What Peter Attia’s “Outlive” Teaches Us About Muscle, Longevity, and the Role of DEXA Scans

In his bestselling book Outlive, Dr. Peter Attia explores the science of longevity and the habits that help people not just live longer but stay physically capable well into their later years. One of his key messages is simple: maintaining and building muscle is one of the most powerful levers we have for extending both lifespan and “healthspan.”
At Dexa Health, we see that same principle play out every day. DEXA scans give us one of the most precise ways to measure muscle mass and track the progress of anyone looking to optimize their long-term health. Here’s how Attia’s ideas connect directly to the data we capture in a DEXA scan.

Muscle Mass Is a Predictor of Longevity

Dr. Attia emphasizes that muscle mass and strength are two of the strongest predictors of healthy aging. As we get older, we naturally lose muscle through a process called sarcopenia. This decline affects balance, metabolism, and overall resilience. Attia refers to this as a critical factor in “Medicine 3.0,” the proactive approach to preventing decline before it starts.
Research supports his view. People with lower skeletal muscle mass are at significantly higher risk of falls, frailty, hospitalization, and even all-cause mortality. Conversely, those who maintain strong muscle tissue tend to live longer and more capable lives. That’s why understanding where your muscle mass stands today is so important, and why DEXA scans are one of the best ways to do it.

RSMI: A Key Indicator of Muscle Health

The Relative Skeletal Muscle Index (RSMI), derived from a DEXA scan, provides a simple yet powerful measure of muscle health. It’s calculated by taking your appendicular lean mass (the sum of lean tissue in your arms and legs) and dividing it by your height squared. The result is a number that reflects how much muscle you carry relative to your body size.
Why is this so valuable? Because raw lean mass alone doesn’t tell the full story. A taller person will naturally have more lean mass, so RSMI adjusts for height and gives a fair comparison across individuals. This lets us determine whether someone’s muscle level is considered low, average, or above average for their body frame.
Attia’s message aligns perfectly with this idea. Being above average in muscle mass relative to your size is protective for long-term health. In fact, people in the top quartile for muscle mass and strength have lower risks of disease and mortality. RSMI helps us see where you stand on that spectrum and track whether you’re moving in the right direction.

Why DEXA Scans Matter More Than Ever

A DEXA scan is more than just a body fat test. It’s a window into your muscle distribution, bone health, and visceral fat, all of which influence longevity and performance. While scales and bioimpedance devices can estimate body composition, they often miss the nuance that DEXA provides.
Dr. Attia’s philosophy centers on data-driven prevention, and that’s exactly where DEXA fits in. By quantifying your muscle mass, fat mass, and bone health over time, you can make informed decisions about your training, nutrition, and recovery. You can also spot early warning signs of muscle decline long before they become visible or symptomatic.
For anyone serious about extending healthspan, DEXA scans provide the kind of objective feedback that aligns perfectly with Attia’s approach. They allow you to measure, adjust, and optimize, which forms the foundation of any long-term health strategy.

What to Aim For

Research and experts like Dr. Peter Attia suggest aiming for roughly the 75th percentile or higher, which usually means an RSMI of about 8.7–9.0 kg/m² for men and 6.3–6.5 kg/m² for women. Maintaining muscle mass in this range is linked to better strength, mobility, and long-term health as you age.

The Bottom Line

Peter Attia’s Outlive reframes longevity around proactive measurement and strength, not waiting for decline but preventing it. DEXA scans make that philosophy practical. They quantify the very metrics Attia considers vital: muscle mass, body composition, and bone health.
In short, what gets measured gets improved. A DEXA scan gives you the numbers that matter most for your long-term vitality, helping you train, eat, and live with intention. It’s not just about knowing your body composition; it’s about building the foundation for a longer, stronger life.

References and Further Reading

Attia, Peter. Outlive: The Science and Art of Longevity. Harmony Books, 2023. Learn more about Dr. Attia’s work at peterattiamd.com/outlive.
Baumgartner RN et al. “Epidemiology of sarcopenia among the elderly.” American Journal of Epidemiology, 1998.
Gould H et al. “The relative skeletal muscle index and mortality risk in adults.” Clinical Nutrition, 2014.
Kim J et al. Reference values for appendicular skeletal muscle mass and prevalence of sarcopenia in the US population based on NHANES 1999–2004. The Journals of Gerontology: Series A. 2015;70(10):1320–1326.