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Body Mass Index Is Not a Good Measure of Your Health

by A. Janet Tomiyama, Ph.D. and Jeffrey M. Hunger, M.A.

Note: This piece, with slight modifications, originally appeared in Zócalo Public Square.

You’ve just returned from your morning run and you’re rustling through your snail mail when you receive some shocking news—an official memo from your employer informing you that your health insurance premium is increasing by 30 percent. You’ve been deemed a health risk, and you are being charged accordingly.

Yet you’re the picture of health: A run is part of your daily routine, you passed your last physical with flying colors, and kale is your favorite food. This must be some sort of mistake. But you read the fine print to discover that your employer has decided that the most accurate measure of your health is your Body Mass Index, or BMI, which is derived by a formula that compares your weight to your height.

Even though you’re a paragon of health, at 5 foot 2 inches and 164 pounds, your BMI places you within a range considered “obese.” So your insurance company and your employer have determined that you are no longer among the “healthy.”

This may sound Orwellian, but the federal government is working to make it common. Recently proposed rules by the U.S. Equal Employment Opportunity Commission (EEOC) would set clear guidelines for employers to use metrics like BMI to charge higher-BMI employees more for their health insurance. The apparent goal of these rules is to get higher-BMI employees to reduce their weight; a standpoint based on the assumption that such individuals must uniformly face poor health. Our research, however, suggests that this assumption is flawed and these rules will not accomplish this goal. In fact, the proposed rules could yield the opposite results.

BMI is a problematic metric. It was invented more than 200 years ago by a Belgian mathematician named Quetelet, who based it on what he called the “average” human: a white male in Europe in the early 1800s. BMI also gets human biology wrong—it fails to distinguish between bone, muscle, or fat. You’ve probably heard about athletes, including the starting lineup of the Super bowl champion Denver Broncos, being “obese” by BMI standards, even though they’re very obviously in great shape. National Public Radio called the BMI formula “mathematical snake oil”!

As psychological scientists who study health, we were well-versed in the pitfalls of BMI. We knew we had to push back and illustrate the fallacy of this thinking in such a way that policymakers would understand just how many healthy people would be adversely affected.

In a stroke of good fortune rarely seen outside the movies, we found the perfect dataset. The National Health and Nutrition Examination Survey (NHANES) is a nationally representative sample of Americans surveyed every two years about their health and BMI. NHANES allowed us to look at established health markers to see who was healthy, and then see how many of those healthy folks actually fell in the higher-BMI categories employers deem “unhealthy.”

Our next challenge was to come up with an ironclad definition of “healthy.” For our analysis to have credibility, we had to have a definition that would be difficult to attack on scientific grounds. We dove into the research literature to look for different definitions and found quite a few, so we chose the definition that set the highest bar for health and used six different metrics including blood pressure, blood sugar, and cholesterol. These index the health of a person’s heart and blood vessels, risk for diabetes, and inflammation.

After crunching the numbers, the results were stunning. BMI did not map onto the real markers of health. Some 34.4 million of the 70 million-plus Americans categorized as “overweight” by BMI were perfectly healthy. That’s 47 percent! The chances of BMI being a good predictor were not much better than flipping a coin. And 29 percent of Americans rated “obese” under BMI were healthy as well. Add those numbers together—and it means that more than 54 million healthy Americans would be unfairly penalized under the EEOC rules.

Our analysis uncovered another pitfall of BMI: 21 million individuals in the “normal” BMI range—those who would be considered perfectly healthy by employers and insurance companies—were actually unhealthy according to the criteria. These are people who would likely have higher health costs but who would skate by without added penalties under the new EEOC rules. More alarming, the fallacious assumption that “normal” BMI individuals are healthy could mean they wouldn’t get preventive care or that important diagnoses could be delayed or missed altogether.

Clearly, BMI needs to go. We hope our analysis is the final nail in the coffin for this flawed measure.

But the obsession with BMI is really a symptom of a larger issue: a national infatuation with weight that not only affects how people in power define health, but also perpetuates an entrenched stigma against heavier people. We’ve run many studies in our labs showing that this weight stigma gives rise to situations that make it hard for people to be healthy. We’ve shown, for example, that experiencing weight stigma makes individuals eat more high-calorie snack foods and feel less confident in their ability to maintain a healthy diet. These are things that are bad for you no matter what you weigh.

We’ve also found that people who experience weight stigma have higher levels of the stress hormone cortisol. That’s a problem because cortisol increases a person’s drive to eat foods high in sugar, fat, and calories and sends a signal to the body to start storing visceral fat. That’s a type of fat that sticks to your organs and won’t necessarily make your body bigger, meaning it flies under the radar of BMI. It’s also the type of fat that increases your risk for diabetes and cardiovascular disease.

Our cultural obsession with weight has led us to misguidedly prioritize numbers on the scale over important modifiable health behaviors—eating, exercise, and sleep. Beyond leading us astray from health, this obsession perpetuates the stigma attached to heavier bodies, which is itself an impediment to health.

The evidence is clear: It’s well past time to forget about weight, both as a marker of person’s health and as a marker of a person’s standing in society.

Janet Tomiyama, Ph.D., is an Assistant Professor in the Department of Psychology at the University of California, Los Angeles. She received her B.A. in Psychology in 2001 from Cornell University, and her M.A. and Ph.D. in Social Psychology with concentrations in Health and Quantitative Psychology in 2009 from the University of California, Los Angeles. In 2011. She completed a Robert Wood Johnson Health and Society Scholar Fellowship jointly at the University of California, Berkeley and the University of California, San Francisco. Her research centers around eating, dieting, stress, and weight stigma. See more at

Jeffrey M. Hunger, M.A., is currently a doctoral candidate at the University of California, Santa Barbara where he is working in Dr. Brenda Major’s Self and Social Identity Lab. He also works with Dr. Tomiyama in her Dieting, Stress, and Health Lab at the University of California, Los Angeles. Broadly speaking, his research uses insights from social and personality psychology to understand and improve health and wellbeing. He is particularly interested in the mechanisms by which social and structural conditions (e.g., stigma and discrimination) can undermine health and contribute to group-based health disparities. Much of his current research is focused on testing and refining a theoretical model linking weight-based stigma to poor mental and physical health. See more at

Are you “obese” according to your BMI but perfectly healthy? There is a HERO among us!

Join UCLA’s HEalth Registry of “Obesity” (HERO) and be part of a research study investigating your thoughts, feelings, behaviors, and health.

With your help, the results of this research may help us to understand how everyone – no matter what they weigh – can enjoy good health.

Compensation of up to $100 is provided for your time.

For further information please visit

We note that “obesity” in the title of our study is with the understanding that “obesity” is not an accurate indicator of disease. Indeed, the purpose of HERO is to show that people can be healthy regardless of what number shows up on the scale.

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