Here Are 3 Side Effects of HMB You Should Watch For

When it comes to supplements that are backed up by science, HMB (beta-hydroxy-beta-methylbutyrate) is one of the best you will find in any dietary supplement catalog, just a notch below creatine and protein powders. As with any substance you put in your body in large quantities, though, you need to be concerned with how HMB will affect your overall health.

So, what kind of side effects should you watch for when taking HMB?

Let’s take a look at what the compound is and how it acts in your body to find out.

What Is HMB?

Leucine is a branched-chain amino acid that has been shown to boost protein synthesis in humans. It’s also been shown to slow down proteolysis, or muscle breakdown, but only in quantities larger than those required for the synthesis effect.

Studies have found that’s likely due to the presence of HMB, a metabolite of leucine that forms when the amino acid is burned for energy or during protein synthesis. Like leucine — though to a lesser extent — HMB also shows an ability to improve protein synthesis.

So, HMB is a natural substance in your body, but we only produce about half a gram — at most — per day. Studies indicate we need at least three grams per day in order to produce positive results in terms of protein balance.

What Does Science Say About Side Effects

While there are plenty of studies that show HMB to be effective in promoting gains in lean mass and strength, there are several that failed to produce improvements. The reasons for that discrepancy seem to revolve around the extent of relative muscular damage involved, as advanced lifters are often just “maintaining,” and they’re typically the ones who are non-responders to HMB.

What is really remarkable about the literature around HMB is that virtually none of the studies have identified any negative consequences  of HMB supplementation. Still, there are a few  side effects of HMB that are considered beneficial for most but COULD be a problem for some lifters in extremes cases:

  • Lowered Cholesterol – HMB has been shown in some studies, such as those discussed in this 2008 literature review,    to affect cholesterol production. Usually, this means lowering LDL and total cholesterol. That’s generally  a good thing for most Americans but may be a problem if you already have low cholesterol since it’s essential for healthy cells and proper hormone function. The mechanisms for how HMB affects cholesterol are also not yet completely understood.
  • Reduced Blood Pressure – Other studies, like those reviewed by researchers from Iowa State University in 2000, found that HMB can reduce blood pressure in some subjects. While this is again a beneficial effect for many subjects, it could be a problem if you already suffer from low blood pressure.
  • Weight Gain – Many of the studies into HMB, including those mentioned above, indicate a gain in lean mass for many subjects. This is desirable for most bodybuilders and athletes, of course, but it could be detrimental to your goals if you have joint problems or are involved in a sport that requires you to maintain your weight below a certain threshold — wrestling, boxing, etc.

Even outside of targeted scientific studies, most experts have found little reason to knock HMB on the safety front. Even WebMD rates it as possibly safe, though they do caution against using HMB for pregnant or breast-feeding women.

In the end, there just isn’t much evidence that HMB is dangerous for you, but there is not an avalanche of research into its side effects. You should consult with your doctor before beginning to use HMB, and follow up frequently for more blood tests and consultations. Only you and he can decide whether HMB will be a problem for you.

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