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Obesity is Leveling Off, but not Declining
According to new data released by the Centers for Disease Control and Prevention and published online January 17, 2012, in the Journal of the American Medical Association, obesity among American adults and children has leveled off in recent years.
The findings are based on the 2009 and 2010 height and body weight data of 6000 adults and 4000 children collected from the National Health and Nutrition Examination Survey, which has been conducted since 1960. The rates of obesity were compared with results from previous periods.
The prevalence of obesity was 35.7% for adult men and 35.8% for adult women. Compared with the period from 1999 to 2010, there was no significant increase in obesity rates for women overall; however, non-Hispanic black women and Mexican American women showed a small but statistically significant increase in obesity prevalence. Men showed a statistically significant increase in obesity compared with rates from 1999 to 2010. When compared with 2003 to 2008 data, there was no significant difference in either men or women.
Among children and adolescents aged 2 to 19 years, the prevalence of obesity was 16.9% for 2009 to 2010. Compared with 1999 to 2000, there was a significant increase in obesity for boys but not for girls. Neither boys nor girls showed a significant increase compared with 2007 to 2008 results.
These comparisons show a leveling off in obesity, but America still has a higher prevalence compared with other developed nations, such as Canada and England. Obesity levels are the highest they have ever been.
Biology Can Make Weight Loss Harder
In the article “The Fat Trap,” published in the December 28, 2011, issue of The New York Times Magazine, author Tara Parker-Pope discusses the biologic challenges of losing weight and successfully keeping it off. The article reviews research showing that the biggest challenge for obese patients to overcome is the body’s own mechanisms that try to gain back the previously lost weight.
Findings from an October 2011 study published in the New England Journal of Medicine show that obese subjects placed on a low-calorie diet for 8 weeks were in an altered hormonal state. Levels of the hunger-stimulating hormone ghrelin were increased and levels of the hungersuppressing hormones YY and leptin were reduced compared with pre-diet levels.
Other research has shown how variations in genetics can dramatically alter how much weight different people gain when caloric intake and activity levels are held constant. To date, 32 distinct genetic variations associated with obesity and body mass index have been identified. Biopsies of muscle fibers show that obese subjects who had lost weight require more work to burn the same number of calories as normal weight individuals at the same weight. Additionally, the brains of subjects after weight loss showed increased activity on magnetic resonance imaging scans in response to food compared with scans from before their weight loss. These findings suggest that the body induces a desire for food in individuals who have lost weight.
Knowing all of this may help dispel the notion that failure to lose weight is caused by laziness, poor will power, and overindulgence, and serve to help develop better weight loss strategies for obese individuals.
1. Flegal KM, Carroll MD, Kit BK, et al. Prevalence of obesity and trends in the distribution of body mass index among US adults, 1999-2010. JAMA. 2012;307(5). doi:10.1001/jama.2012.39.
2. Ogden CL, Carroll MD, Kit BK, et al. Prevalence of obesity and trends in body mass index among US children and adolescents, 1999-2010. JAMA. 2012;307(5). doi:10.1001/jama.2012.40.
3. Parker-Pope T. The fat trap. The New York Times Magazine. December 28, 2011. www.nytimes.com/2012/01/01/magazine/tara-parker-pope-fat-trap.html.
4. Faith MS, Van Horn L, Appel LJ, et al. AHA scientific statement: evaluating parents and adult caregivers as "agents of change" for treating obese children: evidence for parent behavior change strategies and research gaps: a scientific statement from the American Heart Association. Circulation. Published online January 23, 2012. doi:10.1161/CIR.0b013e31824607ee.