supplements

HMB - Hydroxy methyl butyrate

Generality

Hydroxy-methyl-Butyrate, also known as HMB, is a metabolic product synthesized by the body from leucine.

Endogenous synthesis

In the cellular environment, a part of this essential amino acid (leucine) with important anticatabolic functions undergoes a transamination reaction; the enzyme that catalyzes this reaction is called BCAT (specific transaminase for branched amino acids).

The resulting product is leucine ketoacid, called α-ketoisocaproate (KIC), to which the aforementioned anticatabolic properties of the amino acid precursor (leucine) have traditionally been ascribed.

Most of the KIC is then converted into isovaleryl-CoA, while a share of around 5% is metabolised to Beta-hydroxy Beta-methylbutyrate (HMB); the enzyme that catalyzes this reaction is called α-ketoisocaproate dioxygenase.

Ultimately, about 60 grams of leucine is required to synthesize three grams of HMB, which is not the case in common practice.

It is estimated that the body of a 70 kg adult man produces 200 to 400 mg of HMB per day, obviously also depending on the dietary intake of leucine.

HMB in Foods and Supplements

Hydroxy methyl butyrate was discovered in pig milk; small quantities can also be found in other foods, such as grapefruit, alfalfa and catfish.

Given its normal presence in food, HMB has been marketed as a patent-protected supplement for some years now.

In accordance with the results of some studies, supplementation with HMB would perform a valuable ergogenic effect, thanks to its anabolic, lipolytic and anti-catabolic properties with DOMS reduction.

Indications

Why is HMB used? What is it for?

Anti-catabolic and immunomodulatory properties have been ascribed to HMB for several years now.

Despite its anti-catabolic efficacy has been described in some critical conditions - such as sarcopenia of adulthood, oncologic cachexia or extensive trauma - the anticatabolic and anabolic effect on the healthy individual is still uncertain.

For this reason, the much-publicized capacity of HMB to increase muscle mass in healthy and fit individuals is still unclear.

The aura of mystery surrounding HMB is probably related to the presence of contradictory studies and to a mechanism of action that is not yet completely clear, which would see the involvement of particularly complex muscular metabolic pathways.

Property and Effectiveness

What benefits has HMB shown during the studies?

As mentioned, the scientific literature is somewhat debated on the real utility of the HMB in sports.

While HMB would seem to save muscle proteolysis induced by intense exercise, on the other hand there would not be an overall increase in muscle mass in healthy and training subjects (as opposed to what was observed on sarcopenic and defected patients).

For this reason the anabolic, anti-catabolic and immunomodulatory activity of HMB would seem to be closely related to factors such as sex, age, physical condition, muscular state and state of health.

In the health field, some studies have revealed hypocholesterolemic properties (against the LDL fraction) and antihypertensive of HMB; still others would suggest a possible positive effect on the immune system and wound healing, while for the aforementioned stimulus on protein synthesis HMB could be of potential help in cachectic states.

In this regard, we report an interesting and complete review of 2008, which examines all the main research conducted on HMB in recent years: Effects of beta-hydroxy-beta-methylbutyrate (HMB) on exercise performance and body composition across varying levels of age, sex, and training experience: A review - Gabriel J Wilson Jacob M Wilson Anssi H Manninen (freely available at this address).

Doses and method of use

How to use the HMB

Regarding the methods of intake, it is advisable to fractionate the daily intake into three single doses of one gram each or 12.5 mg per kg of body weight.

All this to compensate for the short plasma half-life of HMB, quantifiable in two and a half hours (with return to baseline levels within nine hours of intake).

Dosages higher than 3 grams per day do not seem to have significant additive effects.

HMB is generally sold in capsules, to be swallowed with water or other beverages.

Given its ergogenic properties, it would be interesting to evaluate the additive effects of a simultaneous association between HMB and supplements with similar characteristics, such as arginine, glutamine and BCAA.

Always on the basis of these considerations, the best moments to take HMB are breakfast, the protein snack that precedes night rest and the one that follows training.

Side effects

At the moment no noteworthy side effects are known following the use of HMB.

This safety was also confirmed by numerous other experimental studies conducted on animals at particularly high dosages of HMB.

Contraindications

When should HMB not be used?

The use of HMB is contraindicated in case of hypersensitivity to the active ingredient.

Pharmacological Interactions

Which drugs or foods can modify the effect of HMB?

There are currently no known pharmacological interactions between HMB and other active ingredients

Precautions for use

What do you need to know before taking the HMB?

Since there are no long-term research on children, nursing mothers and pregnant women, in these moments of life HMB should not be used spontaneously, but only after a preventive medical consultation.