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Lack of exercise not calories responsible for obesity epidemic

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According to a new study published on July 7 in the American Journal of Medicine, lack of exercise rather than excess calories is fueling the obesity epidemic in the United States. For the study, Stanford University researchers analyzed data from the National Health and Nutrition Examination Survey (NHANES). The study authors note that over the past two decades there has been a significant decrease in physical exercise and an increase in average body mass index (BMI); however, during that period, caloric intake has remained steady. They theorized that a nationwide drop in leisure time physical activity, particularly among young women, is responsible for the epidemic.

The investigators found that the number of adult women in the US who reported no physical activity soared from 19.1 % in 1994 to 51.7% in 2010. The largest increase was found among young women aged 18-39.The male gender was not far behind; the number of sedentary men rose from 11.4% in 1994 to 43.5% in 2010. The study found that, although significant increases in the proportion of adults reporting no leisure-time physical activity, there was no evidence of any changes of the average daily caloric intake.

The researchers evaluated the rise of obesity in terms of both exercise and caloric intake. They did not examine what types of foods were consumed; however, they did observe that total daily calorie, fat, carbohydrate, and protein consumption have not changed significantly over the last two decades. The investigators also traced the rise in abdominal obesity, which is an independent gauge of mortality even among individuals with a normal BMI. (Abdominal obesity is defined by waist circumference of 88 centimeters (34.65 inches) or greater for women and 102 centimeters (40.16 inches) or greater for men.) The study found that average waist circumference increased by 0.37% per year for women and 0.27% per year for men. Similar to the increase in average BMI, the group most affected by increased rates of abdominal obesity was women.

The investigators also categorized the survey subjects by race/ethnicity. Dramatic increases in obesity occurred among all ethnicities. The study found that more than 50% of the working-aged adults in eight demographic subgroups reported no leisure-time physical activity.

Take home message:

Although this study focuses the rise in obesity on lack of exercise, a healthy diet is also beneficial. It is prudent to both exercise and consume a healthy diet.