Body mass index (BMI) is a typical health assessment measure used in the majority of healthcare settings. Though it has been widely used as the go-to indicator for health based on body size for decades, it has been severely challenged for the oversimplification of what it truly means to be healthy.
Medically reviewed by Dr K on 30th May 2022.
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Is BMI A Good Predictor Of Health?
Body mass index (BMI) is a typical health assessment measure used in the majority of healthcare settings.
Though it has been widely used as the go-to indicator for health based on body size for decades, it has been severely challenged for the oversimplification of what it truly means to be healthy.
Indeed, many argue that BMI is out of date and misleading and that it should not be utilised in medical or fitness contexts.
This article covers all you need to know about BMI, including its history, accuracy as a predictor of health, and alternatives.
Source - Cleveland Clinic Health Essentials
What is BMI?
The term “BMI" stands for “body mass index." Lambert Adolphe Jacques Quetelet, a Belgian mathematician, invented the BMI in 1832.
He created the BMI scale to help governments determine where to concentrate health and financial resources by swiftly estimating the prevalence of overweight and obesity in a particular population.
Surprisingly, Quetelet argued that BMI was not beneficial for analysing single individuals, but rather for providing a picture of a population’s general health. Nonetheless, it is commonly used to assess people’s health.
The BMI scale is based on a mathematical formula that divides a person’s weight in kilogrammes by their height in metres squared to assess if they are of “healthy" weight:
BMI is calculated as follows:
- BMI = weight (kg) / height (m2)
BMI can also be determined by dividing one’s weight in pounds by one’s height in inches squared and multiplying by 703:
- BMI = (weight (lbs) / height (in2)) x 703
You may also utilise an online BMI calculator, such as the National Institutes of Health.
Once your BMI has been computed, it is compared to the BMI scale to establish whether you are within the “normal" weight range:
If you do not fit into the “normal" weight range, a healthcare professional may recommend health and lifestyle adjustments.
This BMI scale has been implemented by several countries in order to better portray the size and height of their people. Asian men and women, for example, have been demonstrated to be at a greater risk of heart disease at lower BMIs than non-Asian men and women.
Though this can provide a medical practitioner with a glimpse of a person’s health based on weight, it does not take into account other characteristics such as age, gender, race, genetics, fat mass, muscle mass, and bone density.
Body mass index (BMI) is a metric that uses height and weight to measure a person’s body fat. A BMI of 18.5–24.9 is considered “normal" and associated with a low risk of health problems, however, anything above or below may suggest a greater risk of developing chronic diseases.
Is It A Reliable Health Indicator?
Despite concerns that BMI may not precisely determine whether a person is healthy, most studies suggest that a BMI less than 18.5 (“underweight") or higher than 30.0 (“obesity") increases a person’s risk of chronic illness and early mortality.
A 2017 retrospective research of 103,218 fatalities, for example, showed that those with a BMI of 30.0 or above (“obesity") had a 1.5–2.7 times higher risk of mortality after a 30-year follow-up.
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.
The researchers also discovered that people in the “underweight" and “severely obese" or “extremely obese" categories died 6.7 and 3.7 years sooner, respectively, than those in the “normal" BMI category.
Other research has shown that a BMI higher than 30.0 increases the risk of chronic health problems such as type 2 diabetes, heart disease, breathing difficulties, renal illness, non-alcoholic fatty liver disease, and mobility concerns.
Furthermore, a 5–10% drop in BMI has been linked to lower risks of metabolic syndrome, heart disease, and type 2 diabetes.
Because most studies reveal a heightened risk of chronic diseases in those who are obese, many health practitioners may use BMI as a basic assessment of a person’s risk. However, it should not be utilised as the only diagnostic tool.
Though BMI has been chastised for simplifying health, the majority of studies support its capability to identify a person’s risk of chronic illness, notably the risk of early mortality and metabolic syndrome.
The Negative Effects of BMI
Despite evidence linking a low (less than 18.5) and high (30 or above) BMI to increased health risks, there are significant problems in its use.
Does Not Consider Other Aspects Of Health
BMI just provides a “yes" or “no" response as to whether a person is of “normal" weight, with no regard for age, gender, genetics, lifestyle, medical history, or other variables.
Using BMI alone could overlook other essential health indicators, such as cholesterol, blood sugar, heart rate, blood pressure, and inflammatory levels, and it may exaggerate or underestimate a person’s genuine health.
Furthermore, despite the fact that men and women have different body compositions — males have greater muscle mass and less fat mass than women – BMI employs the same formula for both groups.
Furthermore, as a person ages, their body fat mass normally grows while their muscle mass gradually decreases. A higher BMI of 23.0–29.9 in older adults has been proven in several studies to be preventive against early mortality and diseases.
Finally, relying just on BMI to define a person’s health overlooks other elements of health, such as mental well-being and complex socioeconomic issues including income, access to inexpensive and healthy meals, food knowledge and skills, and living situation.
Assumes That All Weights Are Equal
Despite the fact that one pound or kilogramme of muscle weighs the same as one pound or kilogramme of fat, muscle is denser and takes up less space. As a consequence, a person who is extremely slim yet has a lot of muscular mass may weigh more.
A 200-pound (97-kg) individual who is 5 feet 9 inches (175 cm) tall has a BMI of 29.5, indicating that they are “overweight."
Two individuals of the same height and weight, on the other hand, may seem radically different. One could be a bodybuilder with a lot of muscular mass, whereas the other could have a lot of fat.
If only BMI is used, a person could be misclassified as “overweight" or “obese" while having a low-fat mass. As a result, in addition to weight, it is critical to examine a person’s muscle, fat, and bone mass.
Does Not Assess Fat Distribution
Though a higher BMI is associated with worse health outcomes, the positioning of fat on the body is more important.
Those with fat deposited around their stomach, referred to as android or apple-shaped body types, are at a higher risk of chronic diseases than those with fat stored in their hips, buttocks, and thighs, referred to as gynoid or pear-shaped body types.
For example, in a study of 72 studies involving more than 2.5 million individuals, researchers discovered that those with apple-shaped fat deposits had a considerably greater risk of all-cause death. Still, those with pear-shaped fat distribution had a reduced risk.
Indeed, the authors emphasised that BMI does not consider where fat is deposited on the body, which might misclassify a person as sick or at risk of illness.
This Might Result In A Weight Bias
It is anticipated that medical professionals would exercise their best judgement, which means that they will take the BMI result and assess their patient as an individual.
However, some health providers exclusively use BMI to assess a person’s health before making medical advice, which can result in weight bias and poor quality treatment.
Those with higher BMIs are more likely to report that their doctors concentrate only on their BMI, even if their visit is for a completely unrelated reason. Serious medical conditions are sometimes overlooked or misdiagnosed as weight-related issues.
Indeed, studies have shown that the higher a person’s BMI, the less likely they are to attend regular health examinations due mainly to fear of being evaluated, mistrust of healthcare professionals, or a past poor experience. This can result in delayed diagnosis, treatment, and care.
It Is Possible That This Is Not Applicable To All Populations
Despite the fact that BMI is widely used among all people, it may not correctly represent the health of particular racial and cultural groups.
Numerous studies, for example, have shown that people of Asian heritage had a higher risk of chronic diseases at lower BMI cut-off values than white people.
In fact, the World Health Organization created Asian-Pacific BMI recommendations that provide various BMI cut-off values.
Numerous studies have found that these alternate cut-off points are more effective in identifying health problems in Asian populations. More study is required to compare these cut-off points with multigenerational Asian Americans.
Furthermore, despite having lower fat content and greater muscle mass, Black persons may be misclassified as overweight. This might imply that chronic disease risk arises at a greater BMI cut-off point in Black women than in other races.
For example, one 2011 research discovered that Black women were deemed metabolically fit at cut-off values 3.0 kg/m2 higher than non-Black people, calling into doubt the use of BMI for all racial and ethnic groups.
Finally, depending just on BMI disregards the cultural significance of body size to various populations. A higher fat mass is seen as healthier and more desirable in certain cultures. Healthcare providers should think about what “health" means to each person.
Given that major health choices, such as surgical procedures and weight reduction programs, are focused on BMI and weight, it is critical that all health providers look beyond BMI to ensure they are providing patient-centred recommendations.
As a measure of health, BMI analyses simply a person’s weight and height, rather than the individual. Age, gender, ethnicity, body composition, medical history, and other characteristics may all have an impact on a person’s weight and health.
Despite its numerous limitations, BMI is nevertheless used as the main evaluation tool in all healthcare settings because it is easy, cost-effective, and accessible.
However, there are alternatives to BMI that could be better indicators of a person’s health; each has its own set of benefits and drawbacks.
A larger waist circumference — one that is more than 35 inches (85 cm) in women or 40 inches (101.6 cm) in men — suggests more abdominal fat, which is linked to an increased risk of chronic disease.
It’s simple to measure since all you need is a measuring tape.
It does not consider different body shapes (for example, apple-shaped vs. pear-shaped) and structures (e.g., muscle and bone mass).
A high ratio (more than 0.80 in women or greater than 0.95 in men) shows increased fat deposits in the stomach and is associated with an increased risk of heart and chronic illness.
A low ratio (less than or equal to 0.80 in women and less than or equal to 0.95 in males) indicates more hip fat storage, which is linked to improved health.
It’s easier to measure since all you need is a measuring tape and a calculator.
It does not take into account varied body shapes (for example, apple-shaped vs. pear-shaped) and buildings (e.g., muscle and bone mass).
Body fat percentage
Body fat percentage refers to a person’s proportionate quantity of body fat.
It differentiates between fat mass and fat-free mass and is a more accurate estimate of a health risk than BMI.
Convenient assessment tools (like skinfold measurements, portable bioelectrical impedance tests, and at-home scales) have a significant error rate.
More precise technologies (such as dual-energy X-ray absorptiometry, underwater weighing, and BodPod) are costly and beyond of reach for many people.
Lab tests are a number of blood and vital sign assessments that might indicate the risk of chronic diseases (e.g., blood pressure, heart rate, cholesterol, blood glucose levels, inflammation).
These tests give a more thorough evaluation of a person’s metabolic health and do not depend just on body fat as a health indicator.
Typically, a single lab result is insufficient to diagnose or identify risk.
Regardless of the evaluation technique employed, healthcare providers should not depend just on one exam. A healthcare expert, for example, may examine a person’s BMI and waist circumference, and if a concern is raised, a blood test may be performed.
Each patient must be treated as an individual in order to discover what health means to them – physically, psychologically, emotionally, and spiritually.
Other body assessment measures, such as waist circumference, body fat percentage, and blood tests, may be used instead of BMI. Each, though, has its own set of pros and downsides.
The Bottom Line
Body mass index (BMI) is a highly disputed health assessment metric used to assess a person’s body fat and risk of disease.
According to research, when BMI rises over the “normal" range, the risk of chronic disease rises. A low BMI (below 18.5) is also associated with poor health outcomes.
However, BMI does not take into account other variables of health, such as age, gender, fat mass, muscle mass, race, genetics, and medical history. Furthermore, it has been proven that using it as the only predictor of health increases weight bias and health disparities.
Though BMI might be a good starting point, it should not be your primary indicator of health.