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L-Isoleucine: Benefits, Side Effects & Dosage

L-Isoleucine
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What Is L-Isoleucine?

L-isoleucine likely isn’t a word you hear very often. But you would do well to familiarize yourself with it. Whether you want an athletic edge or simply a better diet, this amino acid could do wonders.

L-isoleucine is one of the nine essential amino acids and one of three branched-chain amino acids (BCAAs). So what are essential amino acids and BCAAs?

Essential Amino Acids

These are organic compounds that combine to form proteins (x). When the body breaks down proteins, amino acids are left. These then help the body break down food, repair bodily tissue and synthesize other proteins.

Amino acids are grouped into two categories — nonessential and essential. The body synthesizes nonessential amino acids, which means it doesn’t need to acquire them from food or supplements.

On the other hand, our bodies don’t make essential amino acids; the body must acquire them from food or supplements. There are nine essential amino acids — histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.

When we get cuts and scrapes, our bodies need amino acids to heal. Our bodies also use them to regulate blood sugar (x). Though the market for amino acids, and BCAAs especially, seems to favor athletes, these supplements can be valuable dietary inclusions to anyone.

Branched-Chain Amino Acids (BCAAs)

BCAAs are comprised of three essential amino acids — leucine, isoleucine and valine (x). You may have read about them before, so why are they such a popular topic?

BCAAs are involved in energy production, protein synthesis and muscle-protein synthesis (x). Many athletes use them as a nutritional supplement to alleviate muscle damage after exercise and promote muscular anabolism (net gain in muscle protein) (x). Research has also shown that they help mediate the uptake of glucose into our skeletal muscles.

L-Isoleucine in BCAAs

Isoleucine has a wide range of physiological functions in our bodies (x). It helps our bodies by supporting wound healing, detoxifying nitrogenous wastes, such as ammonia (a toxic byproduct we pass in our urine), forming hemoglobin, regulating blood sugar and secreting hormones.

It’s best to take L-isoleucine with the other two BCAAs, according to a study published in the Journal of Nutrition (x). By taking these amino acids together, we help our bodies maximize their ability to mediate glucose uptake in our resting skeletal muscles and cells (x).

So why should we care about consuming enough essential amino acids? Well, our bodies and all the cells within them need these amino acids to function optimally. So it’s essential (pun intended) we give our bodies the amino acids they need.

L-Isoleucine Benefits

Athletic Performance

One study found that a mixture of amino acids, which included isoleucine, improved training efficiency in rugby players (x). Researchers found positive change in muscle integrity and hematopoiesis (the formation of blood cells) in these athletes. The study concluded that amino acids not only supported muscular fatigue recovery, but also increased the blood’s oxygen-carrying capacity. This likely helped these athletes improve their performance.

A key takeaway is that isoleucine helps muscular recovery. The more recovered you are after training, the better your next workout will be. Rest is just as important (if not more so) than the training itself.

There’s plenty of research on the effects of amino acids and BCAAs on exercise performance. But the scientific community on the whole still debates whether amino acids alone are responsible for muscle synthesis post exercise. And there’s an argument to be made. Which BCAA is better for building muscle? Isoleucine or leucine?

Leucine has shown to outperform isoleucine in muscle-protein synthesis (x). Isoleucine, on the other hand, outperforms not only leucine, but also valine (another BCAA) in increasing glucose uptake into muscle cells.

Protein Synthesis

BCAAs promote an anabolic response in muscles and decrease the rate of protein degradation. Researchers have found that BCAAs consumed before and after exercise initiate adjustments to protein synthesis by making changes to signaling pathways involved in protein synthesis (x).

They’ve also found that leucine produces a better response in protein synthesis than its BCAA counterparts. But taking leucine alone isn’t enough. Therefore, the study suggests that taking all three BCAAs together achieves desired protein-synthesis results.

Blood Sugar Regulation

Isoleucine is essential for blood-sugar regulation, and isoleucine deficiencies can mirror the effects of hypoglycemia (x).

L-Isoleucine Benefits

L-Isoleucine Side Effects

As with any medication or supplement, taking amino acids may cause side effects. It’s important to know ahead of time what you may feel if you take them. Some studies have suggested that BCAAs are safe for both children and adults to take for up to six months (x). Side effects may include fatigue, nausea and muscle incoordination.

Several groups of people should talk to their doctors before taking BCAAs:

  • Pregnant or breastfeeding women
  • Heavy drinkers
  • Individuals with ALS or Lou Gehrig’s disease (x)
  • Individuals with branched-chain ketoaciduria (maple syrup urine disease) (x)
  • Individuals awaiting surgery
  • Individuals with kidney or liver problems

Talk to your doctor before taking BCAAs or other amino-acid supplements if you’re worried about a current or preexisting medical condition.

L-Isoleucine Recommended Dosage

As with taking any supplement, it’s important to understand dose guidelines. It is best to start by taking 1 to 2 grams up to three times daily (x). If your goal is to build muscle, consider taking isoleucine with leucine and valine or taking BCAAs.

L-Isoleucine Food Sources

If you’re interested in increasing your dietary intake of isoleucine, try eating more pork, beef, chicken and fish (x). If you’re vegan or vegetarian, try high-protein plant-based foods such as legumes, seeds and wheat germ.

The Bottom Line

Is taking L-isoleucine right for you? Your doctor can help you determine the answer, especially if you have a current or preexisting medical condition. BCAAs are a great way to increase your intake of this amino acid and are especially beneficial to individuals looking to enhance muscle repair and recovery after workouts. L-isoleucine may also benefit individuals who need to monitor their blood sugar.

L-isoleucine supplements are easy to take and offer many benefits. Enhanced protein and muscle synthesis and glucose uptake are only some. If you’re looking for that extra training edge or to promote better muscular repair in your body, isoleucine and BCAAs may be right for you.

By: Bria Edwards

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Greg Murphy


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