Does BMI Account for Muscle? Experts Explain Why It’s Not the Best Measure of Health

Body mass index (BMI) is a widely-used screening tool to estimate body fat using height and weight. It  categorizes people as “underweight,” “normal weight,” “overweight” and “obese” based on these measurements. Of course, these qualifiers have health implications. But the limitations of this metric have become a popular topic of conversation recently. One central question: does BMI account for muscle mass? 

In one viral TikTok video, Olympic rugby player Ilona Maher responds to a comment surmising that her BMI is 30 percent. It’s 29.3 percent to be exact, she confidently confirms before explaining that she’s been “considered overweight” since she was a child. 

The athlete, who led the United States to its first bronze Olympic medal in rugby sevens at the Paris games earlier this summer, went on to say that she had a conversation with her dietitian about the flaws of BMI specifically regarding athletes. 

At 5’10” and 200 pounds, Maher says she has an estimated 170 pounds of lean muscle mass on her body. 

“That BMI doesn’t really tell you what I can do,” she says. “It doesn’t tell you what I do on the field, it doesn’t tell you how fit I am, it’s just a couple numbers put together. It doesn’t tell you how much muscle I have or anything like that.” 

Does BMI account for muscle? 

The short answer is no, BMI does not discern fat from muscle mass. To calculate your BMI, you simply divide your weight by the square of your height. This is arguably the most important limitation, as BMI does not evaluate body composition. What does that mean? People with more lean muscle will likely have a higher BMI. 

“This is a problem for people like athletes with strong, muscular builds who may be categorized as overweight by BMI standards, despite having a low body fat percentage,” explains Chris Mohr, PhD, RD, fitness and nutrition advisor at Fortune Recommends Health. “Therefore, BMI provides a general health estimate but may not reflect true physical health, particularly for those with high muscle mass.” 

BMI overlooks the fact that muscle is denser than fat and typically takes up less space in the body, Mohr explains. Muscle also plays a key role in metabolism that BMI doesn’t consider: it burns calories at rest, increasing your metabolic rate. 

Why is that important? A high BMI reading puts you at a higher risk of everything from heart disease to high blood pressure to certain types of cancer. But that assumes your BMI is higher due to excess fat–not lean muscle mass. Your risk for certain health conditions may not actually be increased if you have lots of lean muscle mass that BMI doesn’t account for.

How to tell if your BMI reading is skewed 

“If you exercise a lot and have a muscular build, your BMI might be higher than normal, but you still look lean and fit,” explains Raj Dasgupta, MD, ABIM quadruple board-certified physician and medical reviewer for the National Council on Aging. 

“You can tell your BMI is off if you have a toned body, low fat and a healthy waist size, even if the number suggests you're overweight.” (A waist circumference of 35 inches or more increases your risk of heart disease and type 2 diabetes.)

This is especially true if you’re someone who lifts weights regularly or engages in resistance training, says Errol Clark, Certified CrossFit Trainer at Rocky Point Fitness. There’s a good chance your BMI might be misleading if it’s deemed higher than normal, but your waist-to-hip ratio is low, indicating less fat storage around your midsection, he adds. 

“Other key indicators, like your overall fitness level, energy and strength can also clue you in that BMI isn’t telling the whole story,” says Clark. 

Alternatives to BMI

Body roundness index (BRI) is one alternative to BMI. While it still doesn’t break down how much of your body is muscle vs. fat, it does include waist and hip circumference for a better overall picture of body composition. 

While there are a few measurements that may be more valuable for body composition insights than BMI, the gold standard tests that can give you exact percentages of fat, muscle, bone, water and more are typically hard to access. 

DXA, or Dual X-ray Absorptiometry, for example, uses x-ray beams to scan your body and precisely differentiate between bone mineral, lean mass and fat mass. With that being said, there aren’t many facilities that have the proper equipment to perform these tests. 

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This content is not a substitute for professional medical advice or diagnosis. Always consult your physician before pursuing any treatment plan.