidence of so-called abdominal obesity climbed from 46 percent to 62 percent in women and from 29 to 42 percent in men.

Abdominal girth is linked to increased risks of cancer and cardiovascular disease, even in normal weight individuals, Mannalithara said.

The stats are all based on the robust National Health and Nutrition Examination Survey, a long-term project of the Centers for Disease Control and Prevention that collects information from both surveys and physical examinations to assess Americans' health.

Becky Bach is a former park ranger who now spends her time writing, exploring, or practicing yoga. She's currently a science writing intern in the medical school's Office of Communication & Public Affairs.

Previously: Lack of exercise shown to have largest impact on heart disease risk for women over 30, More evidence that boosting Americans' physical activity alone won't solve the obesity epidemic, To meet weight loss goals, start exercise and healthy eating programs at the same time and Study shows regular physical activity, even modest amounts, can add years to your life
Photo by Ms. Phoenix

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