Sedentary lifestyle and not caloric intake may be to blame for increased obesity in the US, according to an analysis of data from the National Health and Nutrition Examination Survey (NHANES). A study, published in The American Journal of Medicine, has reported that in the past 20 years there has been a sharp decrease in physical exercise and an increase in average BMI while caloric intake has remained steady.
The researchers commented that a reduction in leisure-time physical activity, especially among young women, may be responsible for the upward trend in obesity rates.
“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 investigator, Dr Uri Ladabaum, Associate Professor of Medicine (Gastroenterology and Hepatology), Stanford University School of Medicine. “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.”
By analyzing NHANES data from the last 20 years, researchers from Stanford University discovered that the number of US adult women who reported no physical activity jumped from 19.1% in 1994 to 51.7% in 2010. For men, the number increased from 11.4% in 1994 to 43.5% in 2010. During the period, average BMI has increased across the board, with the most dramatic rise found among young women ages 18-39.
The study examined the escalation of obesity in terms of both exercise and caloric intake. While investigators did not examine what types of foods were consumed, they did observe that total daily calorie, fat, carbohydrate, and protein consumption have not changed significantly over the last 20 years, yet the obesity rate among Americans is continuing to rise.
Researchers also tracked the rise in abdominal obesity, which is an independent indicator of mortality even among people with normal BMIs. Abdominal obesity is defined by waist circumference of 88cm (34.65 in) or greater for women and 102cm (40.16 in) or greater for men.
Data showed that average waist circumference increased by 0.37% per year for women and 0.27% per year for men. Just like the rise in average BMIs, the group most affected by increased rates of abdominal obesity was women.
The proportion of adults who reported no leisure-time physical activity increased from 19.1% to 51.7% in women, and from 11.4% to 43.5 in men. The associated changes in adjusted BMIs were 8.3% higher among women and 1.7% higher among men with no leisure-time physical activity, compared to those with an ideal level of leisure-time physical activity.
“The prevalence of abdominal obesity has increased among normal-weight women and overweight women and men,” said 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.”
When Ladabaum et al grouped respondents to the most recent NHANES survey by race/ethnicity and age, they found that more than 50% of the workforce-aged adults in eight demographic subgroups reported no leisure-time physical activity.
Figure 1 shows the results and highlights the differences between the 1994 survey results and those collected in 2010 (albeit, with slightly different survey methods). According to this data, women, and black and Mexican-American women in particular, showed the greatest decreases in reported exercise.
Figure 1: Differences between the 1994 survey results and those collected in 2010.
While increased caloric intake is often blamed for rising rates of obesity, no association between these was found in this study; in contrast, an association was found between the trends over time for lack of physical activity and high BMI numbers.
“Our findings do not support the popular notion that the increase of obesity in the US can be attributed primarily to sustained increase over time in the average daily caloric intake of Americans,” concluded Ladabaum. “Although the overall trends in obesity in the US 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.”
This information was originally published by bariatricnews.net