Why BMI is Not a True Indicator of Healthy Weight, and What to Use Instead

By Dr Luke McPherson (TCM)

Acupuncture, Crows Nest

Body Mass Index (BMI) has been the standard tool used to assess whether someone falls within a healthy weight range for decades. However, as more research emerges, it's becoming clear that BMI is not always the most accurate measure of health. While it’s easy to calculate and categorise individuals into broad categories—underweight, normal weight, overweight, and obese—it doesn’t take into account several critical factors that affect a person’s health. Let’s explore why BMI may not be the best indicator of healthy weight and what alternatives might provide a more accurate picture.

What is BMI?

Body Mass Index (BMI)  is calculated by dividing a person's weight in kilograms by their height in meters squared. The resulting number is compared to a scale to determine if they are underweight (BMI under 18.5), normal weight (18.5–24.9), overweight (25–29.9), or obese (30 and above).

Why BMI is NOT a True Indicator of Health

1.     Lack of Differentiation Between Muscle and Fat

BMI does not distinguish between muscle mass and fat. A person with a high level of muscle, such as an athlete or bodybuilder, may have a high BMI, which categorises them as overweight or even obese, despite having very low body fat and excellent cardiovascular health (Prentice & Jebb, 2001). Similarly, someone with low muscle mass but high body fat might fall into the "normal" range while still being at risk for metabolic disorders (Shah & Braverman, 2012).

2.     Doesn't Account for Fat Distribution

Research shows that where body fat is stored matters. Visceral fat, which is stored around the abdominal organs, is more dangerous than subcutaneous fat stored under the skin (Després, 2012). Two people with the same BMI could have very different health outcomes depending on where their fat is distributed, something BMI cannot account for (Zhang et al., 2008).

3.     Ignores Age, Gender, and Ethnicity

BMI does not account for age-related changes in muscle and fat composition, gender differences in body fat distribution, or ethnic variations in body composition. For instance, older adults might naturally have less muscle mass, making BMI less reflective of their health status (Heo et al., 2013). Some ethnic groups may have higher risks for conditions like diabetes at a lower BMI compared to others (Huxley et al., 2010).

4.     No Insight into Metabolic HealthA person with a normal BMI might still suffer from conditions like high cholesterol, high blood pressure, or insulin resistance. These “metabolically unhealthy normal-weight” individuals may face the same health risks as someone with a higher BMI, even though their weight appears to fall within a “healthy” range (Wildman et al., 2008).

What Should Be Used Instead?

Given BMI’s limitations, other metrics can provide a clearer picture of overall health:

1.     Waist-to-Hip Ratio (WHR)

The waist-to-hip ratio takes fat distribution into account by measuring the circumference of the waist compared to the hips. This gives insight into visceral fat, the type most strongly linked to cardiovascular disease. A higher WHR indicates a higher risk of health problems (Snijder et al., 2006).

2.     Body Fat Percentage

Unlike BMI, which lumps all weight together, body fat percentage specifically measures the proportion of fat compared to lean mass (muscles, bones, etc.). Body fat percentage can be measured with tools like skinfold callipers, bioelectrical impedance, or more advanced methods like DEXA scans, providing a more precise understanding of body composition (Wells & Fewtrell, 2006).

3.     Waist Circumference

Measuring your waist circumference alone can help assess the risk of metabolic disease. Research suggests that waist circumference correlates better with risks of conditions like diabetes and heart disease than BMI (Janssen et al., 2004). A waist circumference of more than 35 inches for women or 40 inches for men is often a red flag for potential health problems (Klein et al., 2007).

4.     Body Composition and Muscle Mass

Lean muscle mass plays an important role in overall health, affecting metabolism, insulin sensitivity, and strength. Focusing on muscle mass through regular strength training, rather than just reducing weight, can help improve long-term health outcomes (Donnelly et al., 2009). Tools like bioimpedance scales or DEXA scans can help assess muscle mass in relation to fat.

5.     Blood Markers and Metabolic Health

Health isn’t just about body composition—it’s also about what’s happening inside the body. Blood markers like cholesterol levels, fasting blood glucose, and blood pressure provide a window into metabolic health. These measurements can be early indicators of cardiovascular disease, diabetes, and other health risks, regardless of someone’s BMI (Stern et al., 2005).

The Importance of a Holistic Approach

Health is not a one-size-fits-all concept. A person’s weight is just one aspect of their overall well-being. When assessing health, it’s essential to take a holistic view, considering diet, physical activity, mental well-being, sleep quality, and other lifestyle factors. A number on a scale or a BMI category can’t capture the complexity of human health.

Final Word…

While BMI may still serve as a simple tool for population-wide assessments, it falls short of accurately reflecting individual health. Health professionals should consider other indicators like body fat percentage, waist-to-hip ratio, and blood markers when evaluating a person’s well-being. By focusing on these more precise and personalised metrics, we can better understand what a healthy weight looks like for each individual and guide them toward better long-term health outcomes.

Ultimately, the goal is not just a “normal” BMI, but a body and lifestyle that supports overall health and longevity.

All content, including but not limited to text, images, and ideas, presented in this blog are the intellectual property of the author, Dr Luke McPherson(TCM), and are protected by copyright law. Unauthorised use, reproduction, or distribution of this material without explicit permission from the author is strictly prohibited.

References

1.     Després, J. P. (2012). Body fat distribution and risk of cardiovascular disease: An update. Circulation, 126(10), 1301-1313. https://doi.org/10.1161/CIRCULATIONAHA.111.067264

2.     Donnelly, J. E., Blair, S. N., Jakicic, J. M., Manore, M. M., Rankin, J. W., & Smith, B. K. (2009). Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults. Medicine & Science in Sports & Exercise, 41(2), 459-471.

3.     Heo, M., Faith, M. S., Pietrobelli, A., & Heymsfield, S. B. (2012). Percentage of body fat cutoffs by sex, age, and ethnicity in the US adult population from NHANES 1999-2004. American Journal of Clinical Nutrition, 95(3), 594-602. https://doi.org/10.3945/ajcn.112.038611

4.     Huxley, R., Mendis, S., Zheleznyakov, E., Reddy, S., & Chan, J. (2010). Body mass index, waist circumference and waist ratio as predictors of cardiovascular risk—a review of the literature. European Journal of Clinical Nutrition, 64(1), 16-22. https://doi.org/10.1038/ejcn.2009.68

5.     Janssen, I., Katzmarzyk, P. T., & Ross, R. (2004). Waist circumference and not body mass index explains obesity-related health risk. American Journal of Clinical Nutrition, 79(3), 379-384. https://doi.org/10.1093/ajcn/79.3.379

6.     Klein, S., Allison, D. B., Heymsfield, S. B., Kelley, D. E., Leibel, R. L., Nonas, C., & Kahn, R. (2007). Waist circumference and cardiometabolic risk: A consensus statement from shaping America's health: Association for Weight Management and Obesity Prevention; NAASO, The Obesity Society; The American Society for Nutrition; and The American Diabetes Association. Obesity, 15(5), 1061-1067. https://doi.org/10.1038/oby.2007.632

7.     Prentice, A. M., & Jebb, S. A. (2001). Beyond body mass index. Obesity Reviews, 2(3), 141-147. https://doi.org/10.1046/j.1467-789x.2001.00031.x

8.     Shah, N. R., & Braverman, E. R. (2012). Measuring adiposity in patients: The utility of body mass index (BMI), percent body fat, and leptin. PLoS One, 7(4), e33308. https://doi.org/10.1371/journal.pone.0033308

9.     Snijder, M. B., van Dam, R. M., Visser, M., & Seidell, J. C. (2006). What aspects of body fat are particularly hazardous and how do we measure them? International Journal of Epidemiology, 35(1), 83-92. https://doi.org/10.1093/ije/dyi253

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