Rise in Obesity More About Inactivity Than Caloric Intake

t's no news that Americans have become more obese during the past 15 years, but a new study adds an interesting perspective—the dramatic gains may be almost entirely due to lack of physical activity, and not an increase in caloric intake.
In an article e-published ahead of print in the American Journal of Medicine (abstract only available for free), researchers examined data from National Health and Nutrition Examination Surveys (NHANES) administered between 1988 and 2010. Much of what they discovered about rates of obesity, overweight, and abdominal obesity have been well-substantiated, but some twists to the story were uncovered when researchers looked at these data in terms of caloric intake and levels of physical activity.
What they found was that in comparing the 2 surveys, caloric intake "did not change significantly over time for women or men as a whole, or when stratified by race/ethnicity." On the other hand, they write, the number of Americans who reported engaging in no leisure-time physical activity tripled on average, from 15.3% to 47.6%. Authors believe the results lend more support to the Institute of Medicine's efforts to link physical activity to obesity reduction.
Comparing the sexes, 51.7% of women reported engaging in no leisure-time physical activity, compared with 19.1% 15 years prior. Inactivity rates for men rose as dramatically, though not as high, from 11.4% to 43.5%.
During the same period, rates of obesity, overweight, and abdominal obesity (defined as waist circumference of 34 inches or more in women, and 40 inches or more in men) climbed, with women reporting more significant increases than men. Obesity prevalence in women increased from 24.9% to 35.4%, and rose from 19.9% to 34.6% in men.
"Average BMI, average waist circumference, the prevalence of abdominal obesity increased substantially over the past 2 decades in both women and men," authors write. "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 caloric intake."
Among other findings in the study:
Over the past 2 decades, the average BMI in the US increased by .37% every year in both men and women.
Average waist circumference increased for all groups, but for women was largest among non-Hispanic blacks. Non-Hispanic whites were the male group with the largest rate of increase.
Among adults categorized as normal weight based on BMI, the rate of abdominal obesity increased significantly in women, from 9.6% to 13.8%.
Among women and men, rates of inactivity were higher among non-Hispanic blacks and Mexican-Americans.
APTA strongly supports the promotion of physical activity and the value of physical fitness to prevent obesity, and has representatives on the board of the National Physical Activity Plan Alliance. The association offers several resources on obesity, including continuing education on childhood obesity, and a prevention and wellness webpage that links to podcasts on the harmful effects of inactivity.
Research-related stories featured in PT in Motion News are intended to highlight a topic of interest only and do not constitute an endorsement by APTA. For synthesized research and evidence-based practice information, visit the association's PTNow website.