The human body is made up of two types of tissues: lean mass and fat mass. The fat mass is constituted by the body fat, anhydrous, and in the reference man it constitutes about 15% of the body weight. The lean mass instead represents the mass obtained by subtracting the value of the fat mass from the body weight and represents about 85% of the weight, and is anatomically constituted by skeletal muscles (about 40%) (muscle mass), non-skeletal muscles, lean tissues and organs (about 35%) and skeleton (about 10%).
Skeletal muscle, which is the main component of lean mass, is a tissue to which great attention has been paid in the world of body composition because, if stimulated correctly, it can greatly increase its volume and metabolic functions.
Mainly the muscle has three macro functions:
- provides support, movement and strength
- stores water and glycogen and is a potential energy reserve
- produces anti-inflammatory cytokines (in this case called myokines)
When the intake of nutrients and in particular of proteins with the diet is insufficient and physical activity is inadequate, the body uses muscle as a source of energy, resulting in a loss of muscle mass and therefore lean mass. Loss of muscle mass can have negative health consequences and affect many aspects of life, including mobility and autonomy, the ability to carry out activities of daily living and quality of life.
Muscle loss is a physiological process as we age, but certain conditions such as chronic illness, prolonged immobilization, malnutrition, bed rest and post-hospitalization can accelerate this natural process and lead to a decline. muscle strength and / or function resulting in a condition called sarcopenia.
It is important to know, however, that these changes in body composition can occur regardless of age and body weight and also that more and more studies associate a reduction in muscle mass as a predictor of increased morbidity and mortality in the population.
In particular, the study "Implications of Low Muscle Mass across the Continuum of Care: A Narrative Review" published in September 2018 in the journal Annals of Medicine, provides an overview of the influence of low muscle mass on the health status of patients in hospital, outpatient and long-term care settings. From this review it emerges that reduced muscle mass is associated with greater surgical and post-operative complications, longer length of hospital stay, more limited physical performance, lower quality of life and lower survival. Therefore, the authors believe that the potential clinical benefits deriving from the prevention and reversal of this condition in patients affect not only the health status of patients but also the use of resources and therefore health costs.
Body mass measurement parameters such as weight and body mass index (BMI) have long been regarded as practical and sensitive tools for determining health conditions and predicting related risks. For years, BMI has been relied on to assess patients' health but this, if not properly interpreted, can be misleading as it does not distinguish between different body components. In fact, although they are very useful, these measurements do not represent the variability of an individual in body composition that is, lean tissue versus adipose tissue rather than body water and it is also good to keep in mind that body composition can be variable between individuals of the same size. thus confusing the association between body weight and health.
For this reason, especially in hospital settings or in general in situations of compromised health conditions, clinically more valid instruments are needed to measure body composition both for screening and for routine checks.
- Prado CM, Purcell SA, Alish C, et al. Implications of low muscle mass across the continuum of care: a narrative review. Ann Med. 2018; 50 (8): 675-693. Available at https://doi.org/10.1080/07853890.2018.1511918