What is HMB?

Hydroxymethylbutyrate (HMB) is an active metabolite of the essential amino acid leucine. HMB is found in very small amounts in foods such as avocado, citrus fruit, cauliflower, and catfish.¹ HMB is made from leucine in the muscle and liver cells but only 5% of the leucine is converted to HMB, yielding very small amounts (0.2-0.4 grams in a 70 kg person) on a daily basis.

How does surgery alter muscle function?
The surgical stress response results in whole-body catabolism (breakdown of complex molecules to smaller ones). This is seen principally as the wasting of muscle, releasing amino acids to allow the synthesis of proteins known as acute phase reactants and production of glucose needed as an energy source.² In addition, perioperative fasting can worsen the surgical stress response, weaken gut function, and amplify protein losses. In patients with critical illness who may be also confined to bed rest, a vicious cycle is present with bed rest promoting muscle breakdown and the resultant muscle wasting and weakness preventing much needed ambulation and physical activity. It has been reported that patients in the acute care setting can lose about 2% of their muscle mass per day but with longer hospital stays, they can lose as much as 50% muscle mass.³ Loss of muscle mass has significant consequences, including muscle weakness, fatigue, risk of pulmonary complications (e.g. longer need for a ventilator, pneumonia), and prolonged hospitalization as a consequence of a slower recovery.

How does HMB work?

The effects of HMB resulting in an improvement of physical performance, stamina, or recovery are related to the inhibition of protein break-down, increased protein synthesis, stimulation of growth hormone, increase of muscle stem cells, and decreased cell death.⁴  

Does HMB supplementation alter outcomes?

HMB enhances recovery following exercise training and has been shown to increase lean body mass and functionality in the elderly.⁵ In a study evaluating the effect of HMB (3 grams/day) versus placebo in healthy older adults placed on 10 days of complete bed rest, lean body mass was preserved in patients treated with HMB, in contrast to placebo patients, who lost 2 kilograms of body weight.⁶ Similarly, in patients undergoing total knee replacement, muscle strength was preserved with HMB supplementation⁷ and in patients with a hip fracture, HMB accelerated wound healing, decreased the period of immobility, and increased muscle strength.⁸ HMB as part of protein supplementation also resulted in improved nutritional status, muscle strength, and 50% lower mortality at 90-days after-discharge in older malnourished hospitalized patients.⁹

What is the suggested dose of HMB?

The commonly recommended dose of HMB is up to 3 grams per day. However, this amount is difficult to obtain from usual diet because of the low transformation rate of leucine to HMB (see above) and therefore, supplementation is needed. Chronic consumption of HMB appears to be safe in both the young and the elderly and HMB appears to be most effective when taken for at least 2 weeks prior to training.⁵

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2. Gillis C, Wischmeyer PE. Pre-operative nutrition and the elective surgical patient: why, how and what? Anaesthesia. 2019;74 Suppl 1:27-35.
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4. Kaczka P, Michalczyk MM, Jastrzab R, Gawelczyk M, Kubicka K. Mechanism of Action and the Effect of Beta-Hydroxy-Beta-Methylbutyrate (HMB) Supplementation on Different Types of Physical Performance – A Systematic Review. J Hum Kinet. 2019;68:211-222.
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7. Nishizaki K, Ikegami H, Tanaka Y, Imai R, Matsumura H. Effects of supplementation with a combination of beta-hydroxy-beta-methyl butyrate, L-arginine, and L-glutamine on postoperative recovery of quadriceps muscle strength after total knee arthroplasty. Asia Pac J Clin Nutr. 2015;24(3):412-420.
8. Ekinci O, Yanik S, Terzioglu Bebitoglu B, Yilmaz Akyuz E, Dokuyucu A, Erdem S. Effect of Calcium beta-Hydroxy-beta-Methylbutyrate (CaHMB), Vitamin D, and Protein Supplementation on Postoperative Immobilization in Malnourished Older Adult Patients With Hip Fracture: A Randomized Controlled Study. Nutr Clin Pract. 2016;31(6):829-835.
9. Deutz NE, Matheson EM, Matarese LE, et al. Readmission and mortality in malnourished, older, hospitalized adults treated with a specialized oral nutritional supplement: A randomized clinical trial. Clin Nutr. 2016;35(1):18-26.