Sedentary Lifestyle to Blame for Increasing Obesity Rates Among Americans--Not Calories

If you think staying slim is all about what you eat, think again.

A recent study conducted by researchers from Stanford University in California found that sedentary lifestyle and not caloric intake is primarily responsible for increased obesity rates in the United States.

A new analysis of data from the National Health and Nutrition Survey (NHANES) shows that in the past 20 years, there has been a sharp decline in physical exercise and an increase in the average body mass index (BMI). However, throughout this time, caloric intake has remained relatively the same.

Researchers analyzed NHANES data throughout the past 20 years,  and found that the number of U.S. adult women who reported sedentary lifestyles increased from about 20 percent in 1994 to around 50 percent in 2010. Throughout this period, body mass index (BMI) also increased among many, but particularly young women ages 18-39.

"These changes have occurred in the context of substantial increases in the proportion of adults reporting no leisure-time physical activity, but in the absence of any significant population-level changes in average daily caloric intake," said lead study author Uri Ladabaum, MD, MS, Associate Professor of Medicine (Gastroenterology and Hepatology), Stanford University School of Medicine, via a news release. "At the population level, we found a significant association between the level of leisure-time physical activity, but not daily caloric intake, and the increases in both BMI and waist circumference."

The study examined the escalation of obesity for exercise and caloric intake. As investigators did not examine what types of food were consumed, they did study the total calorie, carbohydrate, fat and protein intake of participants. Findings revealed that, overall, despite steady caloric intake, obesity rates among Americans rose and are continuing to rise.

More specifically, researchers found a rise in abdominal obesity, even for those with normal BMIs. Increased waist circumference went anywhere from 34.65 inches or greater for women and 40.16 inches or greater for me. This shows a 0.37 percent increase in women per year and a 0.27 percent increase in men per year.

"The prevalence of abdominal obesity has increased among normal-weight women and overweight women and men," added Dr. Ladabaum. "It remains controversial whether overweight alone increases mortality risk, but the trends in abdominal obesity among the overweight are concerning in light of the risks associated with increased waist circumference independent of BMI."

High abdominal fat levels can greatly increase the risk of certai health issues, including cardiovascular issues, type 2 diabetes and colorectal cancer.

Though increased caloric intake can easily contribute to risking obesity rates, this study found no significant association between the trends over time. Decreased rates of exercise seemed to be blame primarily for rising obesity rates. 

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

More information regarding the findings can be seen via the American Journal of Medicine.