As our country's obesity problem has gained more attention in recent years, many have looked to identify the root of the problem. A recent 20-year study conducted by Stanford University revealed that obesity is not due primarily to over-eating but rather a decline in exercise, which leads to increases in average body mass index (BMI). Categories examined by lead author Uri Ladabaum and his colleagues include: obesity, waistline obesity, physical activity and calorie intake. 

"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," said Ladabaum, an associate professor of medicine at Stanford. "We found a significant association between the level of leisure-time physical activity, but not daily caloric intake, and the increases in BMI and waist circumference."

In 1994, only 19.1 percent of women admitted to not having any physical activity in their lifestyle, but by 2010, 51.7 percent for women reported that they did not work out. Men only produced 11.4 percent of those who didn't work out in 1994, but saw an increase in 2010 to 43.5 percent. BMI has increased 0.37 percent per year for women and 0.27 percent for men. The researchers found this was the case for both normal-weight and overweight women, while only for overweight men.

Racial groups hit hardest by lack of exercise are African-American and Mexican-American women, according to the study.