Inactivity may explain obesity epidemic

Lack of exercise – and not a tendency to eat too much – may explain why an increasing number of Americans are obese, a new study suggests.

Researchers analysed US government data from the last 20 years and found that the number of women who reported no physical activity rose from about 19 percent in 1994 to nearly 52 percent in 2010. The number of men who said they didn't exercise increased from about 11 percent to about 43 percent.

Black and Mexican-American women showed the greatest decreases in reported exercise, the study authors found.

During the study period, there was an increase in adults' average body mass index (BMI), an estimate of body fat based on height and weight, with the most dramatic rise among women aged 18 to 39. The researchers also found increased rates of abdominal obesity, especially among women.

Read: Body Mass Index (BMI)

Obesity epidemic

At the same time, calorie intake among adults remained steady during the study period, according to the findings reported recently in the American Journal of Medicine.

While the investigators found an association between inactivity and the obesity epidemic, the study did not prove a cause-and-effect relationship.

"Our findings do not support the popular notion that the increase of obesity in the United States can be attributed primarily to sustained increase over time in the average daily caloric intake of Americans," lead investigator Dr. Uri Ladabaum, an associate professor of medicine at Stanford University School of Medicine, said in a journal news release.

"Although the overall trends in obesity in the United States are well appreciated and obesity prevalence may be stabilising, our analyses highlight troublesome trends in younger adults, in women, and in abdominal obesity prevalence, as well as persistent racial/ethnic disparities," Ladabaum added.

Read: Belly fat adds to diabetes risk

Pamela Powers Hannley, journal managing editor, wrote in an accompanying commentary: "If we as a country truly want to take control of our health and our health care costs, [this study] should be our clarion call. From encouraging communities to provide safe places for physical activity to ensuring ample supply of healthy food to empowering Americans to take control of their health, we must launch a concerted comprehensive effort to control obesity."

More information

The US National Institute of Diabetes and Digestive and Kidney Diseases offers tips to help you get active.

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(Image: Fat man is laying on the couch topless watching the TV. Guy is overweight and quite lazy looking from Shutterstock.