As Obesity Measures Gain Prevalence, Limitations Exist for Policymaking

Both doctors and public officials are aware of the limitations created by using body mass index to define obesity, which is now considered a disease. But no clear alternative has emerged.
by | July 17, 2013 AT 3:30 AM

The American Medical Association (AMA) made headlines last month when it designated obesity as a disease, a decision not without controversy that’s expected to focus more attention on the issue.

More than a third of Americans are currently considered obese. By 2018, one study projects the number to grow to an alarming 43 percent of the population.

For decades, defining obesity as a measure of body mass index, or BMI, has served as the rule of thumb in evaluating populations’ body fatness. But as the issue gains prominence, both doctors and public officials are keenly aware of the limitations inherent in this methodology.

In determining whether an adult is overweight or obese, doctors calculate BMI based on height and weight. Many have long argued that this simple computation misclassifies some individuals, particularly muscular or athletic types.

By labeling obesity as a disease, AMA’s House of Delegates rejected the recommendation of its own subcommittee studying the issue. AMA’s Council on Science and Public Health pointed out limitations of BMI in its report, calling for a “better measure of obesity than BMI alone.”

“Without a single, clear, authoritative, and widely-accepted definition of disease, it is difficult to determine conclusively whether or not obesity is a medical disease state. Similarly, a sensitive and clinically practical diagnostic indicator of obesity remains elusive,” the report said.

When assessing an individual’s body fat, doctors have several tools at their disposal. On the public policy side, though, officials widely view BMI as the best measure currently available.

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“It’s just an indicator, and you need to look at other measures behind it to know what’s truly going on,” said Paul Jarris, executive director of the Association of State and Territorial Health Officials (ASTHO).

Policymakers, Jarris said, should monitor not only overall rates of obesity, but data for smaller regions and specific demographic groups as well.

Nearly half of non-Hispanic blacks are considered obese, for example, compared to 34 percent of non-Hispanic whites.

Some argue in favor of establishing different classifications for certain racial and ethnic groups. One of the more frequent calls is for lowering Asians’ BMI cutoff points. Earlier this month, the U.K.'s National Institute for Health and Care Excellence revised its guidelines, setting stricter targets for British Asians.

The current standard BMI classifications used by National Institutes of Health and World Health Organization are as follows (if you’d like to know your own BMI, try using NIH’s handy BMI calculator):

Underweight: < 18.5

Normal: 18.5 – < 25

Overweight: 25 – < 30

Obese – Grade 1: 30 – < 35

Obese – Grade 2: 35 – < 40

Obese – Grade 3: > 40

An earlier report by AMA’s Council on Science and Public Health examining body composition and fat distribution among varying demographic groups also stated BMI misclassifies some people.

The federal government does interpret BMI differently for children and teenagers, factoring in age and gender to account for changes in body fat.

Minnesota Commissioner of Health Ed Ehlinger said officials must avoid demonizing those considered obese.

When assessing the merits of obesity studies, Ehlinger said they should also closely examine survey questions and methodologies. This is particularly crucial when comparing areas on opposite ends of the demographic spectrum.

Alternatives to BMI exist, but they’re all subject to inherent weaknesses. For one, these other methods are far more costly. BMI is also most practical for large-scale surveys.

Dr. David Freedman, an epidemiologist with the Centers for Disease Control and Prevention, said recent research has explored skinfold thicknesses, waist circumference and dual-energy X-ray absorptiometry estimates of body fatness, but no clear consensus has emerged.

“Everyone involved in obesity research realizes that BMI is very crude, but it's proved to be difficult to replace BMI with some equivalently simple measure that can be standardized across observers,” he said.

BMI originated in the 1850s. The federal government last lowered its threshold for the “overweight” classification range in 1998.

Rather than focus solely on obesity, multiple studies present comprehensive health and wellness assessments. Ehlinger cited United Health Foundation’s America’s Health Rankings as one useful report. The University of Wisconsin and Robert Wood Johnson Foundation also publish annual county health rankings (view scores for each county here).

In New Orleans, the health department is focusing its efforts squarely on the city’s fitness and nutrition.

For its primary outcome measure, the city utilizes the American College of Sports Medicine’s American Fitness Index, a broad assessment of numerous health and fitness variables across communities.

Health Commissioner Karen DeSalvo said the fitness index is more reflective of what’s happening on the ground in the city than its obesity rate, which is among the nation’s highest.

“It’s not quite as clear that losing weight does all the things that being physically active does,” she said.

What’s more, DeSalvo said not playing up obesity helps to minimize the stigma that’s associated with the term. “For us, it’s more about the physical fitness pieces and less about the label of obesity.”

While the AMA’s decision carries no legal authority, it may very well prompt doctors and insurance companies to treat the condition differently.

Many local agencies transitioned away from providing cholesterol, blood pressure and other screenings in recent years as grant dollars dried up. With the designation, more insurance companies may opt to partner with health agencies to again offer these services at public clinics, said Truemenda Green, director of healthy communities and chronic disease for National Association of County and City Health Officials.

“It opens the door of possibilities for public health agencies,” Green said.

ASTHO’s Jarris said the effects of AMA’s decision are not yet clear.

“If the result of the AMA’s decision is that insurance begins to cover obesity counseling and treatment, that is positive. However, treating obesity with counseling, drugs and surgery alone will do little to affect the underlying causes of our obesity epidemic. Without sound policy and public health solutions to improve our obesogenic environment and culture we will not bend the curve on obesity,” he said.

State Obesity Rates

The map below shows adult obesity prevalence for states, as measured by 2011 CDC data. Please zoom out to view Alaska and Hawaii.

Obesity Prevalence (%)
< 24% < 28% < 32% 32%+