Nutrition advice is everywhere, but clarity is harder to find. Between headlines, trends, and conflicting opinions, it is not always clear what actually matters for long-term health.
That is why we have partnered with Dr. Joey Muñoz, PhD, to break down the science behind body composition, muscle, and longevity, starting with the foundations. In this three-part, evidence-based series, we explore:
- Why muscle plays a critical role in long-term health and aging
- How different types of body fat influence metabolism and inflammation
- Why the number on the scale does not tell the full story, and what to focus on instead
Each article is designed to help you better understand what is happening inside your body, so you can make more confident, informed decisions about your health.
Part 1 begins with the basics: what body composition really means, and why it matters more than weight alone. Keep reading to learn more!
Understanding Muscle’s Role in Longevity
When most people think about “health,” they picture the heart, the brain, or the lungs. But there’s another organ that plays a massive role in how long and how well you live: your muscle. Beyond strength and appearance, muscle functions as a true longevity organ, affecting everything from how your body processes nutrients to how it protects you as you age.
Muscle: the Longevity Organ
It’s easy to think of muscle as something only athletes or bodybuilders need, but science has made it clear: maintaining muscle is one of the strongest predictors of health and lifespan. Muscle tissue is active, constantly influencing metabolism, hormones, and immune function. Unlike fat, which stores energy, muscle uses it, making it one of the main drivers of your metabolic rate. The more muscle you have, the more efficiently your body handles the energy you consume.
As we age, we naturally lose muscle mass and strength, a process known as sarcopenia. This decline often starts quietly in your 30s and accelerates after 50. It’s one of the main reasons older adults experience slower metabolism, higher body fat, loss of balance, and increased frailty. But sarcopenia isn’t inevitable. It’s largely a result of inactivity and inadequate protein intake, not simply “getting old.” People who continue resistance training and eat enough protein can maintain muscle mass well into their 70s and beyond.
Muscle and Metabolic Health
Muscle isn’t just about movement; it’s also one of the body’s most powerful regulators of blood sugar. When you eat carbohydrates, your muscles act like a sponge, drawing glucose out of the bloodstream and storing it as glycogen for energy. This process improves insulin sensitivity, helping your body maintain stable blood sugar levels.
When muscle mass decreases, this buffering system weakens. Your body becomes less efficient at handling glucose, which can lead to insulin resistance and increase the risk of metabolic diseases like type 2 diabetes. That’s why two people with the same body weight can have completely different metabolic health profiles: one with more muscle and less fat will usually have better insulin control and energy stability, even if the scale shows the same number.
Building and maintaining muscle is one of the most effective long-term strategies for improving metabolic health. It’s like upgrading your body’s fuel system, allowing it to run cleaner, burn more efficiently, and stay balanced no matter what life throws at you.
Aging, Sarcopenia, and Longevity
Every decade after 30, you can lose up to 3–8% of your muscle mass if you don’t do anything to preserve it. That gradual decline doesn’t just change your physique, it affects how you move, recover, and even how your body responds to illness. Sarcopenia has been linked to a higher risk of falls, slower recovery from surgery, and greater vulnerability to infections. In other words, it’s not just about living longer, it’s about staying strong longer.
Strength training is essentially a longevity protocol. It tells your body, “We still need this tissue.” It activates growth signals, enhances mitochondrial function, and even improves brain health. Combined with proper nutrition, especially adequate protein intake, training becomes one of the most potent anti-aging interventions available. People who prioritize strength and movement as they age don’t just live more years; they live those years with more independence, energy, and confidence.
Protecting Against Injuries and Frailty
Muscle also acts as your body’s built-in armor. It stabilizes joints, supports posture, and absorbs impact during movement. When you have enough lean mass, you’re less likely to suffer falls, strains, or fractures. Even if an injury does occur, recovery is faster because strong muscles enhance circulation and tissue repair.
Think of muscle as your foundation. Without it, everything else becomes harder: walking up stairs, lifting groceries, getting out of bed, or simply keeping your balance. With it, life feels lighter. You move better, you recover faster, and your body stays functional longer. That’s what “aging well” really means—not avoiding years, but making those years count.
Putting It All Together
If fat is the storage system of the body, muscle is the engine. It drives movement, burns energy, stabilizes blood sugar, protects your joints, and keeps your body biologically young. Losing muscle doesn’t just mean losing strength; it means losing one of your most important allies for health and longevity.
So next time you train, don’t think of it as “just a workout.” You’re literally strengthening the organ that keeps you alive and thriving. Every rep, every set, every meal rich in protein is a message to your body: stay strong, stay capable, stay young.
Optimizing Your Protein Target
If you’re looking to build or maintain muscle, one of the most impactful changes you can make is increasing your daily protein intake beyond the standard guideline-based targets.
For most people, a protein intake in the range of 0.8–1.2 grams per pound of goal body weight (or 1.8–2.6 g/kg) is ideal for supporting muscle growth, strength, and healthy aging.
You can easily adjust your protein target inside the Cronometer app to match these evidence-based recommendations. Set your custom target in the More → Targets → Macros & Energy Targets section to align your tracking with your muscle-building goals. To learn more about setting your targets on Cronometer check out our blog here.
Coming Up Next in This Series
I hope you enjoyed part 1 of our 3 part series on body composition and health. Stay tuned for the next newsletter article for more evidence-based insights to help you live and perform at your best. We’ll be talking about fat, what role it plays in health, and its effects on chronic inflammation! Stay tuned.
Best, Dr. Joey Munoz
Nutrition Science Ph.D., Founder of Fit4Life Academy
