Obesity due primarily to lack of activity rather than overeating
Today in Cardiology
February 2005

Evidence suggests that energy intake in the United States has not increased over the past 40 years, but obesity has increased dramatically.

The obesity epidemic in the United States is more likely due to decreased activity rather than increased food intake, and strategies to combat obesity should reflect that, according to an editorial published in Mayo Clinic Proceedings.

According to the editorial written by Steven N. Blair, PED, and Milton Z. Nichaman, MD, ScD, at the Cooper Institute in Dallas, obesity has "increased astonishingly around the world," with a rate of about 20 percent at the start of the 21st century.

"We believe that the evidence suggests that declines in physical activity are more likely than increases in energy intake as the explanation for the recent increase in obesity prevalence," Blair and Nichaman wrote.

Assessing energy intake

To assess levels of energy intake, Blair and Nichaman analyzed food disappearance balance sheets and individual dietary surveys.

Food disappearance balance sheets, monitored by the Department of Agriculture, are estimated from food inventories, domestic food production, food imports and exports, and food used for nonhuman consumption. The assumption is that food that has disappeared has been consumed, and the balance sheets suggest that food consumption has increased since its nadir in 1960.

Blair and Nichaman argue that the food balance-sheet method is limited by the inability to take into account differing physiological needs of different segments of the population and make an accurate account of waste. Therefore, the estimates from food disappearance sheets are probably overstated.

Blair and Nichaman said the dietary surveys have shown no aggregate increase in energy intake, while the average weight in each population group has increased. "The evidence suggests that energy intake in the United States has not increased during the past 40 years, a period during which the prevalence of obesity has increased dramatically," Blair and Nichaman wrote.

Energy expenditure

According to Blair and Nichaman, increased obesity is caused by decreased physical activity primarily due to increased mechanization on the job, labor-saving devices at home and changing personal practices.

For example, using a remote control to change the channels expends less than 1 kcal as opposed to 3 kcal expended while getting up and changing the channel. Shopping online for an hour expends 30 kcals, compared to expending 145 kcals to 250 kcals while shopping at the mall for an hour. Taking an elevator up three flights expends 0.3 kcal, compared to 15 kcal expended taking the stairs.

Blair and Nichaman outlined 20 activity areas where Americans have moved to more sedentary practices. They suggest that over the course of a month a person who chooses the sedentary route would expend 1,700 kcals compared to 10,500 kcals with the more active choices, for a difference of 8,800 kcals.

This is the energy equivalent of 2.5 pounds of body fat, which would equate to 30 pounds in a year.

"There are dozens of similar examples of many ordinary activities," Blair and Nichaman wrote. "Although only a few kilocalories can be related to any specific sedentary activity, compared with its active counterpart, the end result is a substantial weight change over time."

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