HMB: Benefits, Side Effects, Best Time to Take It & More

HMB

(Hydroxy-MethylButyrate)

Evidence: High
Possible Benefits: Low
Safety: Reasonable

What is HMB?

HMB is a metabolite of leucine, one of the 3 branched-chain amino acids (BCAAs), along with valine and isoleucine. As a supplement, HMB is often used to improve muscle protein synthesis and reduce muscle loss over time. Per gram, HMB is about 20 times more potent for preserving muscle mass than L-leucine and about as effective for muscle protein synthesis. This article is about the main benefits of HMB, its potential side effects, the best time to take it, and more.

What does HMB do for the body?

HMB is an active metabolite of L-leucine.

It is highly anti-catabolic, which means it helps preserve muscle mass and lowers the rate of muscle loss.

In the body, leucine is the main activator of protein synthesis. HMB is about as effective for this purpose as L-leucine.

Cells turn on protein synthesis through the mammalian target of rapamycin (mTOR) based on leucine levels. The higher the leucine levels in the body, the more this enzyme gets activated.

Despite the increase in muscle protein synthesis, long-term supplementation of L-leucine or HMB does not lead to increases in muscle mass in most cases.

However, HMB supplements can protect muscle catabolism to at least some extent.

Possible benefits

It is important to note that all of the potential benefits mentioned below are dose-dependent. Generally, the higher the dose, the more pronounced the effects are. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.

Major benefits

Reduced muscle catabolism – HMB is about 20 times more effective for reducing muscle catabolism (muscle loss) than L-leucine. In other words, 1 gram of HMB is about equal to 20 grams of L-leucine for this purpose.

Minor benefits

Improved carbohydrate absorption – HMB promotes insulin secretion from the pancreas and helps the body utilize carbohydrates. Taking this supplement before a carbohydrate-rich meal lowers the blood glucose spike from it.

Possible side effects

These side effects are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to very high doses.

Toxicity – While acute toxicity has never been reported, taking high amounts of HMB could lead to chronic toxicity and cause some health problems. For example, doses over 3 grams may increase serum ammonia and urea. To prevent chronic toxicity, it is best to stay below 3 grams a day unless you have a great reason to take more.
Contamination – Contaminated supplements are uncommon in the USA and other well-regulated countries. However, if you wish to buy products from China, India, or other countries without strict regulations, beware that the supplements may be contaminated. Either way, you need to choose the brand you order from wisely. It is highly recommended to check the certificates or read through some reviews for the specific product before you buy it. The FDA (Food and Drug Administration) has the power to regulate dietary supplements but can only do so after they have been on the market for a while. That’s because supplement companies are not obligated to announce to the FDA when releasing a new product on the market. The FDA has to discover the product and test it for potential impurities, which can take a lot of time. During that time, the supplement can be sold on the market even if it’s impure. Also, supplement companies can change their manufacturers without announcing it to the FDA.

Who should not take HMB?

You should probably avoid taking the supplement if you:

eat high amounts of protein from food (most whole foods contain at least some amount of each essential amino acid including L-leucine, a precursor to HMB)
experience a severe adverse reaction after taking the supplement
are on a tight supplement budget (since there are more cost-effective supplements on the market for most people)

Who will benefit the most?

You should consider taking the supplement if you:

consume very little protein (less than 0.3 grams/pound of body weight)
are muscular and work out a lot
are going through an offloading phase and want to prevent muscle loss
are an older person (older people need up to 2 times more leucine than young adults for similar activations of muscle protein synthesis)

How much HMB should you take?

HMB is an active metabolite of L-leucine. If you get enough leucine from food, you should not need to take HMB supplements.

The RDA (recommended daily allowance) for L-leucine is 42 mg/kg/day for all adult men and most adult women. This is enough for the majority of people to prevent any symptoms of deficiency.

The RDA increases to 56 and 62 mg/kg/day for pregnant and lactating women, respectively.

Since this amino acid is in almost every food, you probably already get sufficient amounts from food alone. About 0.36 grams of protein/pound of body weight should be enough to prevent a deficiency.

If you plan to take HMB as a supplement, 1-2 grams appear to be the best daily target for most people. This amount should provide most of the benefits without meaningful side effects.

Some people may benefit from doses higher than 2 grams. These include older people, bodybuilders, very physically active individuals, and those on a low-protein diet.

The upper safety limit for HMB is not well-established. Up to 3 grams daily seem to be safe in humans with little to no health consequences. However, even lower amounts can cause some health problems if you take the supplement for a prolonged period.

To stay on the safe side, don’t take more than 3 grams daily unless you have a great reason to do so.

Food sources of leucine

L-leucine is found in all whole foods that contain dietary protein.

The amount of leucine per gram of protein varies from food to food but a general rule of thumb is that the more protein you eat, the more leucine you are getting from food.

The easiest way to find out exactly how much leucine or other amino acids you are getting from food is with Cronometer.com. This free app allows you to track all vitamins, minerals, and more.

Best time to take HMB

HMB is water-soluble, so you don’t have to take it with food to absorb it well. Taking the supplement with food is better if it causes stomach upset when you take it on an empty stomach.

To maximize the benefits, take HMB before or right after a workout.

Whether you take the supplement in the morning or the evening doesn’t matter. It should not interrupt your sleep in any way.

If you practice time-restricted eating, take this supplement during your eating window to guarantee it won’t break your fast.

Interactions

Carbohydrates
HMB promotes insulin secretion from the pancreas and helps the body utilize glucose. Taking this supplement before a carbohydrate-rich meal lowers the blood glucose spike from it and increases muscle protein synthesis.
Isoleucine
Leucine and isoleucine act synergistically with each other and have to be kept in balance. Since HMB is an active metabolite of leucine, you may benefit from taking the supplement together with isoleucine.
Other amino acids
All essential and non-essential amino acids need to be kept in balance as they act synergistically in many ways. Too much of one amino acid can sometimes cause side effects without enough of another amino acid. That is most notably the case for glycine and methionine, but the principle applies to other amino acids, such as lysine and arginine, and the BCAA trio. Using a single amino acid supplement may lead to a negative nitrogen balance, which can lessen how well your metabolism works. A protein powder is usually a better choice for getting enough amino acids unless you have a specific goal in mind targeted by a particular amino acid/s.
Resveratrol
Both resveratrol and HMB can activate the SIRT1 gene and act synergistically in doing so when taken together. Whether or not this effect is of practical significance is not yet clear.

Where to buy HMB

Amazon is the best option for ordering HMB supplements in most countries. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the internet.

Beware some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.

FAQ

You can take the supplement daily and do not need to cycle it. However, it is certainly not a problem if you don’t take it daily. Not taking the supplement every once in a while could lead to better absorption. That is yet to be proven or disproven.

All of these options are fine. The two most important things to consider are the price and dosing. Powders are almost always the cheapest form. However, you may need a highly accurate scale to dose them correctly (preferably 0.001g). You can get one for as little as $20 from Amazon. Dosing the powders also takes some time that can add up over months or years. The disadvantage of capsules is that they often contain bovine gelatin, which rarely comes from an ethical source.

Yes. HMB absorbs and digests well if you take them before falling asleep. The supplement should not impact sleep quality in any significant way.

This supplement should not become harmful once it exceeds the expiration date but can lose potency over time.

Keep the supplement in a cold, dark, and dry place, and it should remain just as potent for many months or even years.

While toxicity is rare, too much HMB in the system can cause some health problems, often related to increasing the levels of ammonia and urea. It is best to stay below 10 grams a day to prevent these side effects.

You may need more HMB if you:
– eat very little protein (less than 0.3 grams/pound of body weight)
– are muscular and work out a lot
– are going through an offloading phase and wish to preserve muscle mass
– are an older person (older people need up to 2 times more leucine than young adults for similar activations of muscle protein synthesis)

The half-life of HMB in the body is about 2.5 hours. It stays in your system for 12-16 hours after you consume it.

If you take the supplement before a workout, you may notice a mild increase in power output. In the long term, you need to take the supplement for many months to begin noticing the benefits.

You can easily find vegan-friendly HMB pills and powders but always check the label to be sure. If you buy the supplement in a capsulated form, beware that the capsules often contain animal-based gelatin. Instead, find a brand that puts its products into cellulose capsules.

HMB is water-soluble, so you don’t have to take it with food to absorb it well.

While low doses may not break a fast, higher doses certainly can. If you practice time-restricted eating, take this supplement during your eating window so it doesn’t break your fast.

References

Most of the information provided in this guide is supported by scientific research that can be found and verified in the PubMed medical library. We highly encourage you to use the library to verify anything said in this article. We excluded from consideration studies that are either confounded or have a high conflict of interest.

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