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Lean body mass
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Lean body mass (LBM), sometimes conflated with fat-free mass, is a component of body composition. Fat-free mass (FFM) is calculated by subtracting body fat weight from total body weight: total body weight is lean plus fat. In equations:
- LBM = BW − BF
- Lean body mass equals body weight minus body fat
- LBM + BF = BW
- Lean body mass plus body fat equals body weight
LBM differs from FFM in that cellular membranes are included in LBM although this is only a small percent difference in the body's mass (up to 3% in men and 5% in women)[1]
This article may be confusing or unclear to readers. (August 2025) |
Overview
[edit]The percentage of total body mass that is lean is usually not quoted – it would typically be 60–90%. Instead, the body fat percentage, which is the complement, is computed, and is typically 10–40%. The lean body mass (LBM) has been described as an index superior to total body weight for prescribing proper levels of medications and for assessing metabolic disorders, as body fat is less relevant for metabolism. LBW is used by anesthesiologists to dose certain medications. For example, due to the concern of postoperative opioid-induced ventilatory depression in the obese patient, opioids are best based on lean body weight. The induction dose of propofol should also be based on LBW.[2]
Estimation
[edit]LBM is usually estimated using mathematical formulas. Several formulas exist, having different utility for different purposes. For example, the Boer formula is method of choice for LBM estimation to calculate the dose given in contrast CT in obese individuals with BMI between 35 and 40.[3]
A nomogram based on height, weight and arm circumference may be used.[4]
Boer
[edit]The Boer formula is:[3]
For men: LBM = (0.407 × W) + (0.267 × H) − 19.2
For women: LBM = (0.252 × W) + (0.473 × H) − 48.3
where W is body weight in kilograms and H is body height in centimeters.
Hume
[edit]The following formula by Hume may be used:[5]
For men: LBM = (0.32810 × W) + (0.33929 × H) − 29.5336
For women: LBM = (0.29569 × W) + (0.41813 × H) − 43.2933
where W is body weight in kilograms and H is body height in centimeters.
Actual measurement
[edit]Instead of mathematical estimation the actual value of LBM may be calculated using various technologies such as Dual-energy X-ray absorptiometry (DEXA).
See also
[edit]References
[edit]- ^ Yu, S; Visvanathan, T; Field, J; Ward, LC; Chapman, I; Adams, R; Wittert, G; Visvanathan, R (14 October 2013). "Lean body mass: the development and validation of prediction equations in healthy adults". BMC Pharmacology & Toxicology. 14 53. doi:10.1186/2050-6511-14-53. PMC 3833312. PMID 24499708.
LBM differs from FFM in that lipid in cellular membranes are included in LBM but this accounts for only a small fraction of total body weight (up to 3% in men and 5% in women)
- ^ Stoelting's Anesthesia and Co-Existing Disease, 6th Edition. Pages 329-330.
- ^ a b Caruso, Damiano; De Santis, Domenico; Rivosecchi, Flaminia; Zerunian, Marta; Panvini, Nicola; Montesano, Marta; Biondi, Tommaso; Bellini, Davide; Rengo, Marco; Laghi, Andrea (13 August 2018). "Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula". BioMed Research International. 2018 8521893. doi:10.1155/2018/8521893. ISSN 2314-6133. PMC 6110034. PMID 30186869.
- ^ Fuchs, RJ; Theis, CF; Lancaster, MC (1 April 1978). "A nomogram to predict lean body mass in men". The American Journal of Clinical Nutrition. 31 (4): 673–8. doi:10.1093/ajcn/31.4.673. PMID 637039.
- ^ Hume, R (Jul 1966). "Prediction of lean body mass from height and weight". Journal of Clinical Pathology. 19 (4): 389–91. doi:10.1136/jcp.19.4.389. PMC 473290. PMID 5929341.
Lean body mass
View on GrokipediaFundamentals
Definition and Terminology
Lean body mass (LBM) is defined as the total weight of the body minus the mass of adipose tissue, encompassing all non-fat components such as muscle, bone, organs, and water.[3] This represents the metabolically active portion of the body, excluding storage fat but potentially including minimal essential lipids.[9] In adults, LBM typically comprises 60-90% of total body weight, varying by age, sex, and fitness level, with higher proportions in leaner individuals.[10] The fundamental equation for LBM is: This calculation relies on accurate determination of fat mass through validated methods.[3] For example, for an individual weighing 78 kg with 19.5 kg of fat mass, LBM would be 78 kg - 19.5 kg = 58.5 kg. This formula assumes that LBM remains roughly constant during fat loss, provided there is minimal muscle loss, which can often be achieved through interventions such as adequate protein intake and resistance exercise.[11] Conversely, given lean body mass and body fat percentage, total body weight can be calculated using the rearranged formula: For example, a person with 106 kg of lean body mass and 10% body fat percentage weighs approximately 117.78 kg in total (106 kg / 0.90 ≈ 117.78 kg). In this case, fat mass is approximately 11.78 kg (10% of total weight), and lean body mass constitutes 106 kg (90% of total weight). LBM is often distinguished from fat-free mass (FFM), though the terms are sometimes used interchangeably in literature.[9] Specifically, LBM includes a small amount of essential lipids integral to cell membranes and other structures—approximately 2-3% of LBM, consistent across sexes—while FFM, as chemically defined, excludes extractable neutral fats but includes these essential structural lipids. Modern analyses confirm LBM and FFM have the same chemical composition, and FFM is preferred in scientific contexts to reduce ambiguity.[3][12] This subtle difference arises from the physiological versus strictly chemical perspectives in body composition analysis.[12] The concept of LBM originated in early 20th-century studies on body composition, particularly through work on body density and obesity assessment.[13] Captain Albert R. Behnke formalized the term in 1942, defining it as the body's weight excluding non-essential fat to better index physiological leanness beyond total body weight alone.[3] This evolved from underwater weighing techniques that differentiated fat from denser tissues.[9] LBM is typically expressed in kilograms for absolute measures or as a percentage of total body weight for relative comparisons across individuals.Components of Lean Body Mass
Lean body mass (LBM) consists of all non-adipose tissues in the body, encompassing skeletal muscle, bone, organs, connective tissues, body water, and minor biochemical elements such as non-fat cellular lipids. These components interrelate structurally and functionally, with water forming the largest proportion and influencing overall LBM stability through hydration status.[14] Skeletal muscle represents the dominant tissue in LBM, typically comprising 40-50% of its total mass in adults, with proportions reaching up to 50% in young males due to higher muscle development.[15][16] Bone mineral content accounts for approximately 15-20% of LBM, providing structural support and varying by density, while organs and connective tissues contribute 10-15%, including vital structures like the heart, liver, and tendons.[17] Body water constitutes 70-75% of LBM, distributed across all tissues and serving as a solvent for metabolic processes, with dehydration potentially altering LBM estimates by 1-2 kg.[18] Non-fat cellular lipids, essential structural fats in cell membranes and organelles, make up a small fraction (about 2-3%) of LBM, distinguishing it from adipose tissue.[3] Biochemically, LBM includes proteins such as myofibrillar proteins in skeletal muscle that enable contraction, minerals like calcium and phosphorus concentrated in bone for mineralization, and glycogen stores primarily in muscle and liver cells for energy reserve, typically amounting to 300-500 grams in adults.[19][20] These elements maintain homeostasis, with proteins forming 15-20% of dry LBM weight and minerals about 6-7%.[21] Proportional breakdowns shift across demographics and life stages; for instance, muscle mass declines with age, dropping 3-8% per decade after age 30, reducing its share of LBM from peak levels in youth.[22] Males generally exhibit higher bone mineral proportions due to greater density (about 10-15% more than females), contributing to overall LBM differences.[17] During pregnancy, LBM increases by 2-5 kg, driven by expansions in uterine tissue, placenta, and extracellular fluids, enhancing maternal physiological capacity.[23]Biological Significance
Metabolic and Physiological Roles
Lean body mass (LBM), encompassing fat-free tissues such as muscle, organs, and bones, serves as the primary driver of resting energy expenditure (REE), explaining 70-80% of the inter-individual variance in REE.[24] This metabolic contribution arises because LBM components, particularly metabolically active tissues like skeletal muscle and viscera, consume the majority of energy at rest to maintain cellular functions and homeostasis.[25] A common method for estimating REE based on LBM is the Katch-McArdle formula:This equation, derived from empirical data on lean tissue metabolism, applies uniformly to males and females and underscores LBM's role in basal energy needs without gender-specific adjustments.[26] Beyond energy expenditure, LBM plays essential physiological roles in supporting basal metabolism, thermogenesis, and metabolic regulation. It facilitates basal metabolism by sustaining vital processes like organ function and cellular repair, which account for 60-70% of total daily energy use.[27] LBM also contributes to thermogenesis, including non-shivering mechanisms in skeletal muscle that generate heat to maintain core temperature during environmental stress.[28] Furthermore, higher LBM enhances insulin sensitivity, promoting efficient glucose uptake and reducing the risk of metabolic disorders, as muscle tissue acts as a key site for insulin-mediated glucose disposal.[29] Specific components of LBM fulfill targeted physiological functions. Skeletal muscle, comprising the largest portion of LBM, drives protein turnover and amino acid metabolism, serving as the body's primary reservoir for amino acids and regulating whole-body protein balance through synthesis and breakdown processes.[30] Bones, another critical LBM element, maintain mineral homeostasis by storing over 99% of the body's calcium and phosphate, releasing or absorbing these ions as needed to stabilize blood levels and support neuromuscular and enzymatic activities.[31] Research highlights the protective effects of LBM against mortality. Meta-analyses from the 2010s, including those examining sarcopenia (low LBM), consistently link higher LBM to reduced all-cause mortality risk, with low lean mass associated with a 20-30% increased hazard compared to higher levels, independent of age and comorbidities.[32][33]
