As an amino acid or a “building block of life,” isoleucine plays a key role in forming proteins, breaking down food and providing energy while also aiding growth and healing processes. It also plays a key role in blood sugar regulation.

Even though isoleucine is considered essential to human health, it can’t be made by the body. As a result, older adults tend to be more likely to experience an isoleucine deficiency. Symptoms of a deficiency include muscle wasting and muscle tremors. So how do you obtain this vital organic compound? You can get it from your diet through consumption of healthy foods like grass-fed beef, Swiss chard and sesame seeds or in supplement form.

What Is Isoleucine?

Isoleucine, also referred to as L isoleucine or L-isoleucine, is an amino acid. The three-letter isoleucine abbreviation is “lle” and the one-letter abbreviation is simply “l.”

Who discovered isoleucine?

The German chemist, Felix Ehrlich, is credited with discovering it in hemoglobin in 1903.

What type of amino acid is isoleucine?

It’s an essential amino acid. This means that it is very much needed by the body to function optimally yet the body cannot produce it on its own.

Is isoleucine polar?

The isoleucine side chain is hydrocarbon, which classifies it as a non-polar or uncharged amino acid.

Is isoleucine acidic or basic?

It’s considered to be neutral.

Isoleucine structure is what makes it a branched-chain amino acid or BCAA. Leucine, isoleucine and valine are all considered BCAAs because of their similarly structured side-chain.

Whats the difference between BCAA and EAA?

The three BCAAs are also three of the nine essential amino acids, or EAAs. So BCAAs are a subgroup of EAAs.

Will BCAA make me fat?

Actually, BCAAs have a reputation for being fat-fighting.

What does leucine isoleucine and valine do?

As BCAAs, they all prompt the construction of protein in muscle and may also decrease the breakdown of muscle.

What is the difference between isoleucine and leucine?

If you’re comparing leucine vs. isoleucine, both leucine and isoleucine are branched-chain amino acids. This means they have a similar chemical structure. Compared to the other two BCAAs, isoleucine falls in the middle for its ability to cause muscle protein synthesis because it’s stronger than valine yet a lot weaker than leucine.

Where is isoleucine found in the body?

In the human body, it’s mainly concentrated in the muscle tissues.

What is the function of isoleucine?

It plays a role in hemoglobin synthesis. Hemoglobin is the protein molecule in red blood cells that carries oxygen from the lungs to the body’s tissues. Isoleucine is also key to the regulation of energy and blood sugar levels. The isoleucine amino acid is also believed to mediate glucose uptake into a cell and break it down into energy. This specific isoleucine function is why it may help to enhance athletic performance and also act as a hypoglycemic agent.

Health Benefits

What is L-isoleucine good for? Benefits include:

1. Lowers Glucose

Could this amino acid be helpful to diabetics and other people trying to keep their blood sugar levels under control? Research using normal animal subjects reveals that just one oral dose of isoleucine significantly decreased plasma glucose levels, but administration of leucine and valine did not produce a significant decrease. It appears that isoleucine is able to stimulate the insulin-independent glucose uptake in skeletal muscle cells.

Another research study published in the Journal of Nutrition similarly found that oral administration of isoleucine, but not leucine, resulted in a significant decline in plasma glucose levels.

2. Decrease Muscle Damage and Soreness

Some bodybuilders and athletes take BCAAs for the possibility that they will decrease post-workout muscle damage and soreness. According to a systemic review published in 2017 in the journal Nutrients, some studies have shown that BCAAs supplementation can be successful at reducing exercise-induced muscle damage. Results seem to be most effective when muscle damage is low to moderate and the supplement is taken before exercise.

3. Reduces Fatigue and Boosts Performance

Many people are looking for new ways to reduce post-exercise fatigue. A study published in the Journal of Nutrition reveals how ingestion of BCAAs by human subjects during a standardized cycle ergometer exercise resulted in lowered ratings of perceived exertion and mental fatigue. BCAAs appear to limit the uptake of tryptophan by the brain while also reducing synthesis of 5-hydroxytryptamine (5-HT) in the brain, which is another factor that has been suggested to cause fatigue. This study also demonstrates how BCAAs can help boost both physical and mental performance.

Foods and Supplements

What foods contain isoleucine? These are some great sources:

• eggs
• dairy products like cottage cheese
• spirulina
• turkey
• lamb
• chicken
• grass-fed beef
• seafood (including tuna, cod and haddock)
• watercress
• chard
• lentils
• black beans
• pinto beans
• sunflower seeds
• sesame seeds

What foods have leucine isoleucine and valine? These branched-chain amino acids can be found in foods like:

• whey protein
• grass-fed beef
• chicken
• wild-caught fish
• cage-free organic eggs
• lima beans
• chickpeas
• lentils
• brown rice
• almonds
• Brazil nuts
• cashews
• pumpkin seeds

You can also take this essential amino acid as a standalone supplement. However, it’s typically recommended to take a balanced branch-chain amino acids supplement that includes all three. Whey protein is another supplement option that contains all three BCCAs.

Recipes and Dosage

Looking to get more of this amino acid in your diet? These healthy recipes have high-isoleucine foods and are a tasty way to up your daily dose of this essential amino acid:

• Garlic Baked Chicken Recipe
• Tuna Pasta Salad with Kalamata Olives and Cherry Tomatoes
• Black Bean Brownie Recipe

As a supplement, it can be taken alone, but it’s recommended to take it along with the other BCAAs, L-leucine and L-valine. A common recommendation is to look for products that have a 2:1:1 ratio of leucine: isoleucine: valine.

Risks and Side Effects

Possible side effects of supplementation with BCAAs  include nausea, vomiting, diarrhea, stomach bloating, fatigue and loss of coordination. Rarely, branched-chain amino acids can lead to high blood pressure, headache or skin whitening.

Using a single amino acid supplement can cause a negative nitrogen balance in the body, which can decrease how well your metabolism works and cause your kidneys to work harder. For children, supplementing with a single amino acid may lead to growth problems. It’s generally not advised for anyone to take high doses of single amino acids for long periods of time.

Women who are pregnant or breastfeeding should not supplement with L-isoleucine.

The inability to break down isoleucine and other BCAAs is associated with an inherited condition called maple syrup urine disease or MSUD, which causes urine to be discolored and smell sweet similar to maple syrup. MSUD can be mild or come and go, but even in its mildest form, repeated periods of physical stress can cause mental disability and high levels of leucine amino acid to buildup. Severe cases of MSUD can cause brain damage as a result of periods of physical stress, including fever, infection or not eating for a long time. Someone with MSUD should not supplement with BCAAs.

Talk to your health care provider before supplementing with this essential amino acid, especially if you have a medical condition and/or currently take medication.

Final Thoughts

• L-isoleucine is an essential amino acid that the body cannot manufacture so it must be obtained through diet or supplements.
• It’s not hard to get this amino acid in your diet by consuming foods like meat, fish, dairy products, legumes and seeds.
• Based on research to date, benefits of this essential amino acid may include lowered glucose levels, improved cognitive and physical performance, and reduced post-workout fatigue.
• It is most often taken as a supplement in combination with the other two branched-chain amino acids, L-valine and L-leucine.
• Whey protein is a supplement that contains all three branched-chain amino acids.
• Always consult with your health care provider before supplementing with amino acids.