Muscle Health Part 2

Is it Time to
Move On from BMI?

Measuring your body mass index (BMI) might not give an accurate picture of your overall health. A better measurement might be lean body mass (LBM), which measures muscle mass–a predictor of your health–within the whole composition of your body.

Illustrations by Guilherme Henrique

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Since the 1980s, people have used two simple measurements to create a picture of their overall health: their height and weight. When you divide your weight in kilograms by your height in meters, and then by that height number again, you get your body mass index, commonly called your BMI. Doctors use this number to tell you if you’re underweight, normal weight, overweight, or obese. General guidelines say that people with a normal BMI are healthy; those in any other category are most likely not healthy.

If that seems too simple, that’s because it is–deceptively so, says Suzette Pereira, an Abbott researcher who studies the role of muscles in health and disease. She explains that weight alone does not give a complete picture of overall health, because it overlooks “the intricacies of body composition”–that is, the ratios of muscle, fat, bone, and fluid in your body. Regardless, the guidelines became so widely accepted that in 2015 the U.S. Equal Employment Opportunity Commission proposed a regulation that would allow businesses to penalize workers up to 30 percent of health insurance costs if their BMIs did not fall into a certain range.

After the EEOC proposal, a group of psychologists at the University of California, Los Angeles, set out to determine if BMI was as telling as accepted. The team measured subjects’ BMIs as well as metabolism and blood pressure. The results challenged the quality of BMI as an indicator of overall health: Nearly half of the people whose BMIs labeled them as overweight or obese were in fact healthy, while more than a third of people with normal BMIs were deemed unhealthy.

BMI also misses other information that is important to understanding our overall health.

Because it is based on weight, it doesn’t differentiate between fat and muscle. That means it tells us nothing about body composition–and that’s a problem, because body composition can tell us how much muscle mass we have, and the ratio of muscle to fat in our bodies. Knowing how much muscle we have, and how strong that muscle is, can tell us whether we are at risk of falling, slower recovery from injury, and progression of chronic illness, to name a few. Lean body mass offers that missing insight by clarifying how much muscle mass we have.

Having sufficient muscle mass and strength is important on a day-to-day basis. What’s more, it’s a huge factor in being able to bounce back from injury and illness. Thankfully, muscle loss and related functional decline is gaining awareness, and emerging as a prominent consideration for older adults. Sarcopenia, which is the clinical name for muscle loss with associated loss of strength or function in aging adults, has even recently been assigned an international classification for disease by the Centers for Disease Control and Prevention, upping its visibility as a medical issue.

BMI Vs. LBM

With the same body type, they must be equally healthy. Or are they?

BMI Vs. LBM

Even for two people with the same BMI measurement, body composition can look wildly different.

An overweight person may be considered unhealthy based on BMI, but actually have a higher muscle-to-fat ratio than a person with a normal or low BMI. Likewise, a person with a low BMI may have more muscle mass than a person with a normal BMI, thus setting them up to be healthier in old age–but if their doctors focus solely on BMI, they’ll miss this.

BMI vs. LBM

With the same body type, they must be equally healthy. Or are they?

Even for two people with the same BMI measurement, muscle health can look wildly different.

As muscle loss progresses, you might be walking more slowly, and find it harder to keep your balance or stand up from a chair.

"If [a person with low BMI] has the right amount of muscle and they're functioning well, they can walk fast, they can lift things, they have good grip strength, then they actually are not at risk of sarcopenia," Pereira explains. Even a person with a high BMI who appears to improve their health by losing weight might actually be doing more harm than good, if the weight loss is due to muscle loss rather than fat loss.

To understand overall health, Pereira says, it’s more important to concentrate on a less-commonly known measurement: lean body mass (LBM).

LBM specifically measures non-fat mass in your body. Maintaining enough muscle mass, through muscle-friendly food choices and exercise, can actually help prevent muscle loss, malnutrition, and heart disease, as well as enhance recovery from injury. One number, it turns out, does say a lot–it’s just that BMI is no longer the one number that most people need to focus on.

Track Muscle Health

How do you calculate your LBM?

To calculate your LBM, you first need to know your body fat percentage. You can find this by weighing yourself on a body fat scale. Then subtract your body fat percentage from your overall weight. For example, if you weigh 140 pounds and have 20 percent body fat percentage (roughly 28 pounds), you would have about 112 pounds of lean body mass.

Track Muscle Health

Know the signs of muscle loss, and stay aware of your body.

  1. When done by a doctor, a skin caliper can measure your body fat percentage and help you determine your LBM.
  2. A bioelectric impedance analysis (BIA) scale can measure out the components of your body composition–including LBM (muscle), body fat, bone density, and fluid.
  3. Be aware of the strength of your grip: If it’s weakening, it could signal muscle loss.
  4. Notice whether you have any difficulty walking up stairs or inclines.
  5. Check if you're walking at your usual pace, or if you've slowed down.
Track Muscle Health

How do you calculate your LBM?

To calculate your LBM, you first need to know your body fat percentage. You can find this by weighing yourself on a body fat scale. Then subtract your body fat percentage from your overall weight. For example, if you weigh 140 pounds and have 20 percent body fat percentage (roughly 28 pounds), you would have about 112 pounds of lean body mass.

Know the signs of muscle loss, and stay aware of your body.

  1. When done by a doctor, a skin caliper can measure your body fat percentage and help you determine your LBM.
  2. A bioelectric impedance analysis (BIA) scale can measure out the components of your body composition–including LBM (muscle), body fat, bone density, and fluid.
  3. Be aware of the strength of your grip: if it’s weakening, it could signal muscle loss.
  4. Notice whether you have any difficulty walking up stairs or inclines.
  5. Check if you're walking at your usual pace, or if you've slowed down.

The most important step in maintaining your muscle (and by extension, your overall) health is even simpler than calculating your LBM, adds Pereira: Listen to your body. “If you know the signs of muscle loss, the biggest thing is you feel it before you can actually measure it.” LBM is certainly more precise than BMI–but it’s still a number, a measurement. It’s up to you to make sense of the number, by regularly asking yourself whether you’ve noticed changes in your day-to-day routine.

“[We are] working on more tools to measure lean body mass, but that comes with education too,” says Pereira. “Once you know that you have low [LBM], then you know what you need to do to intervene. It’s never too late.”