Chances are at some point in your life, you and your doctor have discussed your body mass index (BMI) in relation to your health. Unfortunately, for many people (maybe you, too) these talks can be distressing, considering all the weight that those three little letters carry.
That’s because “the normative approach to healthcare right now is that BMI is one of the distinct measures of health,” says Dr Maria Monge, an eating disorder specialist.. Meaning: Whether your BMI is “too high,” “too low,” or “just right,” it supposedly says a lot about your physical well-being. However, many researchers are now saying that the BMI is actually a rather poor summary of how you’re doing health-wise.
What is the BMI anyway?
Objectively, the BMI is a simple number that represents your weight-to-height ratio. It’s calculated by dividing your weight (in kilograms) by your height (in meters) squared. But this takes on a whole different meaning when you place that number in a health context. Here’s how BMI is currently categorised:
- Underweight is considered having a BMI of 18.5 or below
- Normal is 18.5–24.9
- Overweight is 25–29.9
- Obese is 30 or greater
Experts suggest that your BMI is an estimate of body fat, which if, “too high,” will increase your risk of heart disease, high blood pressure, type 2 diabetes, and certain cancers.
The thing is: This oversimplified narrative encourages many health practitioners to see “excessive” body fat as the direct cause of disease rather than something that may be a correlating factor, according to medical director and psychiatrist Dr Elizabeth Wassenaar. In other words, having a higher BMI does not necessarily mean you’ll experience poor health; there are many factors—independent of weight—that can lead to illness.
“Humans are much more complex than a series of calculations and numbers, and the physiology of health, wellness, and un-wellness are very complicated,” says Dr Wassenaar.
Below, experts explain why the BMI misses the mark as a standard of health and what doctors can do to serve their patients from a weight-neutral perspective.
Why the BMI is not a great measure of health
There are many reasons why the BMI falls short as an overall health assessment. These are the top ones:
The BMI was never designed to measure health
“The formula for BMI originated in 1832 from a Belgian mathematician, Lambert Adolphe Jacques Quetelet, who didn’t intend it for medical use,” says Dr Sylvia Gonsahn-Bollie, the author of Embrace You: Your Guide to Transforming Weight Loss Misconceptions into Lifelong Wellness. Quetelet came up with this weight-to-height calculation in order to figure out the average body size among European men. Thus, the “BMI was created as a population-based assessment, not an individual assessment,” adds Dr Gonsahn-Bollie. “In other words, a BMI chart is a reflection of how much a group of people generally weigh, not what one person ‘should’ weigh.”
There is no clear relationship between BMI and health
There are studies that challenge the idea that being so-called “overweight” or “obese” means you are unhealthy. For example, after analysing data from more than 40,000 participants, US researchers found that nearly half the people classified as “overweight” and more than a quarter labelled “obese” had healthy blood levels of lipids and glucose. This meant they showed no signs of developing conditions like heart disease or diabetes. At the same time, 30% of those labelled “normal-weight” had unhealthy levels of these markers.
Meanwhile, researchers of a 2016 self-reported study discovered that having a higher BMI does not necessarily increase a person’s risk of heart attack. They followed 4,046 pairs of identical twins over the course of 12 years and recorded 203 heart attacks and 550 deaths among the twins with higher BMIs, and 209 heart attacks and 633 deaths among thinner twins. Even those twins with a BMI of 30 or higher (which is technically “obese”), had no increase in heart attack risk.
“What most studies show is that people considered overweight and mildly or moderately obese live at least as long as or longer than people deemed normal weight,” Lindo Bacon PhD, researcher and co-author of Body Respect, said in a recent Youtube vlog. In fact, having a “‘normal’ BMI can create a false sense of stable health and cause other risk markers to be minimized or ignored,” says dietitian Cara Harbstreet.
Overall, “there's no scientific measurement that shows you that fat will kill you or that fat people are unhealthy universally across the board,” says Dr Maggie Landes, an anti-diet doctor and coach.
The BMI doesn’t measure your body fat
It also doesn’t assess your overall composition of fat and muscle, according to Harbstreet. Even if you were to make the conclusion that fat is automatically bad, the BMI doesn’t even measure it well. “It’s believed that this is a reliable measure of body fat, but it is not,” says Harbstreet, as it doesn’t differentiate between fat, muscle mass (which is more dense than fat, by the way, and can make you weigh more), and bone density.
This is the reason why many muscular athletes who are physiologically sound are often labelled as “overweight,” says Dr Landes. Meanwhile, elderly adults—who tend to have less muscle mass and lower bone density due to aging—are labelled as having “normal” BMI, potentially leaving doctors blind to potential red flags, Dr Landes adds. For example, a drop in an older adult’s BMI might be a sign of sarcopenia (excessive loss of muscle), which can increase fall risk and mortality risk.
The BMI does not take into account a person’s age, sex or genes
The BMI weight categories are the same regardless if you are a man, woman, 15, or 75. And yet, your sex, age, and various genetic factors can affect you weight in ways that are not indicative of a health issue, according to Dr Landes. For instance, women naturally tend to have a higher percentage of body fat than men and as a result tend to have higher BMIs. And even though it’s normal “for children between the ages of 3 and 18 to put on weight as they grow, doctors often mistakenly consider them to be obese and therefore “unhealthy.” says Dr Landes.
The BMI can contribute to stigma about weight
It’s not uncommon for people living in fat bodies to feel judged, shamed, and scrutinised when they go to their regular check-ups, according to Dr Landes. Even if someone has come to their doctor about an issue that has nothing to do with their weight—like acne or a sinus infection—oftentimes when the doctor finds their BMI is high, “it colours every aspect of a doctor’s visit,” she says. “Weight is now the problem and it’s a distraction to the conversation on health.” Oftentimes this means that fat people get less quality care than their thinner counterparts.
Not only do fat people get less quality care, stigmatising experiences like these discourage many people from seeking preventative medical treatments for years until they get really sick, adds Dr Landes. Weight stigma, according to some studies, can also cause chronic stress which can impact a person’s heart health. Some researchers believe that these are the real reasons why high BMI correlates with disease.
Better ways to measure health instead of the BMI
Because so much of our healthcare system leans on the BMI to “assess” patients, it’s not going anywhere anytime soon. But luckily, there are plenty of Health at Every Size (HAES)-informed doctors and registered dietitians who are showing that there are less stigmatising and more reliable ways to measure someone’s overall well-being.
“There’s lots and lots of measures we could look at [besides BMI], like blood pressure, resting heart rate, insulin resistance, certain inflammatory markers, sleep hygiene, eating behaviours [...] asking patients about their mental health and food security,” says Dr Landes. “All that stuff is going to impact your health risk and your quality of life.”
Dr Landes argues that combining all of these sorts of tests and asking these questions gives the doctor a fuller picture of a person’s health rather than jumping to clinical assumptions based on someone’s weight. In fact, barring very specific situations—like when someone needs chemotherapy, dialysis, or general anaesthesia—patients don’t need to be weighed to receive quality treatment, she adds.
If you do not want to discuss your BMI with your doctor, you can request that they avoid weight conversations for future appointments and instead order bloodwork (if it hasn’t been ordered already) in order to focus more definitively on health. This can be a tough conversation to have; Dr Monge suggests bringing notecards so you are prepared with what you want to say.
If your doctor does not comply, and you’re able to switch practitioners, you can look at the HAES directory to see if there’s a physician nearby who understands to look at your health in a more holistic way.
Overall, understand that “the BMI harms our ability to truly understand what factors might impact disease and how [doctors] might be able to support people in living healthier, more fulfilled lives,” says Dr Wassenaar. “As doctors, we need to shift our focus on improving an individual’s health rather than on weight loss and emphasise the need to address weight bias, discrimination, and the trauma it can cause people.”
Newsletter
