Lack of activity destroys the good condition of every human being, while movement and methodical physical exercise save it and preserve it.

—Plato

One credible hypothesis about the source of the epidemic of overweight and obesity in the United States is the progressive decrease in physical activity expended in daily life—for work, transportation, and household chores. Some researchers contend that the average caloric intake of Americans has not substantially increased; instead by reducing daily physical activity, the caloric imbalance between calories consumed and expended has shifted to favor weight gain. While no data conclusively prove this hypothesis, evidence does support it.

Among the recent studies that support the premise that Americans' sedentary lifestyles have precipitated the obesity epidemic is research that examined the diets of an Amish community in Ontario, Canada. In "Physical Activity in an Old Order Amish Community" (Medicine & Science in Sports & Exercise, vol. 36, no. 1, January 2004), researchers described the "Amish paradox—" that despite a diet that is high in fat, calories, and refined sugar, the Amish community had a scant 4% obesity rate, compared to 31% in the general U.S. population. Exercise science researcher David Bassett and his colleagues chose this particular Amish population because it has rejected technological advances such as automobiles and electricity, and its physically demanding lifestyle is in many ways comparable to the way Americans lived 150 years ago. (Other Amish communities that have assumed occupations less physically active than farming have obesity rates that are similar to those found in the general U.S. population.) The researchers analyzed the daily routines of about 100 Amish people and found that men averaged about 18,000 steps per day and women about 14,000, compared to the recommended 10,000 steps per day that most Americans struggle to achieve. The Amish men performed about ten hours per week of vigorous exercise and women spent about three-and-a-half hours engaged in heavy lifting, shoveling, digging, shoeing horses, or tossing straw bales. Men devoted an additional forty-three hours per week and women an average of thirty-nine hours to such moderate physical activities as gardening, performing farm-related chores, or doing laundry.