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What Are the Functions of Leucine?

By Alison Darrow

Leucine is one of three essential amino acids that increase muscle mass and help muscles recover after exercise. It also regulates blood sugar and supplies the body with energy. These functions make it invaluable when the body is stressed. Leucine is used clinically to help the body heal, and it also affects brain function.

Building Protein

Unlike other amino acids, essential amino acids can’t be produced by the body, so we have to get them from food or supplements. Leucine and two other essential amino acids, isoleucine and valine, are needed to build protein. Because of their structure, they are called branched-chain amino acids, or BCAAs. Leucine is the fourth most abundant of all amino acids in muscle, and together the BCAAs makes up about a third of muscle protein. BCAAs fuel muscle metabolism and protect muscle from stress by stimulating protein synthesis, increasing reuse of amino acids, and decreasing protein breakdown under stress.

Regulating Blood Sugar

The body uses glucose, or sugar, for energy. Many amino acids produce glucose, but leucine is the only one that can substitute for glucose during fasting. Increased glucose prevents the body from using muscle for energy during intense workouts. Leucine is more effective at regulating blood sugar levels than isoleucine and valine, because they are converted to glucose more slowly.

Building Muscle

Leucine is also thought to stimulate insulin release. Insulin, an anabolic hormone, is needed to enable key nutrients, such as glucose, amino acids and creatine, to enter muscle cells. Insulin stimulates protein synthesis and inhibits protein breakdown. BCAAs are the primary fuel in anabolic reactions, so they provide a reasonable and safer alternative to steroids for body-builders, weight lifters, and other athletes. During training, they enhance muscle-protein metabolism, decrease exercise-induced protein degradation, and support oxidative metabolism in muscles during strenuous exercise.

Medical Uses

Stress states decrease BCAA levels. Surgery, trauma, cirrhosis, infection, fever, starvation and malnutrition stress the body, making protein break down faster than normal. BCAA supplements can prevent or reverse this effect. Intravenous solutions containing BCAAs are given to people recovering from trauma and surgery to help bones, skin, and muscle heal. In diseases that affect the muscles, BCAAs are used to decrease wasting. According to Medical News Today, recent reports also suggest that leucine supplements can prevent the muscle loss that comes with aging. Astronauts use them to help withstand the effects of space travel on the body.

Brain Functions

BCAAs are constituents of neuropeptides—biochemical messengers from the brain to the body’s cells—and neurotransmitters, like endorphins and enkephalins, which produce calming and pain-relieving effects. One form of leucine prevents these natural painkillers, produced by the body, from breaking down. Enkephalins may lower levels of serotonin and dopamine in the brain; however, and According to “The Healing Nutrients Within,” at least one study found very high levels of leucine in people with depression. BCAA supplements can help treat and even reverse hepatic encephalopathy, a brain condition related to alcoholism and severe liver or spleen disease.

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