Most of us have heard the term body mass index (BMI) before. (After all, it is a standard health assessment tool that’s often used in healthcare facilities.) And for decades, BMI has used body size to measure people’s overall health. However, it’s recently faced some backlash for oversimplifying the meaning of health.
So, is BMI outdated? Many health experts tend to think so. In today’s article, we’ll illuminate everything you need to know about BMI, its history, and why it’s not (spoiler alert) an accurate picture of health.
So, What Is BMI?
The BMI scale was developed in 1832 by a Belgian mathematician named Lambert Adolphe Jacques Quetelet. Essentially, he designed it to quickly estimate the degree of obesity in a population, as the government needed to know how to allocate health resources. But because it only provides a snapshot of a population’s overall health, Quetelet said himself that it would be an inaccurate way of assessing individual health.
BMI is calculated by dividing a person’s weight by their height. There are different formulas depending on the various measurement systems:
- weight (kg) / height (m2)
- (weight (lbs) / height (in2)) x 703
Once BMI is calculated, practitioners will evaluate where it falls on the BMI scale. The higher the BMI, the more likely a person will be classified as being overweight or obese.
The Problems with BMI
BMI Fails to Consider Other Aspects of Health
BMI determines whether a person is a ‘normal’ weight without considering factors like sex, age, genetics, lifestyle, or medical history. Therefore, relying solely on BMI causes many people to overlook other important health indicators. (Think: cholesterol levels, blood sugar, heart rate, blood pressure, inflammation levels, etc.)
In addition, BMI uses the same calculation for men and women. However, the different sexes have different body compositions, and men have more muscle mass and less fat mass than women. Similarly, our body fat increases and our muscle mass decreases as we age. And numerous studies have shown that a higher BMI (23.0 to 29.9) in older adults protects against early death and disease.
BMI Assumes All Weight is Equal
Compared to fat, muscle is denser and occupies less space. However, BMI doesn’t differentiate between fat and muscle. For that reason, it’s not uncommon for someone who’s incredibly lean (aka has a high muscle mass) to be misclassified as ‘overweight.’ Therefore, it’s important to consider a person’s muscle, fat, and bone mass (in addition to their body weight) when evaluating health.
BMI Fails to Consider Fat Distribution
Though a higher BMI is linked to poor health outcomes, the distribution of fat throughout the body also plays a role. For instance, those who store fat in their stomach area have a greater risk of chronic disease than those who store fat in their hips and lower body.
BMI Might Not Be Relevant for All Populations
Despite its popularity, BMI does not accurately reflect the health of specific racial and ethnic populations. In fact, research shows that people of Asian descent with lower BMIs have an increased risk of chronic diseases than their white counterparts.
BMI Might Cause Weight Bias
Historically, some medical professionals have based their recommendations solely on a person’s BMI. And as you can probably imagine, this can lead to weight bias and poor quality healthcare. People with higher BMIs report that their doctors overly emphasize their body weight – even if their appointment is for an unrelated concern. And oftentimes, this causes serious medical issues to be overlooked as weight-related problems.
Better Indicators Of Healthy Weight
While it’s true that BMI offers a snapshot of a person’s overall health, it doesn’t consider factors like sex, race, genetics, bone density, fat, and muscle mass. Therefore, there are better indicators of healthy weight:
Essentially, a larger waist circumference—one greater than 35 inches in women or 40 inches in men indicates greater body fat in the abdominal area. And that increases one’s risk for chronic diseases like type 2 diabetes, high blood pressure, and coronary artery disease. However, it fails to differentiate between different body types.
Under this weight indicator, a higher waist-to-hip ratio (greater than 0.80 in women or greater than 0.95 in men) suggests higher fat stores in the stomach area. And of course, that is linked to a greater risk of heart and chronic disease. On the other hand, a lower ratio suggests higher hip fat storage, which is generally associated with better health.
Body Fat Percentage
Body fat percentage measures the relative amount of body fat a person has. And because it distinguishes between fat mass and fat-free mass, it’s a more accurate health assessment than BMI.
Lab tests measure various blood and vital signs that indicate chronic disease risk. Generally, they test cholesterol levels, blood pressure, heart rate, blood glucose levels, and inflammation. And unlike BMI, it provides a more detailed view of a person’s metabolic health. (However, it’s worth noting that a single lab value does not sufficiently diagnose or indicate risk.)
So, Is BMI Outdated?
By now, we hope that you have your answer. While medical professionals have long used BMI to measure health, it certainly has its flaws. And because BMI fails to consider muscle mass, fat distribution, age, gender, or genetics, we don’t recommend basing your health status on BMI alone. Instead, use your waist circumference, waist-to-hip ratio, body fat percentage, and lab test results to formulate a comprehensive picture of their health—which should all be measured by your medical doctor.