What Is Lean Body Mass?
Lean Body Mass (LBM) is the weight of everything in your body except fat: muscles, bones, organs, water, and connective tissue. It is sometimes used interchangeably with Fat-Free Mass (FFM), though technically LBM includes a small amount of essential fat. LBM is a critical metric for setting protein targets, calculating drug dosages, and understanding body composition changes.
Why LBM Matters
LBM is the metabolically active portion of your body. Higher LBM correlates with higher BMR (you burn more calories at rest), better insulin sensitivity, stronger bones, and better functional outcomes in aging. Preserving LBM during caloric restriction is a primary goal of evidence-based fat loss protocols — which is why high protein intake and resistance training are essential during any diet.
The Boer Formula
The Boer formula estimates LBM from height and weight: for men, LBM = (0.407 × kg) + (0.267 × cm) − 19.2; for women, LBM = (0.252 × kg) + (0.473 × cm) − 48.3. It is one of the most validated LBM estimation formulas for general populations, though DEXA scan remains the gold standard.
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Content reviewed for accuracy using guidelines and research from the WHO, CDC, NIH, and peer-reviewed academic journals.
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Frequently Asked Questions
What is a healthy lean body mass percentage?
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There is no universal ideal LBM percentage as it varies with sex, age, and athletic status. Generally, athletic men might have 80–90% LBM (10–20% body fat) and athletic women 75–85% LBM (15–25% body fat). Total body weight, lean mass, and body fat percentage must all be considered together.
Why does my lean body mass number seem high?
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Lean body mass includes everything that is not fat: muscle, bone, organs, blood, connective tissue, and water. Water alone constitutes approximately 60–65% of total body weight and is included in lean body mass. A 75kg person with 15% body fat has approximately 63.75kg of lean body mass — which sounds high but is accurate when you account for the full composition of non-fat tissue.
How can I increase my lean body mass?
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Progressive resistance training is the primary method — compound movements (squat, deadlift, bench press, row) performed with consistent overload over months and years. Adequate protein (1.6–2.0g/kg) provides the amino acids needed for muscle protein synthesis. Sufficient sleep (7–9 hours) allows recovery and growth hormone secretion. These three factors — training, protein, sleep — account for the majority of lean mass development.
How do I increase lean body mass?
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Increasing LBM requires resistance training combined with adequate protein intake (1.6–2.4g/kg body weight) and a slight caloric surplus for maximum gains. Sleep quality, stress management, and progressive overload in training are also critical factors.
What is the difference between lean body mass and muscle mass?
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Lean body mass includes all non-fat tissue: muscles, bones, organs, water, and connective tissue. Muscle mass refers specifically to skeletal muscle tissue. LBM is always larger than muscle mass and is the value estimated by most body composition tools without DEXA or MRI scanning.