Body mass index (BMI) is a standard metric used in healthcare institutions to determine patient health.
It has been frequently criticized for its simplicity of what being healthy entails while being used for decades as the standard assessment for health based on body size.
Many argue that BMI should not be used in medical or fitness contexts since it is antiquated and incorrect.
Everything you need to know about BMI, its history, whether it accurately predicts health, and its alternatives, is provided on this page.
What is BMI?
Body mass index is referred to as “BMI.” A Belgian mathematician called Lambert Adolphe Jacques Quetelet created the BMI in 1832. (1).
He created the BMI scale to quickly determine a population’s level of overweight and obesity to assist governments in allocating health and financial resources (1).
Interestingly, Quetelet claimed that BMI was better at capturing the general health of a group than using it to investigate a single individual. However, it is frequently utilized to assess people’s health (1).
The BMI scale is based on a mathematical formula that compares a person’s height in meters squared to their weight in kilograms to determine if they have a “healthy” weight (1):
- BMI = weight (kg) / height (m2)
Alternatively, BMI can be calculated by dividing weight in pounds by height in inches squared and multiplying by 703:
- BMI = (weight (lbs) / height (in2)) x 703
Another option is a BMI calculator that is available online, such as the one from the National Institutes of Health.
If you don’t fit the “normal” weight definition, a healthcare expert could advise modifications to your health and way of life.
Certain nations have used this BMI scale to reflect the size and height of their respective populaces accurately. Compared to non-Asians, Asian men and women, for instance, have been proven to have a greater risk of heart disease at a lower BMI (3).
Even though this can offer a healthcare practitioner a quick overview of a person’s health based on weight, it ignores other aspects of a person’s health, including age, sex, race, genetics, fat mass, muscle mass, and bone density.
Is it a good indicator of health?
Most studies demonstrate that a person’s risk of chronic illness and early mortality does rise with a BMI lower than 18.5 (“underweight”) or of 30.0 or above (“obesity”), despite concerns that BMI doesn’t precisely determine if a person is healthy (4, 5).
For instance, a 2017 retrospective analysis of 103,218 fatalities discovered that those with a BMI of 30.0 or above (referred to as “obesity”) had a 1.5–2.7-fold higher chance of dying during a 30-year follow-up (4).
Another research of 16,868 individuals found that those with an “obese” BMI had a 20% higher risk of mortality from all causes, including heart disease, than those with a “normal” BMI (6).
Additionally, the researchers discovered that those with “underweight” BMI and “severely obese” or “very obese” BMI died on average 6.7 years and 3.7 years sooner than people with “normal” BMI (6).
According to other research, a BMI above 30.0 considerably raises the chance of developing chronic conditions such as type 2 diabetes, heart disease, breathing problems, renal illness, non-alcoholic fatty liver disease, and mobility problems (7, 8, 9, 10, 11, 12, 13).
The incidence of metabolic syndrome, heart disease, and type 2 diabetes has also been linked to a 5–10% drop in a person’s BMI (14, 15, 16, 17).
Many health practitioners can use BMI as a broad indicator of a person’s risk because most studies indicate that obese persons have an elevated chance of developing chronic diseases. It should not be the sole diagnostic tool employed (18, 19).
Downsides of BMI
There are many problems with BMI use, despite data linking low (below 18.5) and high (30 or above) BMI with elevated health risks.
Doesn’t consider other factors of health
Without taking into account a person’s age, sex, genetics, lifestyle, medical history, or other considerations, BMI provides a “yes” or “no” answer as to whether they are of “normal” weight.
By ignoring other vital health indicators like cholesterol, blood sugar, heart rate, blood pressure, and inflammatory levels, such as BMI, one may exaggerate or underestimate their natural health.
Additionally, BMI employs the same formula for both sexes despite the differences in the body composition of men and women (men having higher muscle mass and less fat mass than women) (20).
Additionally, a person’s body fat mass rises typically, and their muscle mass gradually reduces as they age. Numerous studies have demonstrated that an older adult’s BMI of 23.0-29.9 can protect against illness and early mortality (21, 22).
A person’s mental health and complex social issues like money, access to inexpensive and nutritious food, food skills and knowledge, and housing conditions are ignored when a person’s health is only determined by their BMI.
Assumes all weight is equal
Muscle is denser and takes up less space even if 1 pound or kilogram of muscle weighs the same as 1 pound or kilogram of fat. As a result, someone who is highly slim but has a lot of power may consider more than average.
For instance, a person with a BMI of 29.5 who weighs 200 pounds (97 kilograms) and is 5 feet 9 inches (175 cm) tall is considered to be “overweight.”
The appearance of two persons of the same height and weight might vary considerably. One can be a bodybuilder with a lot of muscle, while the other might have more fat.
If BMI is the only factor considered, it is pretty easy to mistakenly label someone as “overweight” or “obese” despite their low fat mass. As a result, in addition to weight, it’s crucial to consider a person’s muscle, fat, and bone mass (23, 24, 25).
It doesn’t consider the fat distribution
A higher BMI is associated with worse health outcomes, but body fat distribution may be more critical.
People with a gynoid or pear-shaped body type—those with fat deposited in their hips, buttocks, and thighs—had a lower chance of developing chronic diseases than those with an android or apple-shaped body type (26, 27, 28, 29).
For instance, researchers discovered that individuals with pear-shaped fat distribution decreased the risk of all-cause mortality. In contrast, apple-shaped fat distribution had a considerably greater chance in an analysis of 72 studies that included data from more than 2.5 million people (30).
The authors emphasized that BMI does not consider where fat is deposited in the body, which can lead to incorrect classification of a person as being unhealthy or at risk of disease (30).
It may lead to weight bias
A medical practitioner is supposed to apply their best judgment, which means they will take the BMI result and treat each patient as an individual.
However, some healthcare providers utilize BMI to assess a patient’s health before making recommendations, which can result in weight bias and subpar care (31, 32).
Higher BMI patients frequently claim that their doctors only address their BMI during appointments for unrelated issues. Severe medical conditions often go undiagnosed or are misdiagnosed as weight-related disorders (31).
In reality, research has shown that those with higher BMIs are less likely to have frequent health checks because of anxiety about being assessed, mistrust of the medical staff, or a bad experience in the past. This can result in delayed diagnosis, care, and treatment (33).
It May is not relevant for all populations
Even while BMI is widely used among all people, it could not adequately represent the health of some racial and cultural groups.
In contrast to white people, persons of Asian origin had a higher risk of chronic illness at lower BMI cut-off values, according to multiple research (34, 35, 36).
In truth, the Asian-Pacific BMI recommendations, which offer various BMI cut-off values, were produced by the World Health Organization (2, 37, 38):
BMI range Classification
less than 18.5 kg/m2 underweight
18.5–22.9 kg/m2 normal weight
23.0–24.9 kg/m2 overweight
25.0 kg/m2 or greater obese
According to several research, these alternate cut-off points are more effective in identifying health risks among Asian people. Further study is still required to compare these cut-off points with multigenerational Asian Americans (39, 40, 41).
Black people may sometimes be mistakenly labeled overweight while having more muscle mass and lower body fat. This may imply that the BMI cut-off value for chronic disease risk is more significant for Black women than for persons of other races (35, 42, 43, 44).
A 2011 research indicated that Black women were metabolically fit at cut-off values 3.0 kg/m2 higher than persons who are not Black, which further calls into doubt the value of BMI for all racial and ethnic groups (45).
Last but not least, depending solely on BMI disregards the cultural significance of body size to various communities. Higher fat mass is regarded as desirable and healthier in some cultures. Healthcare practitioners should consider what each person’s definition of “health” is (46, 47, 48).
All medical practitioners must go beyond BMI to provide patient-centered recommendations because major health choices, such as surgical procedures and weight loss therapies, are focused on BMI and weight.
Better alternatives
Because it is practical, affordable, and available in many healthcare settings, BMI is still an effective evaluation tool despite its many shortcomings.
Though each has its own set of benefits and drawbacks, alternatives to BMI exist and may be better indicators of a person’s health (49, 50, 51, 52).
Waist circumference
Definition
More excellent body fat in the abdominal region, linked to a higher risk of chronic illness, is indicated by a bigger waist circumference, one greater than 35 inches (85 cm) for women or 40 inches (101.6 cm) for males.
Benefits
With just a measuring tape, it is simple to measure.
Downsides
It disregards various body forms and builds, such as apple-shaped vs. pear-shaped bodies (e.g., muscle and bone mass).
Waist-to-hip ratio
Definition
A high ratio (more than 0.80 for women and more significant than 0.95 for males) denotes increased abdominal fat deposits and a higher risk of heart and chronic illness.
A low ratio indicates more hip fat storage, linked to improved health (lower than or equal to 0.80 for women and lower than or equal to 0.95 for males).
Benefits
Using simply a measuring tape and calculator, it is simple to measure.
Downsides
It disregards various body forms and builds, such as apple-shaped vs. pear-shaped bodies (e.g., muscle and bone mass).
Body fat percentage
Definition
Body fat percentage measures a person’s relative body fat content.
Benefits
In comparison to BMI, it differentiates between fat mass and fat-free mass and provides a more accurate picture of health risks.
Downsides
Convenient evaluation technologies have a significant chance of inaccuracy, including skinfold assessments, portable bioelectrical impedance analysis, and at-home scales.
More precise equipment (such as dual-energy X-ray absorptiometry, underwater weighing, and BodPod) is costly and beyond of reach for many people.
Lab tests
Definition
Lab tests are different blood and vital signs that can determine the risk of developing a chronic condition (e.g., blood pressure, heart rate, cholesterol, blood glucose levels, inflammation).
Benefits
These tests offer a more thorough analysis of a person’s metabolic health and do not use body fat as the sole indicator of health.
Downsides
A single lab result is frequently insufficient to make a diagnosis or determine risk.
Healthcare practitioners should not depend just on one test, regardless of the evaluation method they utilize. A BMI and waist measurement, for instance, may be taken, and if there is cause for worry, a blood test may be conducted.
It’s crucial to consider each patient individually to understand what health means to them physically, mentally, emotionally, and spiritually.
The bottom line
Body mass index (BMI) is a highly debatable health assessment technique used to determine a person’s risk for ill health and body fat.
According to most studies, as BMI rises over the “normal” level, there is an increased chance of developing a chronic illness. A low BMI (below 18.5) has also been associated with adverse health effects.
However, BMI does not consider other factors that may affect health, including age, sex, fat mass, muscle mass, race, genetics, and medical history. Furthermore, it has been demonstrated that using it as the only predictor of health increases weight bias and health disparities.
BMI is an excellent place to start, but it shouldn’t be the primary indicator of your health.
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