BMI is not an accurate predictor of health because it does not account for body fat percentage or body fat distribution.
In addition, BMI cannot accurately predict the health of different demographics and races because it was created with data from only white Europeans.
Measurements that are more accurate than BMI at predicting health outcomes include blood pressure, waist circumference, and cholesterol levels.
Body mass index (BMI) is one of the most popular ways to measure body composition as it pertains to health. However, research indicates BMI is not the most accurate depiction and can have serious limitations in weight distribution, body fat percentage, and different demographics.
Here is all you need to know about BMI and weight measuring alternatives.
What is BMI?
BMI, or body mass index, is a calculation that estimates a person's body fat by dividing their weight in kilograms by their height in meters squared (BMI = kg/m2). The results are broken down into four categories:
Underweight ( < 18.5)
Normal (18.5 - 24.9)
Overweight (25 - 29.9)
Obese (> 30)
Doctors may use BMI measurements as a screening tool to indicate which category you fall into, and whether you have an increased risk for certain health conditions, such as heart disease or diabetes, based on your results.
BMI was initially created in the 19th century by the Belgian mathematician and statistician Lambert Adolphe Quetelet as a way to measure obesity in the general population.
The formula then evolved through the 1940s when the Metropolitan Life Insurance Company (MLIC) installed an ideal weight standard to determine how much to charge clients for insurance based on their health.
"MLIC developed the idea of a BMI classification to determine what height and weight people had relative to their death," says Fatima Cody Stanford, MPH, an obesity medicine physician and scientist at Massachusetts General Hospital. "But the problem with looking at that historical data is that it did not include the diverse representation of individuals in the United States."
No, BMI is not always an accurate measure of health
While BMI may be a quick, affordable, and easily accessible way to screen for a person's health, the formula is better suited for information about general populations, according to Stanford. When analyzing BMI on the individual level, there are several other factors to consider that BMI does not take into account:
1. BMI does not measure body fat percentage
Body fat percentage (BFP) is the percent of your body that is fat tissue compared to your total body mass. It is normally measured with skinfold calipers, bioelectrical impedance, or most accurately through a DXA X-ray Scan.
One of the main issues with BMI is that it cannot account for the difference between muscle and fat. Because muscle tissue is more dense than fat, many athletes and bodybuilders are considered overweight according to BMI despite being in peak athletic health.
"Body fat percentage will give a better assessment of health because the disease risk is more correlated with body fat rather than body weight," says Chika Anekwe, MD, MPH, an obesity medicine physician at Massachusetts General Hospital and an instructor at Harvard Medical School.
2. BMI does not account for different demographics
When Quetelet originally created BMI, it pulled data from Anglo-Saxon bodies in an entirely European population. Because of this, it is not always an accurate depiction of health for other demographics and races.
For example, researchers found the BMI obesity cut-off for Asian populations actually falls lower than the standard BMI chart. In 2004, the World Health Organization found Asian people with a high risk for type 2 diabetes and cardiovascular disease had lower BMIs.
Another large 2004 study of over 15,000 Chinese adults found that a high risk for cardiovascular disease started at a lower BMI and waist circumference than for Caucasians. This means when screening for BMI, Asian people may have a higher disease risk in categories considered healthy or normal on the BMI chart.
Additionally, Stanford conducted a study in 2020 that found what is considered healthy for Black women is higher than the standard BMI chart, while for Hispanic and white women, what is considered healthy is lower than the chart. For example, when measuring the risk for diabetes, Black women fall closer to 33 and white women average at 29.
"The key thing to get across is to personalize our care for patients," says Stanford. "It's not a one size fits all approach and we can't expect everyone needs to be a BMI of 25. For Black women, for example, you might see someone with a BMI of 32, but that might actually be really healthy for them in the context of their whole profile."
3. BMI does not measure body fat distribution
The specific location of fat is another important factor when considering overall health, and is a measure that BMI does not adjust for. Upper body fat around the midsection and visceral fat are more correlated to health complications, such as cardiovascular disease than lower body fat around the thighs and butt region.
Medical term: Visceral fat is body fat stored around the abdomen and important organs such as the liver, pancreas, and intestines.
"If we have fat in our midsection, it's around our vital organs such as our heart or our liver, which can confer bad risks," says Stanford.
What are more accurate predictors of health?
Anekwe says there are more accurate predictors of health than BMI. These are called the five metabolic risk factors. Together, they can increase your chances of heart disease, stroke, and diabetes.
These measurements include:
Waist circumference: Excess fat around the waist. If your circumference is 35 and over for a woman or 40 and over for a man, you might have increased risk.
General advice: Talk to your doctor if you are concerned about the accuracy of your BMI or looking for different ways to measure your health.
Although measuring body mass index can be a quick and easy way to screen for your health outcomes, there are numerous caveats that BMI does not address, such as different demographics, weight distribution, and body fat percentage.
In order to more accurately understand your health, metabolic factors like blood pressure and waist circumference can better predict your overall risk for certain health conditions.
If you are concerned about BMI or your weight, it's perfectly normal and safe to consult your doctor or a medical professional to better understand what is personally healthy for you and your body.
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