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So, is BMI outdated?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.
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
While research does confirm that a low (below 18.5) and high (above 30) BMI is associated with increased health risks, the measurement has numerous flaws:
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. BMI does not measure visceral fat, which is the fat stored around vital organs and is a significant risk factor for chronic diseases like cardiovascular disease and type 2 diabetes.
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 can also be misleading for older adults as they tend to lose muscle mass and bone density, which can result in a lower BMI despite having higher fat mass and associated health risks.
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.
BMI Doesn’t Consider Gender Differences
Men and women have different body compositions, with women generally having higher body fat percentages than men. BMI does not distinguish between these differences, leading to potential misclassification.
BMI Doesn’t Define Health Status and Overall Health
BMI is a single number that does not consider other critical factors affecting an individual’s health status, such as medical history, lifestyle, blood glucose levels, and cholesterol levels. It oversimplifies the complex nature of overall health.
BMI Doesn’t Consider Bone Density
Individuals with higher bone density, such as younger adults and athletes, might have a higher BMI that does not accurately reflect their fat mass or health risks.
BMI Doesn’t Indicate Chronic Disease Risk
Using BMI alone to gauge the risk of chronic diseases can be misleading. It does not account for factors like physical activity levels, dietary habits, and genetic predispositions that significantly impact health.
BMI May Contribute to Eating Disorders and Psychological Impact
Emphasizing BMI can contribute to body image issues and eating disorders, as individuals strive to meet certain weight categories without considering their overall health and body composition.
BMI Screening Tool’s Limitations
While BMI is useful for large groups of people and epidemiological studies, its use in individual health assessments is limited. Tools like bioelectrical impedance and dual-energy X-ray absorptiometry provide more detailed insights into body composition and health risks.
BMI Doesn’t Consider General Health and Individual Health
A person’s body weight and BMI should be considered alongside other measures of general health and individual health to provide a comprehensive assessment of their well-being and potential health risks.
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:
Waist Circumference
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.
Waist-to-Hip Ratio
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 Testing
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.)
Dexa Scans and Other Body Composition Assessments
DEXA (Dual-Energy X-ray Absorptiometry) scans and other body composition assessments provide detailed insights into an individual’s body composition, far surpassing the limitations of BMI. DEXA scans measure bone density, fat mass, and lean body mass, offering a comprehensive analysis of body composition and identifying areas of fat distribution, such as visceral fat around vital organs, which is a significant risk factor for chronic diseases.
Other advanced methods like bioelectrical impedance analysis (BIA) and magnetic resonance imaging (MRI) also measure body fat percentage, muscle mass, and overall body composition. These assessments help health professionals and individuals understand the nuanced relationship between body composition and health, allowing for more accurate health evaluations and personalized interventions.
Do Doctors Still Use BMI?
While BMI on its own is not an accurate measurement of health, doctors use BMI (Body Mass Index) because it is a quick, simple, and cost-effective tool for initial screening of weight categories that can indicate potential health risks. Here are several reasons why BMI remains widely used in clinical settings:
Ease of Use
BMI is straightforward to calculate using just height and weight measurements, making it easy to apply in various healthcare settings without requiring specialized equipment.
Initial Screening
As a preliminary screening tool, BMI can help identify individuals who may be at risk of weight-related health conditions, prompting further investigation and more detailed assessments.
Correlation with Health Risks
While not perfect, BMI is generally correlated with various health risks, such as cardiovascular disease, diabetes, and certain cancers, particularly at the extremes of the BMI spectrum (very high or very low BMI).
Guidelines and Protocols
Many medical guidelines and protocols from institutions like the National Institutes of Health (NIH) and the World Health Organization (WHO) include BMI as part of their criteria for diagnosing and managing obesity and related conditions.
Conclusion: 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 your health—which should all be measured by your medical doctor.
Here are some tips for healthy, simple ways to lose weight.
