What’s More Important BMI or Body Fat Percentage?
by Melinda Burris
This article discusses the pros and cons of BMI, body fat percentage calculations, and medical waist measurement as simple ways for you to gauge your weight and fat percentage. Remember, all of these methods are indicators, not a comprehensive overview of your health. The findings below will likely surprise you!
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Why BMI is So Frequently Used
Body mass index or BMI became the standard recognized by the health community for measuring weight class and risk of obesity since the National Institute of Health adopted the use of BMI to ascertain risk for obesity and obesity-related health conditions in 1985.1 BMI is also a simple standard that calculates an individual’s weight class as underweight, normal, overweight, or obese based on comparing their weight to their height.2 It’s generally agreed by experts that the medical community uses the BMI because it’s easy, inexpensive, and considered to be generally accurate. However, as The Wall Street Journal notes, the BMI can “[misclassify] patients because it does not distinguish fat from muscle.”3 This is a cause for concern when seeking to get a true picture of whether your body fat and weight can be categorized as healthy.
Claire Edgemon, a senior registered dietitian at Baylor College of Medicine, agrees, noting, “Both body fat percentage and BMI are important to monitor. They give you a good starting point, but you don’t want to use BMI alone to make a health diagnosis or define body fat.”2 Why? Because BMI only considers weight and height, not other important factors like a breakdown of the individual’s muscle, bone, and fat mass.2
Why BMI Alone Isn’t Enough
Dr. Holly F. Lofton, an internist specializing in obesity medicine and the director of NYU’s Langone’s Weight Management Program, confirms, “You can have two people with the same BMI, but one has 50 percent body fat and the other has 30 percent body fat.”3 For obvious reasons, this is problematic, to say the least, when you are seeking to determine whether a person is obese.
According to Dr. Lofton, health insurance companies also rely on BMI levels and will only approve certain treatments for patients if they fit within a certain percentage based on the index.2 Another easy and low-cost way to evaluate for obesity is the medical waist measurement. It is just as cost-effective and carries less risk of wrongly categorizing a person with a muscular physique as overweight or even obese.
How to Do a Medical Waist Measurement
To do a medical waist measurement, simply measure the waist just above the hip bones. For males, a waist medical measurement of more than 40 inches is considered to be in the obese range. For females, a measurement of more than 35 inches is an indicator of obesity.3
Edgemon warns against relying solely on BMI, stating, “If BMI is used alone, it could be misleading about an individual’s health status.”2 It is important to bear in mind that a person with a BMI that is considered to be in the normal range may still suffer from other health conditions and may be at risk for others. Edgemon asserts it is important to look beyond the BMI and the limited factors it takes into consideration and investigate how the metabolic process is performing as well as other health measurements including blood pressure and glucose and cholesterol levels.2
Using BMI and Body Fat Percentage Together
Edgemon recommends calculating your BMI and your body fat percentage and then considering the results together to determine if your weight is at a healthy level.2 If you find you need to lose a few pounds, the rules haven’t changed. Concentrate on eating a healthy, low-fat diet with fewer calories and increasing your exercise level to bring your weight back to a healthy level.
Dr. Lofton makes an important point when she states, “There is a healthy range for body fat percentage, but there are differences to consider, like age or gender. A healthy body fat range is 25-31% for women and 18-24% for men; this doesn’t consider age or athletic status.”3 So, although things like BMI and body fat percentage are easy to calculate online, and the medical waist measurement is simple to do, there are many factors to consider when determining overall good health.
Dr. Lofton does warn that although BMI and waist circumference are helpful measurements to gauge obesity, they “are not diagnostic tools for disease risks.”3 She recommends that if you calculate your BMI online and find that it is high, you should see a medical care professional to seek advice about what this means, the general state of your health, and any potential risks you may face.3
The Genesis of BMI
Ancel Keys, a researcher working in the 1970s to find the most efficient method of measuring body fat, did a research study based on results from more than 7,500 participants. Keys tried three methods including water displacement, skin calipers, and body mass index. The latter was determined to be the most accurate and cost-efficient means of measuring body fat. Keys’ study was acutely flawed because all of the test subjects were men and the majority of those men were white.1 Because of this, the results of Keys’ research fail to reflect the differences in the sexes or the differences in races.
Carolyn Roberts cites one scientific study with thousands of participants that showed “African American women with the same BMIs as white women were found to have better health markers in areas like blood pressure and cholesterol, suggesting that BMI can define black people as ‘unhealthy’ when in reality they aren’t.”1 Proving the BMI is flawed when measuring fat and obesity risks in populations other than a group of predominately white men, Roberts goes on to cite another research study, noting one “that tracked the health of more than 78,000 women in the US [and] found that Asian Americans were at a higher risk of developing obesity-related illnesses at lower BMIs than their white counterparts.”2 These are just two of many evidence-based studies that demonstrate the BMI has issues.
Roberts goes further, making the argument that the body fat percentage has proven to be a reliable indicator of serious conditions including but not limited to diabetes, high blood pressure, and increased risk of mortality in individuals whose BMI or weight would classify them as being healthy.1 There are still many questions to be asked and answered about BMI, body fat percentage, and how best to judge when weight is putting someone’s health or even their life at risk.
Follow the advice of medical professionals, use the BMI, the body fat percentage, and/or the medical waist measurement as an approximation when you feel your weight may be an issue. Then, promptly see your medical care provider for a full physical examination so you have a clear picture of your current state of health and what you can do to improve it!
References:
- Roberts, C. (16 July 2020). Body Mass Index vs. Body Fat Percentage: Only One of Them Actually Matters.
- Barnes, T. (4 January 2024). Body fat percentage vs. BMI – Which is important?
- The Wall Street Journal. (13 August 2021). The Wall Street Journal: Why Doctors Rely on BMI to Measure Obesity.
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