Hydroxymethylbutyrate (HMB) is a chemical that is produced when the amino acid leucine is broken down by the body.
It has a few different names depending on the specific version of the molecule. Other names include beta-hydroxy beta-methylbutyric acid, beta-hydroxy and beta-methylbutyrate.
The human body naturally produces it, but typically only produces around 0.3g per day on average. When people supplement it, standard dosages are usually 3-6g per day.
Interest in HMB supplementation started in the early 2000s when a few studies showed significant gains in muscle and strength in comparison to placebo.
There have even been two later studies that have shown gains that are better than what even moderate dosages of steroids provide. So obviously this has generated some interest.
Other research has not been quite as positive. Since the research looks so mixed, this post is intended to summarise whether HMB can be helpful or not.
How Can HMB Theoretically Help?
Supplementing with HMB has been shown to reduce muscle damage and muscle protein breakdown, which obviously can align with the goal of hypertrophy and strength gain.
This mechanism is even stronger for certain phases of training where volume and intensity is significantly higher than normal, and more muscle damage is occurring.
Arguably, this is part of why the research in relation to untrained lifters has typically been significantly more positive than the research on well-trained lifters.
At minimum, long-term HMB supplementation has been shown to be safe. So either it helps a bit, or at least there are no downsides beyond the cost and mild inconvenience of taking it.
Research On Untrained Lifters and Older Populations
Most of the studies on HMB showing significant gains in muscle have been performed on untrained lifters.
Some examples of this are the following studies:
- Beta-hydroxy-beta-methylbutyrate ingestion, Part I: effects on strength and fat free mass
- Effect of leucine metabolite beta-hydroxy-beta-methylbutyrate on muscle metabolism during resistance-exercise training
- Nutritional supplementation of the leucine metabolite beta-hydroxy-beta-methylbutyrate (hmb) during resistance training
- Creatine and beta-hydroxy-beta-methylbutyrate (HMB) additively increase lean body mass and muscle strength during a weight-training program
This makes sense since untrained lifters typically accrue more muscle damage than trained lifters. Decreasing the damage and muscle protein breakdown could increase the amount of muscle growth that can occur.
For older populations, the proposed mechanism is that as we age, it becomes easier to lose muscle.
Since HMB is mainly beneficial for reducing the muscle breakdown side of the muscle growth equation, it is more likely to be beneficial under circumstances where people are more prone to muscle loss.
It is still a little hit and miss with older populations. One review of 7 studies that covered 287 older adults found HMB led to small amount more muscle growth than those who received a placebo. To be specific, the gain of lean mass was only 0.35kg more over 8-12 weeks on average.
Making it look even less effective, a review of 10 studies, covering 384 adults over the age of 50 also found little to no effect.
Research on Trained Lifters
A systematic review from 2014 covering all of the studies on trained athletes identified that some studies showed no benefit of HMB on strength and muscle growth and others showed a “trivial” benefit.
The mechanism also makes far less sense for trained lifters than it does for newer lifters. Trained lifters typically experience less muscle damage than newer lifters. Although if you switch training routines or quickly increase volume, this point might become relevant again.
Normally I am in the camp of “if something might work a bit and you are okay with the costs and adding the supplement into your routine, maybe it makes sense for you to take it.” So, the trivial aspect could be worth it for some.
But with HMB there are a few other things to factor in:
- It is quite an expensive supplement in comparison to a lot of other supplements.
- The consensus from most evidence-based practitioners is to downplay the effectiveness of it, based on looking at the totality of evidence and the mechanisms.
- There really is not even a lot of anecdotal support for it. Not many people actually take it, in comparison to the amount of people who swear by other supplements. When things work, usually people start implementing whatever it is that works, before the research actually supports it.
- There is controversy amongst some of the studies which should raise scepticism.
A great example of the second point can be seen in the below video from Omar Isuf and Mike Israetel:
The current consensus is that if protein and leucine intake are high enough, HMB is unlikely to further help trained lifters.
Controversy in Studies On HMB
The biggest reason why there has been hype behind HMB is that there are two studies that show extremely positive results. They are massive outliers, and to be honest, seem too good to be true.
As mentioned, the mechanism makes sense for newer lifters, but not as much for well-trained lifters. And that is mostly what we saw in the research until around 2014.
Then out of nowhere, one study showed that a group taking HMB was able to gain 7.4kg of lean mass over 12 weeks while dropping their body fat percentage by 6.6%.
Muscle gain and fat loss like that is unheard of without high dosages of steroids.
This same group then published a second study showing even more insane results with 8.5kg of lean mass gained while dropping 8.8% body fat while using HMB and an ATP supplement.
These studies were both done in well-trained lifters.
For context, the below image from Joseph Agu of Elite Nutrition Coaching sums this up well. It compares a study on lifters using 600mg testosterone (a moderate dose steroid cycle) for 10 weeks to studies from this group on ATP alone, HMB alone and HMB + ATP.
Is it not absurd that a supplement that has been around for a long time and is not overly popular, could be more effective than moderately dosed steroids?
To drive another nail into the coffin the placebo group in the testosterone study made better progress than the placebo group in the HMB study. This means that the intervention of the HMB supplement is what is identified as making the difference. The below image from Stronger by Science illustrates this well.
This is such an outlier result that unless it is consistently replicated by other groups, it makes sense to almost completely ignore it. If almost all studies show one thing, and one study shows another, it makes sense to go with what the majority show.
Research on Other Areas
HMB might have benefits for other areas such as sarcopenia related to medical conditions.
In conditions where muscle loss is common, taking HMB appears to be more effective than placebo at preventing this muscle loss. This can be part of why some nutritional supplements used in hospitals such as Ensure contain HMB.
There is also a small amount of evidence that HMB can improve aerobic and anaerobic outcomes. It is early days with this research though and is not an area which is well studied as of yet either. And it also seems to be relatively uncommon amongst the endurance athlete community too.
How to Take HMB?
If choosing to take HMB, the best way to do it is typically to take ~3g of HMB, 30-120 minutes before training sessions for acute effects in terms of minimising muscle damage.
For the chronic effects, splitting this dosage over 3 servings per day appears to be the best strategy.
As with most supplements, dosage is really based on how large you are and how much muscle mass you have. Larger people will likely require more than 3g, smaller people likely require less.
Technically 38mg of HMB per kg of body weight is the consensus dosage, which comes out around 3g for an 80kg individual.
Thoughts on Whether HMB is Beneficial
If you take those two outlier studies out of the equation, HMB is a supplement that likely is mild-moderately beneficial for untrained lifters who are now training regularly. It is also likely beneficial for those who are at risk of muscle loss due to bed rest or medical situations.
The main reason it has not gained traction in the evidence-based community or amongst lifters, in general, is because it does not seem to have much if any, benefit for trained lifters.
If you still wanted to take it though, there is no noticeable downside beyond cost and the actual process of taking it.