Β-Hydroxy β-methylbutyric acid
β-Hydroxy β-methylbutyric acid (HMB) is a naturally occurring metabolite of the essential amino acid leucine. It plays a crucial role in protein metabolism, muscle recovery, and anabolic processes. HMB is often used as a dietary supplement to support muscle growth, reduce muscle breakdown, and enhance exercise performance.
Biosynthesis and Metabolism[edit]
HMB is produced in the human body through the metabolism of leucine:
- Leucine is first converted into α-ketoisocaproate (KIC) via branched-chain aminotransferase (BCAT).
- KIC is then metabolized by ketoisocaproate dioxygenase (KICD) in the liver to form HMB.
- Approximately 5% of dietary leucine is converted into HMB.
HMB undergoes further metabolism:
- It is converted into β-hydroxy β-methylbutyryl-CoA (HMB-CoA).
- HMB-CoA enters the cholesterol synthesis pathway, supporting cell membrane repair.
- A portion of HMB is also metabolized into β-hydroxy β-methylglutaryl-CoA (HMG-CoA), a precursor to cholesterol.
Physiological Functions[edit]
HMB is believed to have several physiological roles, including:
- Reducing muscle protein breakdown (anti-catabolic effect).
- Enhancing muscle protein synthesis via the mTOR signaling pathway.
- Improving recovery from resistance training and high-intensity exercise.
- Supporting immune function and reducing muscle loss in individuals with cachexia or sarcopenia.
Dietary Sources[edit]
HMB is naturally found in small amounts in:
- Animal-based foods such as milk, cheese, and eggs.
- Plant-based sources such as alfalfa.
- Muscle tissue metabolism following dietary leucine intake.
Use as a Dietary Supplement[edit]
HMB is available as a nutritional supplement in two main forms:
- HMB-Free Acid (HMB-FA) – Rapidly absorbed and bioavailable.
- HMB-Calcium Salt (HMB-Ca) – More stable, commonly used in commercial products.
It is often used for:
- Sports performance enhancement – Reducing exercise-induced muscle damage.
- Elderly health – Preventing muscle wasting and promoting functional mobility.
- Clinical applications – Used in conditions like cachexia, cancer-related muscle loss, and HIV/AIDS-associated wasting.
Clinical Research[edit]
Studies on HMB have shown:
- Muscle Mass and Strength – HMB supplementation combined with resistance training improves muscle strength and lean body mass.
- Endurance Performance – May reduce exercise-induced muscle damage and enhance recovery.
- Aging and Sarcopenia – Beneficial in preventing age-related muscle loss.
- Medical Conditions – Used in patients with chronic diseases to preserve muscle mass.
Safety and Side Effects[edit]
HMB is generally considered safe when used at recommended doses (3g/day). Potential side effects include:
- Gastrointestinal discomfort in some individuals.
- No reported toxicity at commonly used doses.
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ISSN HMB statement Fig 2
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Butyric acid carbons 2
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Beta-Hydroxy beta-methylbutyric acid 2
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HMB synthesis historical
