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Is Body Mass Index (BMI) A Good Measure Of Health?
Published on October 27, 2021 and last updated for accuracy on August 13, 2022
The BMI is a standard health assessment tool in most hospitals.
It has been widely criticized for its oversimplification of what being healthy truly means.
Many argue that BMI is obsolete and should not be used in medical or fitness settings.
This article covers BMI, its history, whether it is a reliable predictor of health, and alternatives.
BMI – Body mass index (BMI) The BMI was created in 1832 by Lambert Adolphe Jacques Quetelet.
He created the BMI scale to help governments allocate health and financial resources.
The BMI was useful for capturing a population’s overall health, according to Quetelet. Nonetheless, it is widely used to assess health.
The BMI scale is based on a mathematical formula that divides a person’s weight in kilograms by their height in meters squared:
BMI = kg/m (m2)
Alternatively, multiply weight in pounds by height in inches squared by 703 to get BMI:
BMI = (weight (lbs) x 703
You can also use an online BMI calculator like the one from the NIH.
After calculating BMI, you compare it to the BMI scale to see if you fall within the “normal” weight range:
Classification by BMI
- Under 18.5 underweight
- 18.5–24.9 normal weight
- 25.0–29.9 overweight
- 30–34.9 obese class I
- 35.0–39.9 obese class II
- >40 extremely obese class III
If you are not in the “normal” weight range, a healthcare professional may suggest health and lifestyle changes.
Some countries use this BMI scale to better represent population size and stature. For example, compared to non-Asians, Asian men and women have a higher risk of heart disease at a lower BMI.
However, it does not take into account factors such as age, gender, race, genetics or fat, muscle, and bone density.
A person’s body fat is estimated using height and weight. Normal BMI is 18.5–24.9.
Is it A Good Health Sign?
Despite concerns that BMI does not accurately assess health, most studies show that a BMI of 18.5 or higher (underweight) increases the risk of chronic disease and premature death.
For example, a 2017 study of 103,218 deaths found that obese people had a 1.5–2.7 times higher risk of death after 30 years.
Another study of 16,868 people found that those with an “obese” BMI had a 20% higher risk of death from all causes and heart disease than those with a “normal” BMI.
The researchers also discovered that those with a BMI of “normal” died 6.7 years earlier than those with a BMI of “underweight”.
Difficulty breathing, kidney disease, non-alcoholic fatty liver disease, and mobility problems are all linked to a BMI over 30.
A 5–10% reduction in BMI has also been linked to lower rates of metabolic syndrome, heart disease, and type 2 diabetes.
Obesity has been linked to an increased risk of chronic diseases, so many health professionals use BMI as a general indicator of risk. But it shouldn’t be the only one.
Most research supports BMI’s ability to estimate one’s risk of chronic disease, especially early death and metabolic syndrome weight with a low risk of poor health, while anything above or below may indicate a higher risk of poor health.
Other Health Factors Are Ignored
BMI only indicates whether a person is “normal” weight without regard to age, sex, genetics, lifestyle, medical history, or other variables.
The BMI alone may miss important health indicators like cholesterol, blood sugar, heart rate, blood pressure, and inflammation, and may over or underestimate a person’s true health.
Even though men have more muscle mass and less fat mass than women, BMI uses the same calculation for both groups.
Plus, as we age, our body fat mass increases and our muscle mass decreases. Many studies have shown that a BMI of 23.0–29.9 in older adults can help prevent disease and death.
Finally, using BMI to assess health ignores mental health and complex socioeconomic factors like income, access to affordable and nutritious food, food skills and knowledge, and living environment.
Assume Equal Weight
Muscle weighs the same as fat, but it is denser and takes up less space. So a person who is lean but has many muscle mass may be heavier.
A 200-pound (97 kg) person standing 5 feet 9 inches (175 cm) tall has a BMI of 29.5, indicating “overweight”.
People of the same height and weight can look very different. One may be a bodybuilder with many muscle, while the other has more fat.
If only BMI is used, a person could be misclassified as “obese” despite having a low-fat mass. So, in addition to weight, consider a person’s muscle, fat, and bone mass.
Omits Fat Distribution
The location of fat on the body may be more important than BMI.
The android or apple-shaped body type has a higher risk of chronic disease than the gynoid or pear-shaped body type.
Those with an apple-shaped fat distribution had a significantly higher risk of all-cause mortality, while those with a pear-shaped fat distribution had a significantly lower risk.
The authors point out that BMI does not account for body fat distribution, which can misclassify a person as unhealthy or disease-prone.
Causes Weight Bias
A doctor is expected to use their best judgment, which means interpreting the BMI result while considering the patient as an individual.
However, some doctors only use BMI to assess a patient’s health, which can lead to weight bias and substandard care.
In appointments for unrelated issues, those with higher BMIs report doctors focusing solely on their BMI. Serious medical issues often go unnoticed or are misdiagnosed as weight issues.
Studies show that people with higher BMI are less likely to get regular health checks due to fear of being judged, distrust of healthcare professionals, or previous bad experiences. Diagnoses, treatments and care can all be delayed.
Not Applicable to All Populations
Despite widespread use among adults, BMI may not accurately reflect certain racial and ethnic groups’ health.
For example, compared to whites, Asians have a higher risk of chronic disease at lower BMI cut-off points.
The WHO developed Asian-Pacific BMI guidelines with alternate cut-off points.
Several studies have found that these alternative cut-off points better identify Asian health risks. Research on these cut-off points in multi-generational Asian Americans is needed.
And black people may be misclassified as obese despite having less fat and more muscle. This may indicate that Black women have a higher risk of chronic disease than other races.
One 2011 study found that Black women had metabolically healthy cut-off points 3.0 kg/m2 higher than non-Black women, raising questions about the utility of BMI for all races and ethnicities.
Finally, relying solely on BMI ignores the cultural significance of body size. In some cultures, having more fat mass is considered desirable. They should consider what “health” means to each person.
The fact that major health decisions like surgery and weight loss interventions are based on BMI and weight means that all health professionals must go beyond BMI to make patient-centred recommendations.
BMI measures only a person’s weight and height, not their health. Age, sex, race, body composition, and medical history all influence weight and health.
BMI is still used despite its many flaws because it is convenient, affordable, and accessible in all healthcare settings.
Other measures of a person’s health besides BMI exist, each with its own set of benefits and drawbacks.
1. Waist circumference
A waist circumference of 35 inches (85 cm) for women and 40 inches (101.6 cm) for men indicates more abdominal fat, which is linked to a higher risk of chronic disease.
It’s easy to measure with a tape measure.
It ignores body types (apple-shaped vs. pear-shaped) and builds (e.g., muscle and bone mass).
A high ratio (over 0.80 for women and over 0.95 for men) indicates abdominal fat storage and is linked to an increased risk of heart and chronic disease.
A low ratio (below or equal to 0.80 for women and 0.95 for men) indicates more hip fat storage and better health.
It’s easy to measure with a tape measure and a calculator.
It ignores body types (apple-shaped vs. pear-shaped) and builds (e.g., muscle and bone mass).
3. Body fat %
Body fat percentage measures a person’s relative body fat.
It distinguishes between fat and lean mass and represents health risk better than BMI.
Simple assessment tools (like skinfold measurements, bioelectrical impedance analysis, and home scales) are prone to error.
Expensive tools (like dual-energy X-ray absorptiometry, underwater weighing, and BodPod) are out of reach for many.
4. Tests in the lab
Lab tests measure blood and vital signs to assess chronic disease risk (e.g., blood pressure, heart rate, cholesterol, blood glucose levels, inflammation).
These tests provide a more detailed review of a person’s metabolic health than body fat alone.
A single lab value rarely diagnoses or indicates risk.
It’s critical that healthcare professionals don’t rely on just one test. If a person’s BMI and waist circumference are high, a blood test may be ordered.
It’s critical to treat each patient as an individual to determine their definition of health.
Waist circumference, body fat percentage, and blood tests can all be used instead of BMI. But each has its own benefits and drawbacks.
The body mass index (BMI) is a controversial health assessment tool used to assess a person’s body fat and health risk.
Chronic disease risk increases with BMI above the “normal” range. A BMI below 18.5 is also linked to poor health.
However, BMI ignores factors like age, gender, fat mass, muscle mass, race, genetics, and medical history. The use of BMI alone to assess health has been shown to increase weight bias and health inequity.
Though BMI is a good starting point, it should not be your only indicator of health.
How Useful is Body Mass Index (BMI)?
Know your BMI? As with cholesterol, people increasingly know theirs.
If you don’t know your BMI, use an online BMI calculator like this one from Harvard Health Publishing. Just your height and weight. You can also calculate it using this formula:
BMI = (weight x 703) / (height in inches x height in inches).
Is it worth knowing your BMI now? What will you do with it?
Understanding your BMI helps to know what it measures and why it measures it.
The BMI calculates your size based on your height and weight. My mother used to use charts where you had to measure yourself to find your “ideal weight” from choices listed under small, medium, or large “frame” sizes.
These graphs are actuarial statistics, which use data from thousands of people to calculate your likelihood of living a long life. Easy to use, but not clear how to determine “frame size.”
In a similar way, BMI measures your height and weight as a single number independent of frame size. BMI is a relatively new health measure despite its 200-year origins.
A BMI of 18.5 to 25 is considered normal; 25 to 30 is considered overweight; and 30 or more is considered obese. A BMI of 18.5 or less is considered underweight.
Like most health tests, BMI isn’t perfect. Pregnancy or high muscle mass can affect results, and it may not be appropriate for children or the elderly. So, why is BMI important? In general, the higher your BMI, the greater your risk of developing obesity-related diseases like
arthritis, liver disease, and cancer (such as those of the breast, colon, and prostate)
Hypertension, hypercholesterolemia, sleep apnea
The WHO estimates that nearly three million people die each year from obesity. Moreover, people with high BMIs often report feeling better physically and psychologically after losing weight, regardless of disease.
Should We Stop Valuing BMI So Highly?
Maybe. According to research, BMI misclassifies metabolic health, which is linked to body fat and how it is distributed. Moreover, BMI is unreliable in pregnant women, athletes, and the elderly.
This shouldn’t be a surprise. A single measure of BMI, cholesterol, blood sugar, or blood pressure would not be expected to identify cardiovascular health or illness. It’s not the only indicator of health! For example, the above study did not consider conditions like liver disease or arthritis that may be relevant to people with high BMI. And BMI may be better at predicting future health than current. Studies like this and this show that healthy people who are overweight or obese are more prone to diabetes and other health issues.
Dietary guidelines for adults are based on BMI. However, body composition varies by race and ethnicity. So BMI may help predict health status in whites, but not in other racial and ethnic groups.
For example, defining obesity by BMI tends to overestimate risk in Blacks while underestimating risk in Asians. This may lead to inadequate counseling and treatment, increasing healthcare disparities. The World Health Organization and the NIH recommend different BMI cutoffs for Asians. Changes may be recommended for other groups in the future as BMI research evolves.
BMI is clearly not a perfect health indicator. But it’s still a good place to start for conditions that are more common in overweight or obese people. I think knowing your BMI is a good idea. But it’s also vital to acknowledge its flaws.
Is BMI A Good Body Fat Measurement?
Despite its widespread use, the BMI method of body measurement is increasingly viewed as flawed.
A high BMI can also be used to screen for certain weight levels that may lead to health issues. Despite its widespread use, it is not a true indicator of body fatness or overall health.
As most fitness enthusiasts know, BMI is not a perfect measurement. The BMI measurement often overestimates or underestimates a person’s body fat. When it does, it means it.
Which BMI is Wrong?
People often criticize BMI for not distinguishing between body fat and muscle mass, which is important because muscle weighs more than fat.
Former Olympians Usain Bolt and Michael Phelps are two examples of this misinterpretation, according to BMI’s Blind Spots analysis. Also, NFL quarterback Tom Brady is obese according to his BMI. Also, Lebron James of the NBA and Phil Kessel of the NHL both have a BMI of 27.5, which is considered overweight.
Imagine a sprinter who is 6′ tall and weighs 211 lbs. Their BMI would be 28.
Muscle weighs about 18% more than fat.
So the sprinter is heavier than the sedentary person. As previously stated, a glob of muscle weighs roughly 18% more than a glob of fat, so this is clearly not accurate.
What causes this odd error? Imagine a sedentary six-foot-tall 203-pounder. Their BMI would be 27.
BMI fails in other areas as well. The BMI is also unreliable in older adults who have lost muscle and bone mass. In this case, an elderly person’s BMI may be normal but they are overweight.
Also, the BMI calculation is based on Caucasian body types and may not be appropriate for other ethnicities. Asians appear to have 4% more total body fat than white Europeans with the same BMI. Abdominal obesity is common in South Asians, which can affect BMI.
Can BMI Affect Health?
A person with an unhealthy BMI is considered unhealthy, whereas someone with a normal BMI is considered healthy. But according to 2016 research, this isn’t true for 75 million Americans.
The study found that while 54 million Americans were classified as overweight or obese, other cardiometabolic tests (blood pressure, blood sugar, cholesterol, etc.) revealed they were in excellent health. Other cardiometabolic measures later determined that another 21 million people were unhealthy despite having a normal BMI.
The researchers looked at data from the National Health and Nutrition Examination Survey and found that BMI misclassified people’s health at both ends of the weight spectrum.
Others argue that even if someone appears to be overweight but healthy, the extra weight increases their risk of developing certain diseases as they age. So there is some division.