Essential Supplementation - HMB: Hype or Help?

[01dragonslayer]

What is HMB?​

HMB is a metabolite of the amino acid Leucine. Basically that means your body turns leucine into HMB.

With touted benefits such as increased lean body mass, improved strength, and improved body composition, let’s see exactly what the science says about HMB.

Your Body is an HMB Factory​

Research has shown that HMB production is correlated with leucine intake1. Essentially, you are a regular ol’ HMB making factory. While you can get increased HMB through leucine supplementation, it's a horribly inefficient process as only 5% of leucine is converted to HMB1.

Imagine if you only got 5% of your paycheck!

HMB supplementation basically gives you the other 95% back. You can increase your HMB levels by taking it in supplement form. Well who cares…I mean what the heck is HMB and what does it do? And more importantly can it help you increase muscle and strength? (see what I did there?)

How Does HMB Work?​

Since HMB is a small molecule, it's important to explore what molecular mechanisms it is involved in. Put your science hat on, it’s time to get nerdy.

Firstly, it is well documented that HMB activates mTOR, a key “muscle growth” signaling molecule.2, 3, 4 HMB also activates another critical component in muscle protein synthesis, the very appropriately named P70S6K (seriously….who came up with that name)5.



In addition to increasing signals for muscle growth, HMB is also known to reduce the process in your muscles that is responsible for muscle-protein breakdown6.

Does HMB Give Results?​

The nerdy lab stuff is one thing; results in the real world are another. Does HMB deliver any actual benefit? Let’s take a look at the research as a whole and draw some conclusions.

Unlike many supplements, HMB has been tested in a lot of different people. We are talking trained and untrained, male and female, old and young. It has also been tested in different training modalities, with and without dietary intervention.

Looks like research in our field is really starting to get legit.

This amount of research does 2 things: 1) gives us the ability to draw more generalized conclusions, 2) makes data interpretation a nightmare and requires substantial thought and insight.

Despite the wide range of the studies, we can make some good conclusions from the data available.

HMB in Untrained Individuals​

Most of the research in untrained individuals has been conducted in the 4 to 8 week time frame. In the shorter studies that lasted 4 weeks, individuals who took HMB had bigger increases in fat-free mass (FFM) than those who took the placebo7, 8. Have we hit the gold mine?

Well, unfortunately when you look at the longer studies (8 weeks), HMB is not any more effective than placebo9. What gives? It is likely due to a problem with the research methodology.

Most of the 8 week studies did not include any type of periodization, this may have slowed the muscle growth of the HMB group which “adapted” sooner. They may have reached the same point because the stimulus for the HMB group at 4 weeks was similar to the placebo by 8 weeks.

At least that is my most educated guess. . . and there is some evidence to back it up. In a 12 week intervention study with periodization, HMB supplementation lead to greater improvements in lean mass and muscle strength than placebo10.

Another thing we should point out is that there appears to be a dose-response curve where increasing the dose from 1.5g to 3g led to greater increases in FFM. No one has looked at doses higher that 3g/day. . . . can I get some volunteers?!

HMB in Trained Individuals​

Now if you are reading Muscle & Strength you are probably a “trained” individual, so you will care more about this section.

What’s weird/interesting is that we see the opposite effect of HMB with respect to time relating to the trained athletes. HMB does not elicit greater improvements in the short-term, but it does in the long-term.

There have been a host of poorly-controlled studies which give almost useless data for drawing conclusions. As a scientist by training this kind of stuff drives me insane. So I will focus on the well-controlled ones.

A short-term (4 week) study found no improvements in strength or lean mass with HMB supplementation in college football players, but a longer-term study (7 weeks) using trained individuals shows that HMB supplementation lead to a 4.5 kg (9.9 lb.) increase in the bench press, and a 3.2 kg (7 lb.) increase in their squat, when compared to placebo11. So based on the research we have to date, this is the picture of what might happen with HMB supplementation in trained individuals.

HMB in Caloric Restriction​

Caloric restriction: a fancy word for eating like a rabbit. But seriously caloric restriction and building muscle don’t usually go hand in hand. However, sometimes we want to lean out and the only way to do that is to cut calories (find another way and you will be the richest person on the planet…I'm talking Zuckerberg rich).

Remember earlier that HMB has been shown to reduce catabolism. So maybe HMB could be effective in preserving muscle mass during times of caloric restriction.

I wish I could offer a glimmer of hope here, but the science isn’t on our side. One study found that 3g of HMB supplementation had no real effect on preventing lean mass loss and only slightly prevented decreases in power output in trained judo athletes12.

Again, my inner scientist is frustrated because the study only lasted 3 days which makes gleaning any real usable information difficult.

Another study that lasted 28 days also showed no benefit of HMB on muscle catabolism in Division 1 football players13.

The Final Word on HMB​

HMB is interesting. It appears to be most effective for increasing lean mass during early stages of training in untrained individuals and at improving strength over longer training periods in trained individuals.

Currently, the amount of evidence is pretty wide but not really deep. It looks hopeful, but more studies need to be done in a well-controlled manner to determine how much of an effect HMB has and whether it is repeatable in well-controlled conditions.

Here is my personal opinion. Give it a shot. Take detailed notes and conduct a self experiment. If it works run with it. If it doesn’t, move on to the next tool in your arsenal.