News reports about obesity are abundant, but imbedded in their expansive tales are often conflicting statistics claiming that rates are rising, declining, stabilizing; going up in women, down in men and vice versa, etc. A perspective in the New England Journal of Medicine this week provides an explanation for the inconsistent reporting on the obesity epidemic in the U.S.
Data sources:
The three most often cited surveys are all administered by the Centers for Disease Control (CDC) and have contradictory results:
- The 2009 Behavioral Risk Factor Surveillance System (BRFSS) reported that obesity rose by 1.1% between 2007 and 2008
- The Youth Risk Behavior Survey (YRBS) for high-school students reported that between 1999-2007, significant increases occurred in the percentage of students who were obese (10.7%-13.0%) and overweight (14.4%-15.8%).
- The 2007–2008 National Health and Nutrition Examination Survey (NHANES)reported that obesity rates among adults and children are not rising but have remained stable over the past five to 10 years.
Data Collection Methods:
Differences in data collection may account for incongruous obesity stats. BRFSS and YRBS rely on self-reported height and weight, while the NHANES relies on actual measurements.
Because people have a tendency to lie about their weights on questionnaires, one would assume the self-reported data would be slightly skewed towards the tall and skinny, but that is not the case. The NHANES study, the only one of the three that uses objective data, shows that obesity rates remained constant over the past 10 years.
Are obesity rates truly staying constant?
It is hard to know. While the NHANES has a more reliable study design, it has a much smaller sample size than the other surveys, n=5000 verses the BRFSS n=350,000. The small sample size limits the survey’s sensitivity, which means it may be misrepresenting the true effect.
The authors, Jack and Susan Yanovski of the National Institutes of Health, offer a hopeful view of the situation, citing other research that shows childhood obesity rates are in decline. If obesity rates are slowing, the authors attribute efforts by clinicians, governments, community organizations and industry who have been fighting the environmental causes of the obesity crisis. They also say it is possible that the obesity epidemic has reached a saturation point in which all those who are susceptible to gaining weight are already obese; while the people with natural resistance to weight gain remain thin.
The authors also offer a pessimistic view that statistics do not take into account the people becoming extremely obese with a BMI ≥40. While it is possible the incidence of newly obese people is slowing, the numbers of people becoming morbidly obese is climbing and not being accounted for in these studies.
Rejoice or bemoan?
The Yanovski’s conclude the article with a warning; there are too many obese people in the U.S. Children represent the most worrisome population affected, and are now experiencing record levels of “adult” diseases like diabetes and hypertension.
Higher instances of gestational diabetes have enduring effects on the population because of the risks of predisposing babies for metabolic diseases and causing epigenetic changes that will extended into future generations – creating a vicious cycle.
In Massachusetts, about half of all adults are obese and one third of all children. Governor Deval Patrick launched Mass in Motion in 2009, a state based initiative to combat the obesity problem.
One of the first steps in the program was to gather BMI data on all school children in the state. The preliminary study was released in September of 2010 and found a lot of variation across the school districts. In an earlier article I reported on obesity statistics by town, see that article on childhood obesity here. See here for the full report on childhood obesity in Massachusetts.
March is National Nutrition Month and in honor of this I will be exploring the topics of nutrition and healthy weight loss this month.
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