HMB: an Ally for Recovering Muscle Mass

With advancing age, after long hospital stays, or in illnesses associated with muscle wasting, people may experience a loss of muscle mass known as sarcopenia. Oral supplementation with nutrients such as β-hydroxy-β-methylbutyrate (HMB) can help preserve muscle strength and function.

Loss of Muscle Mass

Sarcopenia is characterised by a loss of muscle mass and strength, a common condition in many situations. It can have serious physiological consequences—from loss of independence and reduced mobility, to physical disability. Sarcopenia can have various causes. It may be due to the natural ageing process; it may be linked to inadequate nutrition or malabsorption; or it may be caused by chronic diseases associated with muscle wasting (such as some types of cancer, acquired immunodeficiency syndrome, chronic obstructive pulmonary disease, kidney disease or liver disease) ⁽¹⁾. For example, in patients with liver cirrhosis, sarcopenia affects up to 70% of individuals ⁽²⁾. Finally, it may result from long periods of inactivity and immobility, which are typical of prolonged post-trauma hospitalisation. In this regard, it is estimated that around 65% of older patients experience a reduction in physical function after hospitalisation. Because a low-protein nutritional status is one of the main factors in the onset and progression of sarcopenia, supplementing the diet with HMB-based nutritional products may be helpful to counteract muscle loss and preserve muscle protein synthesis—supporting improvements in strength and physical function.

HMB: what it is and what it does

HMB is a substance produced from the metabolism of leucine, an essential branched-chain amino acid. HMB is present in small amounts in some foods, such as avocados, citrus fruits and cauliflower. Leucine regulates and controls protein synthesis in muscle cells, and HMB is a key metabolite in this regulation. HMB has been shown to:
modulate muscle protein breakdown by inhibiting the ubiquitin–proteasome proteolytic pathway
regulate protein synthesis through the mTOR pathway
stabilise cell membranes by modulating the enzyme that regulates cholesterol synthesis (HMG-CoA reductase) (1) Despite these important functions, only around 5% of leucine is converted into HMB (3). Based on daily dietary leucine intake, it is estimated that the body of a 70 kg adult man produces around 200–400 mg of HMB per day. These are very small amounts, which is why HMB supplementation may be useful in preserving or rebuilding muscle mass in populations at risk of sarcopenia.

Scientific studies on HMB

Several studies have shown the benefits of oral HMB supplementation—alone or combined with other amino acids and an exercise protocol—in improving muscle strength, preventing loss of tone and promoting the maintenance of muscle mass in adults and older people. A clinical study published in Clinical Nutrition showed that nutritional intervention with HMB (3 grams/day) preserves muscle mass in people forced into long periods of inactivity (for example during hospital admission) (4). In diseases such as liver cirrhosis, often associated with malnutrition, frailty and sarcopenia, supplementation with 3 grams/day of HMB has been shown to be effective in improving physical performance and muscle mass ⁽⁵⁾. A 2019 review analysing randomised clinical studies involving more than 203 people with sarcopenia or frailty concluded that, following HMB supplementation in older people with sarcopenia, lean mass increased and muscle strength and function were preserved ⁽⁶⁾.