When It Comes to Health, Muscle Mass Matters

The Doctor Weighs In
5 min readJan 13, 2019

By: Suzette Pereira Ph.D

Muscle mass plays a huge role in predicting health outcomes and yet is rarely assessed in clinical practice.

Photo source: iStock Photos

Most doctors use BMI to assess health, which is overlooking a major vital sign — muscle mass.

For decades, our society has been using a person’s body mass index, commonly known as BMI, to determine a person’s health. Yet for many, this simple math equation — dividing a person’s weight by the square of their height — offers an incomplete picture of health because it doesn’t take important health factors like muscle mass into account. In fact, nearly 1 in 5 people have a misleading BMI, according to the CDC’s National Health and Nutrition Examination Survey.

BMI fails to account for differences in muscle mass

BMI first became popular in the 1970s as a way to assess the prevalence of obesity across large, diverse populations for tracking long term trends. It has since then become the go-to way to assess people’s health. Yet, BMI ignores major individual health factors like age, chronic conditions, and physical activity level.

Additionally, BMI is just based on body weight and does not differentiate between fat mass and muscle mass (also known as body composition). Having more muscle mass is associated with better health and greater longevity. Because BMI doesn’t account for someone’s muscle mass, it overlooks this important health indicator entirely.

Since muscle weighs more than fat, it’s common for people to get wrongly characterized as either healthy or unhealthy based on their BMI. For example, athletes whose muscular physique misleads the scale could end up being erroneously classified as overweight. Conversely, others who have a normal BMI with very little muscle could appear in the “healthy” range, but actually, have low muscle mass putting their long-term health at risk.

In both cases, body composition is being ignored by BMI. For the athlete, it’s a simple flaw of the measurement. For others, research has found that ignoring a person’s body composition, especially their muscle mass, can lead to confusion about a person’s health status, and can be a matter of life or death in some cases.

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