Updated: Aug 10
HMB, also known as beta-Hydroxy beta-methylbutyric acid, is a molecule produced by your body when the amino acid Leucine, one of the protein building blocks, is broken down.
HMB is metabolised from Leucine by liver enzymes at a rate of roughly 5%, therefore supplementing with BCAAs or Leucine alone won't help you raise HMB levels adequately. (1)
What Does It Do
HMB functions via several different pathways, one of which is as a precursor to a rate-limiting enzyme in cholesterol production.
HMG-coenzyme A reductase is an enzyme that converts HMG to coenzyme A. (2)
This is significant because when we exercise, we damage the muscle cell membranes, which are made up in part of lipids and cholesterol, which the body needs to repair.
All of this must occur before contractile tissue protein synthesis, thereby implying that dietary lipids and cholesterol might operate as a rate limiting factor for muscle development. (4)
HMB seems to only have a favourable impact when it comes to healing muscle cell membrane damage caused by new exercises, which it does via activating three key proteolysis pathways.
Calcium activated calpain (CAC)
The UB pathways are often observed to be active in new trainees, persons recovering from lengthy periods of zero gravity exposure (7, 8), exercise-induced catabolism (9), and other conditions that cause muscle atrophy or immobility.
This is important to remember since trainees who supplement with HMB for long periods of time have reduced UB activation with each bout of repetitive exercise. (10)
Lean Body Mass
Though this seems to be perplexing at first glance, I believe it is to be predicted given what we currently know. HMB is known to act by repairing damaged muscle cell membranes, enabling normal muscle protein synthesis to proceed.
When a fresh stimulus is introduced, the damage is usually worse.
If the body is exposed to a new stressor that it isn't adapted to, HMB supplementation will result in higher muscle protein synthesis, but if it adapts to the stimulation, less damage occurs, resulting in the same amount of muscle protein synthesis as it would otherwise.
HMB does not drive synthesis beyond a typical range; rather, it compensates for what would have happened otherwise.
There have been studies that have demonstrated advantage for highly trained athletes, which fits into the conclusion from the aspect of recuperation.
Overtraining, or reduced muscle protein synthesis from excessively injured muscle cells, occurs when muscles are repeatedly stressed without enough rest. (21)
Supplementation might help athletes achieve higher levels of continuous training.
Strength & Endurance
The greater recovery of athletes who push their bodies to the limit will explain for the strength and endurance improvements they experience, just as it will for new trainees who show increases above and beyond what their placebo group is seeing.
The improvement reported in the trained individuals might be due to compensating for overtraining-induced reductions in muscle protein synthesis.
If you are a mediocre gym goer, supplementing with HMB will not result in significant strength and endurance increases unless you put in a lot of work.
A small reduction in total fat mass has been seen in a few of the studies previously mentioned; this may be explained simply by the well-known processes of total metabolic rate.
Your body will need more calories to maintain its size as you gain muscle mass.
HMB has no fat oxidation properties of its own, however it does have a minor secondary impact.
Through 0g, 1.5g, and 3g, a dose-dependent impact was seen, with 3 grams being the most effective.
According to a more recent study, 6g of HMB does not provide any advantage above the normal amount of 3g, but it does provide a dosage scale of 38 mg/kg for effective dosing. (27)
HMB has a half-life of around 2.5 hours and reaches baseline levels after 9 hours. (28)
At stated doses the International Society of Sports Nutrition recommends HMB to be generally safe. (6)
But as always, ask your doctor if you have any concerns before starting a supplementation regime.
It seems that in order for this supplement to be of much benefit, we must go above and beyond our usual exercise routine.
It may be beneficial to highly trained people who are undergoing a demanding training regimen that necessitates prolonged recovery time or persons who are experiencing new muscular stresses.
HMB becomes far less appealing to people who use a constant progressive overload type of training, where our bodies have adapted to the stimulus and are engaged in regular muscle protein synthesis that is unaffected by HMB.
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This evidence based analysis of what HMB does and how it works features 28 references, listed below.
1. Tessari P, Nissen SL, Miles JM, Haymond MW. Inverse relationship of leucine flux and oxidation to free fatty acid availability in vivo. J Clin Invest. (1986, Feb) ✔
2. Wilson GJ, Wilson JM, Manninen AH. Effects of beta-hydroxy-beta-methylbutyrate (HMB) on exercise performance and body composition across varying levels of age, sex, and training experience: A review. Nutr Metab (Lond). (2008, Jan 3) ✔
4. Jówko E, Ostaszewski P, Jank M, Sacharuk J, Zieniewicz A, Wilczak J, Nissen S. Creatine and beta-hydroxy-beta-methylbutyrate (HMB) additively increase lean body mass and muscle strength during a weight-training program. Nutrition. (2001, Jul-Aug) (Clinical Trial) ✔
6. International Society of Sports Nutrition Position Stand: Beta-hydroxy-beta-methylbutyrate (HMB). Journal of the International Society of Sports Nutrition. (February 2013)
11. Asadi A, Arazi H, Suzuki K. Effects of β-Hydroxy-β-methylbutyrate-free Acid Supplementation on Strength, Power and Hormonal Adaptations Following Resistance Training. Nutrients. (2017, Dec 2) ✔
12. Lowery RP, Joy JM, Rathmacher JA, Baier SM, Fuller JC Jr, Shelley MC 2nd, Jäger R, Purpura M, Wilson SM, Wilson JM. Interaction of Beta-Hydroxy-Beta-Methylbutyrate Free Acid and Adenosine Triphosphate on Muscle Mass, Strength, and Power in Resistance Trained Individuals. J Strength Cond Res. (2016, Jul) (Randomised Controlled Trial) ✔
13. Holeček M. Beta-hydroxy-beta-methylbutyrate supplementation and skeletal muscle in healthy and muscle-wasting conditions. J Cachexia Sarcopenia Muscle. (2017, Aug) (Review) ✔
14. Cruz-Jentoft AJ. Beta-Hydroxy-Beta-Methyl Butyrate (HMB): From Experimental Data to Clinical Evidence in Sarcopenia. Curr Protein Pept Sci. (2018) (Review) ✔
15. Asadi A, Arazi H, Suzuki K. Effects of β-Hydroxy-β-methylbutyrate-free Acid Supplementation on Strength, Power and Hormonal Adaptations Following Resistance Training. Nutrients. (2017, Dec 2) ✔
16. Tritto AC, Bueno S, Rodrigues RMP, Gualano B, Roschel H, Artioli GG. Negligible Effects of β-Hydroxy-β-Methylbutyrate Free Acid and Calcium Salt on Strength and Hypertrophic Responses to Resistance Training: A Randomized, Placebo-Controlled Study. Int J Sport Nutr Exerc Metab. (2019, Sep 1) (Randomised Controlled Trial) ✔
17. Teixeira FJ, Matias CN, Monteiro CP, Valamatos MJ, Reis JF, Morton RW, Alves F, Sardinha LB, Phillips SM. Leucine metabolites do not attenuate training-induced inflammation in young resistance trained men. J Sports Sci. (2019, Sep) (Randomised Controlled Trial) ✔
18. Jakubowski JS, Nunes EA, Teixeira FJ, Vescio V, Morton RW, Banfield L, Phillips SM. Supplementation with the Leucine Metabolite β-hydroxy-β-methylbutyrate (HMB) does not Improve Resistance Exercise-Induced Changes in Body Composition or Strength in Young Subjects: A Systematic Review and Meta-Analysis. Nutrients. (2020, May 23) (Meta-Analysis) ✔
19. Thomson JS, Watson PE, Rowlands DS. Effects of nine weeks of beta-hydroxy-beta- methylbutyrate supplementation on strength and body composition in resistance trained men. J Strength Cond Res. (2009, May) (Randomised Controlled Trial) ✔
20. Kreider RB, Ferreira M, Wilson M, Almada AL. Effects of calcium beta-hydroxy-beta-methylbutyrate (HMB) supplementation during resistance-training on markers of catabolism, body composition and strength. Int J Sports Med. (1999, Nov) (Clinical Trial) ✔
21. High-Intensity Resistance Training with Insufficient Recovery Time Between Bouts Induce Atrophy and Alterations in Myosin Heavy Chain Content in Rat Skeletal Muscle. Muscle Biology. (28 June, 2011)
✔ Citations with a tick indicate the information is from a trusted source.
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