What is HMB
HMB, otherwise known as beta-Hydroxy beta-methylbutyric acid is a compound that your body creates during the break down of the amino acid Leucine, one of the protein building blocks. HMB is metabolised from Leucine by liver enzymes at a rate of around 5% [1], meaning that supplementing with BCAA's or Leucine alone is not effective at chronically raising HMB levels.
What does it do
There are several different vectors to which HMB acts, one of which is through HMB as a precursor to a rate limiting enzyme to cholesterol synthesis HMG-coenzyme A reductase. [2] This is important because when we exercise, we cause damage to the muscle cell membranes of which a part of it is made up of lipids and cholesterol, which it requires to then repair its self, [3] it has been suggested that damaged muscles cells may lack adequate cholesterol to complete various cell functions. [5] This all has to happen before muscle protein synthesis of contractile tissue occurs, effectively meaning that dietary fats and cholesterol can act as a rate limiting factor for muscle hypertrophy. [4]
This will sound like I'm harping on a meme here, but the old adage of "gotta confuse the body, right babe?" [6], may actually have some standing in HMB supplementation. HMB seems to only exert its positive effect through repairing muscle cell membrane damage induced from novel exercises, through activation of three major pathways through which proteolysis occurs are lysosomal, calcium activated calpain (CAC), and Ub-pathways. The UB pathways are often seen to be active in new trainees, people returning from long term exposure of 0 gravity, [7,8] exercise induced states of catabolism [9] and other states that have either induced muscle wasting or stagnation. This is key to note, as trainees who supplement with HMB for sustained periods of time have subsequent less UB activation with each successive bout of repeated exercise. [10] This is why I brought Rich into this and why I want you to keep the UB pathway in mind when we discuss the effects in studies later on.
Lean body mass
There are dozens of studies out there, all touting how effective HMB is at building lean muscle mass [11,12,13,14,15] to name just a few and also studies showing negligible to no effect [16,17,18,19,20]. Though on the surface this may be confusing, I actually think this is to be expected from what we know already.
We know that HMB works via repairing damaged muscle cell membranes allowing for muscle protein synthesis to occur at a normal rate. This damage is generally worse when new stimulus has been applied. The obvious conclusion is that, if the body is being put under a new stressor that it isn't used to it will experience the "increase" muscle protein synthesis with HMB supplementation, but if it us "used" to the stimulation then less damage will occur resulting in a normal amount of muscle protein synthesis, that it would otherwise produce. HMB does not push synthesis above and beyond a normal range, more make up for what would of otherwise been.
In the studiesI referenced, there have been that have shown benefit for highly trained athletes, this fits into the conclusion from a recovery standpoint. Continually stressing muscles without enough rest will result in over training, aka decreased muscle protein synthesis from overly damaged muscle cells [21]. Supplementation here may allow for an increase in chronic training levels often seen in athletes.
Strength and endurance.
I won't repeat what I mentioned in the previous section, but the same logic applies here as well. With the increased recovery of athletes pushing their bodies to the extreme will account for the strength and endurance increase they see, the same for the new trainees seeing gains above and beyond what their placebo group is already experiencing.
I do have to stress here that the benefit seen from the trained individuals is by potentially offsetting overtraining induced reduced muscle protein synthesis. If you are an average gym goer do not expect mind blowing strength gains and endurance when supplementing with with HMB unless you are really putting the effort in.
Body Fat
A few of the studies previously mentioned have show a minimal decrease in total fat mass, this can be explained simply by the well known mechanisms of total metabolic rate. As you put on more muscle mass, your body will require more calories to maintain the size. HMB has no fat oxidisation quality's of its own, more of a slight downstream effect.
Dosing
Most studies advise taking 3 grams of HMB daily for maximal benefit [22,23,24,25,26]. A dose dependant effect has been seen through 0, 1.5 and 3g, with 3 grams coming out as the most efficacious. A more recent study found that 6g of HMB did not offer benefit over the standard dose of 3g, it instead offers a dosage scale of 38 mg/kg for efficacious dosing. [27]
HMB has a half life of approximately 2.5 h, and reaches baseline levels 9 hours after consumption, [28] it is currently a hot topic on when and how to dose HMB. A lot of online sellers recommend it as a postwokrout supplement, but current evidence suggests that an even dose go 1g 3 times a day to be the most efficacious [1] as a greater percentage of HMB is retained at 1g against 3g. [28]
Side effects
At stated doses the International Society of Sports Nutrition recommends HMB to be generally safe. [29] But as always, ask your doctor if you have any concerns before starting a supplementation regime.
Bottom line
Though I do not take HMB my self, (I may experiment with it in the future) it seems to me that in order for this supplement to give us any benefit we need to be going above and beyond what we normally do. In this case, I can see its benefit in highly trained individuals engaging in an extremely rigorous exercise regime that requires increased recovery or for individuals being exposed to new muscle stressors. HMB becomes much less attractive to those applying steady progressive overload style training where our body has adapted to the stimulus and is engaging in normal muscle protein synthesis which would not be effected noticeably by HMB.
parting words
I hope you enjoyed this breakdown of HMB as it was a fairly interesting subject to dive into. Let me know if you spot any mistakes in my citations, gramma etc. I'm by no means perfect and occasionally miss spelling mistakes or links!
Regardless, I'll hopefully see you on Monday for the 1 week Turkesterone log summary + my initial blood marker results!