Understanding The Lean Body Mass

Lean body mass is calculated as the difference between total body weight and body fat weight, or more simply, the weight of everything except the fat.

By: Nina Teicholz, Published on: 2023-12-05, Last Updated: 03-08-24

Reviewed by: Huria Saleem

Table of Contents


When it comes to health, fitness, and body composition, the scale number doesn’t tell the whole story. Lean body mass (LBM) is an important metric that deserves more attention, especially among those looking to lose fat, gain muscle, and improve metabolic health.

So what exactly is lean body mass? It’s everything in your body except fat. This includes muscle, bone, ligaments, tendons, organs, and water weight. Essentially, any body weight that is not composed of fat makes up your lean mass. The higher your ratio of lean to fat mass, the more metabolically healthy you tend to be.

What is Lean Body Mass (LBM)?

Lean body mass (LBM) refers to the weight of your body minus all fat mass. It includes muscle, bone, bodily tissue, and all other fat-free mass in the body. Actually, LBM is everything that remains if you extract all the body fat. This metabolically active tissue consumes calories around the clock to sustain itself, contributing significantly to your total daily energy expenditure.

People often confuse lean mass with muscle mass. While muscle does make up an important portion of lean mass, it also includes organs, other tissues, and even bone. Anything that is not fat or water weight counts toward lean body mass. Determining and tracking LBM can provide useful health and fitness awareness.

Why is Lean Body Mass important?

There are several reasons why lean body mass is important:

1. Metabolism and Calorie Burning

Building lean body mass (LBM) can boost your metabolism and help you burn more calories, even at rest. This is because LBM is metabolically active tissue that requires energy for maintenance. As a result, even gaining a few pounds of muscle can increase your daily calorie burn by 50 or more calories.

2. Strength and Physical Function 

The more LBM you possess, the stronger and more physically capable you tend to be. More muscle and lower body fat facilitate improved strength for daily activities, athletic performance, injury flexibility, and keeping up energy levels. Preserving lean mass protects against age-related declines in strength and function.

3. Healthier Body Composition 

Maintaining a lower body fat percentage while building lean body mass is associated with a healthier body composition and a reduced risk of weight-related health problems such as diabetes and heart disease. Additionally, strong muscles and bones contribute to overall well-being and power as we age.

4. Body Recomposition 

Tracking LBM is a better way to assess changes in your body because it measures muscle, bone density, and organs, not just fat loss and water changes. This helps you see how well your fitness plan and lifestyle changes are working to improve your body composition.

Prioritizing LBM growth and maintenance is linked to better health, body function, metabolism, and body composition. Evaluating and boosting LBM is beneficial for most people in many ways.

Components of Lean Body Mass

Here are the key components that make up lean body mass (LBM) in the human body:

1. Organs

All bodily organs, including the brain, liver, kidneys, heart, lungs, pancreas, spleen, reproductive organs, thyroid, and adrenal glands, are metabolically active tissues that make up lean mass. Despite their small size, organs play a crucial role in human metabolism and physiology. Maintaining organ mass and function becomes increasingly important as we age.

2. Skin

The skin is the largest organ system in the human body, accounting for a significant portion of lean body mass. It is a dynamic, multifunctional tissue that performs crucial barrier functions. Adult skin alone weighs about 6 pounds (3 kg) and comprises roughly 5% of body mass. The skin's extracellular matrix proteins, cells, glands, and layers add to the total LBM.

3. Bones

The entire human skeleton, including teeth, makes up the body's structural framework while also interacting with fat storage and hormone regulation. Bone is metabolically active, dense connective tissue that requires energy for constant remodeling processes. Adult bone mineral content paired with marrow adds over 15% to total lean mass.

4. Body Water

Water makes up the largest part of lean body mass, ranging from 45 to 60 percent of total body weight in adults. It circulates through plasma, organs, muscles, and the digestive system, playing a vital role in temperature regulation and nutrient transport.

5. Muscle Mass

Muscles, organs, skin, and bones work together to form lean body mass. These tissues are all metabolically active, which means they burn calories even at rest. Tracking changes in lean body mass is important for people who are trying to lose weight or gain muscle.

How To Calculate Lean Body Mass?

There are a few common methods used to estimate total lean body mass (LBM). The most accurate laboratory assessments involve dual-energy x-ray absorptiometry (DEXA) and hydrostatic weighing. However, LBM can also be roughly calculated using mathematical formulas that factor in sex, height, weight, body fat percentage, or a combination of these variables.

Basic LBM calculation options include:

Subtract Body Fat Pounds from Total Weight

  • Body fat% x Weight in lbs = Fat mass lbs
  • Weight in lbs - Fat mass lbs = LBM

Use Lean Mass Formula for Men

  • LBM (lbs) = (1.10 x Weight in lbs) - 128 x (100/Weight in lbs)

Use Lean Mass Formula for Women

  • LBM (lbs) = (1.07 x Weight in lbs) - 148 x (100/Weight in lbs)

More complex formulas like the James, Brozek, and Hume equations incorporate additional measurements from skin folds or limb circumferences along with heights and weights.

What is The Average Lean Body Mass by Height and Weight?

General averages for LBM based on statistics correlate strongly with height and weight, as follows:

  • 5’8” tall, 160 lb male = roughly 145 lb LBM
  • 5’4” tall, 120 lb female = roughly 95 lbs LBM

However, averages vary widely by age, fitness level, bone density, and muscularity. Athletes often demonstrate elevated LBM.

Lean Body Mass Percentage

Typical LBM percentages of the total body weight span:


Ideal LBM Percentage





Elite Athletes

60–75% (Men), 50–65% (Women)

Elderly Adults

25–40% (Men), 20–35% (Women)


Boys: 30-45%, Girls: 25-40%

Good And Bad Lean Body Mass

Good LBM ranges correlate with:

  • Higher calorie burn and metabolism
  • Increased strength and mobility
  • Greater resilience against weight gain
  • Healthy body fat-to-lean mass ratio

Bad or low LBM represents:

  • Quicker loss of strength/function
  • Decreased metabolic rate
  • Higher risk of severe weight gain
  • Imbalanced body composition

How Does Lean Body Mass Affect Your Metabolism?

Lean tissue, unlike fat, is metabolically active, requiring consistent energy even at rest. This directly ties lean body mass to daily metabolic rate and calorie burning.

In basic terms, the more pounds or kilograms of lean mass on your body, the more calories you will burn just carrying out vital physiological processes because:

  • Organs need energy to function and maintain homeostasis
  • Muscle fibers continually rebuild, contract and facilitate movement
  • Bone undergoes remodeling and regeneration cycles
  • Water supports thermoregulation and hydration requires pumping fluids

Building lean muscle through resistance training can boost your metabolism and help you burn more calories, even at rest. Muscle protein synthesis, the process of building muscle tissue, burns a significant amount of calories during recovery and growth.

A higher proportion of lean body mass to fat mass helps keep your metabolism running faster. As we age, maintaining and supporting lean body mass becomes increasingly important to counteract the natural slowdown of metabolism and prevent unwanted fat storage, even if our diet and activity levels remain unchanged.

Factors Affecting Lean Body Mass

Here are key factors that affect lean body mass:

1. Genetics

While genetic factors like ethnicity and body type can influence overall lean body mass, lifestyle choices play a significant role in determining muscle growth, bone density, organ size, and other aspects of lean body composition.

2. Age

As we age, hormonal changes and reduced activity can lead to a gradual loss of muscle mass, bone mineral density, hydration, and organ weight over the years. Maintaining muscle mass through exercise and nutrition becomes increasingly important as we get older.

3. Sex

Adult males typically have 10–15% more lean body mass than females, even when considering height and frame size. This difference is due to variations in hormone levels, which influence muscle and bone growth.

4. Diet

Maintaining a balanced diet rich in protein, calcium, and vitamin D helps build and maintain lean muscle mass while supporting bone health. Staying hydrated also contributes to preserving lean body mass.

5. Hormones

Anabolic hormones like testosterone and growth hormones that stimulate tissue growth correlate with higher lean mass. Declining hormone levels with age contribute to losses of muscle and bone over time.

6. Exercise

Strength training stimulates muscle growth and bone density, preventing muscle loss that occurs with age. Even basic physical activity helps maintain muscle mass by applying mechanical stress to tissues.

What Can I Do to Improve Lean Body Mass?

Here are some effective tips for improving your lean body mass:

1. Start Resistance Training

Weightlifting and bodyweight exercises that progressively challenge your muscles are powerful stimuli for building muscle. Aim for 2-4 training days per week to prompt muscle protein synthesis. This directly increases lean mass.

2. Eat More Protein

Consuming enough protein—about 0.6–1 gram per pound of body weight daily—provides amino acids to facilitate new muscle growth when paired with training. A high protein intake preserves lean mass.

3. Achieve a Calorie Surplus

By consuming a high-quality diet with an excess of calories and engaging in challenging resistance training that stimulates muscle growth, you can effectively increase muscle mass over time.

4. Get Plenty of Rest

Muscles don’t actually grow during workouts. Complete rest between sessions enables exercised muscles to fully regenerate and become bigger and stronger. Prioritize sleep and avoid overtraining.

5. Stay Hydrated

To improve your overall lean body mass composition in the long term, you should focus on a combination of resistance training, a high-protein diet, gaining weight from quality calories, getting enough rest, and staying hydrated.

Association Between Protein Intake and Lean Body Mass

Eating enough protein is linked to building more muscle mass and maintaining a lean weight as you age. Studies have shown 3 main benefits:

  1. More Protein = Better Muscle Growth Consuming more protein after workouts helps feed muscles so they repair and grow bigger faster.
  2. More Muscle Gains from Training People eating high-protein foods while weight training typically gain 3–4 more pounds of muscle over 3 months compared to people eating less protein.
  3. Preventing Age-Related Muscle Loss Older adults need more protein as they age. Those who eat more protein lose less muscle and bone mass over time compared to seniors who don't get enough protein daily.

In easier terms, adequate protein intake, especially when combined with resistance exercise, is strongly associated with improved rates of muscle building, bigger muscle gains from lifting weights, and preventing the loss of muscle and lean tissues as you get older.

Final Words

In conclusion, understanding and optimizing lean body mass (LBM) is necessary for overall health, fitness, and performance. By increasing and maintaining LBM through regular resistance training, adequate protein intake, proper rest, a balanced diet, and professional guidance, you can enhance your metabolism, physical performance, bone health, and overall well-being. Hold a lifestyle that prioritizes LBM development and experiences the transformative power of a well-conditioned body.

Frequently Asked Questions

What 4 major things make up lean body mass?

Lean body mass represents the weight of your muscles, bones, ligaments, tendons, and internal organs.

What is a good lean body mass?

The range of lean body mass considered to be healthy is around 70%–90%, with women being towards the lower end of the range and men higher.

How much protein per lean body mass?

Most studies suggest that 0.7–1 gram per pound (1.6–2.2 grams per kg) of lean mass is sufficient.

Is lean body mass the same as muscle mass?

They're not the same. Lean body mass includes muscle mass, as well as bones and bodily fluid. Muscle mass is the size of your muscles.

What causes the loss of lean body mass?

The main symptom of the condition is muscle weakness. Sarcopenia is a type of muscle atrophy primarily caused by the natural aging process.

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