Throughout 2021, Good Housekeeping will be exploring how we think about weight, the way we eat, and how we try to control or change our bodies in our quest to be happier and healthier. While GH also publishes weight loss content and endeavors to do so in a responsible, science-backed way, we think it’s important to present a broad perspective that allows for a fuller understanding of the complex thinking about health and body weight. Our goal here is not to tell you how to think, eat, or live — nor is to to pass judgment on how you choose to nourish your body — but rather to start a conversation about diet culture, its impact, and how we might challenge the messages we are given about what makes us attractive, successful and healthy.
If you’ve been to a doctor, you’re likely familiar with the measure of body mass index (BMI). “The BMI originated in the 1800s as a way to categorize someone into a range of ‘underweight,’ ‘normal weight,’ ‘overweight’ or ‘obese,’” Amy Lee, M.D., an internal medicine physician and weight specialist. However, researchers and physicians are beginning to realize that those weight classifications may not be as helpful as once thought. Here’s everything you need to know about BMI and what it does — and doesn’t — tell you about your health.
Is the BMI an accurate measure of health?
The short answer, not in and of itself. Here’s what the BMI is: “Your BMI is calculated by dividing your weight by your height squared to give you a number of kilograms per meter squared,” says Dr. Lee. According to the Centers for Disease Control and Prevention (CDC):
- A BMI below 18.5 is considered “underweight.”
- A range of 18.5 to 24.9 is “normal or healthy.”
- A range of 25 to 29.9 is “overweight.”
- A BMI of 30 and above is “obese.”
But it turns out that there are some real problems with using these categories as a way to determine a person’s overall health or even body composition.
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First off, “Many people are surprised to learn that people who are ‘overweight’ have lower mortality risk than ‘normal weight’ people, that people who are ‘obese’ have the same mortality risk as ‘normal weight people’ and the mortality risk associated with ‘morbid obesity’ is small,” says Paula Brochu, Ph.D, associate professor in the College of Psychology at Nova Southeastern University.
Second, if a person is labeled “overweight,” it’s often assumed that they are unhealthy. This is often not the case. “One large 2016 study examined people’s cardiometabolic health across the BMI spectrum and found that nearly half of ‘overweight’ people, nearly one-third of ‘obese’ people, and nearly one-fifth of ‘morbidly obese people were metabolically healthy,” says Brochu.
The reverse is also true. ‘“Nearly one-third of ‘normal weight’ people were cardiometabolically unhealthy. The researchers of this study estimated that nearly 75 million adults in the United States have their health misclassified on the basis of BMI.” This misclassification can promote stigma around weight and prevent people from getting the medical care they need, not to mention encourage harmful eating habits.
So why do you get weighed at the doctor’s?
The BMI does provide some information. “BMI will help us do a quick screening to know who is at a higher risk for additional medical problems because as your BMI goes up, the chances of things like type 2 diabetes, obstructive sleep apnea, heart disease, cancer, infertility, depression, back pain and migraines go up,” says Saniea Majid, M.D., FACS, FASMBS, a board-certified obesity specialist and founder of the Weight Loss and Wellness Center in New Jersey.
The main issue is, when people hear that a higher wait is linked to chronic conditions, they tend to assume that being heavy is the reason a person gets sick. Not only is the association between BMI and health a U-shaped curve, notes Brochu, it’s also based on correlational research — not causation. “It could mean high BMI causes the health problem — what is commonly assumed — but it could also be the case that the health problem causes increases in BMI,” explains Brochu.
This seems to be the case with Type 2 diabetes, for example: Weight gain is a symptom of insulin resistance rather than the cause. “It could also be that some third variable such as genetics, stress, discrimination or health behaviors causes both increases in BMI and the health problem,” she says.
The BMI also doesn’t measure body composition
The BMI is a straightforward numeric ratio and doesn’t take into account how any particular body is put together. “Every body is so different in terms of overall structure, sex differences, and cultural differences,” says Dr. Lee, and these factors matter when it comes to determining a person’s health. For example, muscle weighs more than fat, so athletes or someone who is more muscular could be deemed “overweight” by their BMI even though they may be metabolically healthier than someone whose BMI is in the “normal” range with who has less muscle.
On top of that, where you carry weight matters in terms of your health, but the BMI calculation doesn’t consider the shape or structure of your body. Some research has found that CT scans that show extra fat concentrated around your middle are a better predictor of heart attack and stroke than your BMI. Along those same lines, other studies show a bigger waist-to-hip ratio is more closely linked to heart attack risk than BMI, whereas fat in women’s hips and butts don’t seem to harm health.
What’s “healthy” depends in part on your race and ethnic background
The real kicker, though, is that the BMI system, originally known as the Quetelet Index, stems from decades of research that’s been mainly focused on white people. While BMI math is calculated the same way for everyone, research shows the meaning of the resulting number changes depending on your ethnicity.
“The Indian population, for example, we know that their chances of metabolic syndrome like diabetes and heart disease go up at a BMI of 27,” says Dr. Majid. That’s lower than the BMI of 30 that’s associated with the same health issues in Caucasian people. The number is even lower for people of Taiwanese descent, adds Dr. Majid. That means someone might think they’re in the clear with a BMI that’s less than 30 and actually be at serious risk for health issues.
Another potential problem is that if physicians aren’t familiar with these differences between ethnic backgrounds, they might miss an opportunity to give life-saving care to someone they mistakenly believe is metabolically healthy.
So why do doctors still use the BMI?
- Doctors are often pressed for time and the BMI is a quick way to assess the health of a patient: In best-case scenarios, it’s used in combination with testing for blood pressure, pulse, cholesterol, fasting sugars, fatty liver disease and/or body composition, as well as “a conversation based on a patient’s ethnicity, family history, lifestyle, age, activity level and whether they are perimenopausal,” says Dr. Majid. “All these factors go into play to come up with the best plan of what to do next.” Ideally, your BMI should be treated as just one clue to your health — not a definitive factor or diagnosis.
- BMIs are used to inform billing and insurance payments in our healthcare system. Providers attach specific codes to your medical records so that insurance providers know what they’re paying for. The current coding system (known as the International Classification of Diseases, Tenth Revision, or ICD-10) has the BMI baked into it. “There are ICD-10 codes that correlate with the different variations in BMI,” says Dr. Lee. They tend to go along with conditions such as metabolic syndrome, hypertension, diabetes and sleep apnea, she adds.
- The BMI makes it a little easier to do data-focused research. “This is what we call a rough estimate or indicator of health,” says Dr. Lee. “We have used BMI for studies as an indicator. However, it is just one of the data points.” Essentially, it’s cheap and simple to organize research findings according to the BMIs of study participants — but that’s only helpful if people from all backgrounds are included in research (which hasn’t always been the case) since we know the meaning of a person’s BMI changes depending on their ethnicity. It also makes you wonder how difficult it would be to add more data points (like waist-to-hip ratio or body fat percentage) to make results even more accurate.
What does all this mean for you?
When a healthcare system puts too much focus on BMI and weight, patients bear the burden in a number of ways. For starters, people can be denied medical treatments (such as IVF or certain surgeries) because of their BMI. “Weight often becomes the focus of attention, instead of the presenting issue that a person sought out healthcare for,” says Brochu. “People are recommended to lose weight as a cure-all for whatever might ail them, when the research clearly shows that dieting is not effective for weight loss over the long-term, that dieting does not lead to significant health improvements, and that chronic (yo-yo) dieting is a significant risk factor for mental illness and physical disease.”
Brochu gives the example of a patient with knee pain: “If the person is fat, the doctor may diagnose weight as the problem, prescribe weight loss as the treatment, and send them on their way without further diagnostic tests or treatments: But if the person is not fat, they are much more likely to receive scans and treatment at the time of the complaint,” explains Brochu.
Not only does this promote weight-based stigmas in our society, it can discourage people who are labeled “overweight” and “obese” from seeking out medical care in serious situations in the first place, causing both mental and physical damage. “Weight stigma is stressful, which affects physical and mental health as many of the diseases associated with “obesity,” such as cardiovascular disease, diabetes, hypertension and cancer, are actually stress diseases,” says Brochu. It’s a vicious cycle playing on repeat.
“The social stigma is there because of the way we judge others and not understanding overweightness and obesity,” says Dr. Lee. “It takes a lot of empathy and understanding of the condition from the health practitioner.” If you don’t feel comfortable having open and honest conversations with your physician, remember you have every right to ditch them and find a new one. Brochu wishes more doctors adopted weight-inclusive health approaches and that patients knew their bodies are not the problem. “People come in all sizes and that is okay,” she says.
Read More From Our Anti-Diet Series
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