Strong Performer

Leucine is a powerful part of the nutrient group known as the branched-chain amino acids. But this essential amino also performs on its own to help decrease muscle breakdown, boost muscle mass and fat loss, and promote recovery.
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Leucine is a powerful part of the nutrient group known as the branched-chain amino acids. But this essential amino also performs on its own to help decrease muscle breakdown, boost muscle mass and fat loss, and promote recovery.
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Gavin Rossdale and Bush. Rob Halford and Judas Priest. Nigel Tufnel and Spinal Tap. There are quite a few examples of solo acts that really were better left as part of an ensemble. On the flip side, there are the solo acts that are so good, the former groups are forgotten, such as Peter Frampton and Humble Pie. (Was there really a band called Humble Pie?) Then there are the stellar acts that are good no matter who they’re with — think Sting and The Police or Paul McCartney and The Beatles.

Like Sting and McCartney, leucine is notable as a solo performer and as a member of a group, the branched-chain amino acids. The three BCAAs — leucine, isoleucine and valine — are like-structured amino acids that the body uses for metabolic processes, the most notable of which is muscle protein synthesis. In fact, the BCAAs make up about one-third of muscle protein. Because they are essential amino acids, the BCAAs have to be consumed through dietary protein sources like meat, beans and dairy, as well as dietary supplements, because the body cannot manufacture these nutrients like it does the nonessential amino acids.

Supplementally, research shows that leucine on its own and combined with the other BCAAs is helpful for improving muscle synthesis, decreasing muscle breakdown and fat mass, and promoting recovery.

Preserving Protein

Leucine, otherwise known as L-leucine, has been a popular study subject because of its ability to hamper muscle degradation. In fact, researchers have been particularly focused on studying leucine supplements in the elderly because of the typical short-circuiting that causes declines in lean mass during aging. Leucine supplements have been shown to inhibit the process known as muscle proteolysis — when the body’s enzymes preferentially break down and metabolize muscle proteins for energy — as well as increase muscle protein synthesis in the elderly.

In athletes, leucine has proved to be multifunctional. One research review published in 1999 cited several of leucine’s benefits, including the fact that taking a BCAA supplement with 30 percent to 35 percent leucine before or during endurance exercise can inhibit exercise-induced protein breakdown, as well as help maintain the body’s glycogen (or carb energy) stores. Like the body’s glycogen reserves, leucine levels are depleted during strenuous exercise, but taking a leucine supplement can stymie this drop. Power-trained athletes in one study took 50 milligrams per kilogram of bodyweight of leucine per day for five weeks, which effectively prevented the distinctive drop in serum leucine levels.

A team of researchers in the Netherlands reported in 2005 that adding leucine to a carb-protein supplement stimulates muscle protein synthesis and optimizes whole-body protein balance compared to a carb-only supplement. Specifically, the added leucine reduced athletes’ protein oxidation, lowered whole-body protein breakdown and increased whole-body protein synthesis and muscle growth.

The Lighter Side

Leucine not only affects protein metabolism and synthesis but also has a slimming effect and is known to help reduce fat. Although there is some argument about whether leucine can be used as a weight-loss supplement, research cited in a 1999 review showed that dieters who moderately restricted their calorie intake and took a BCAA supplement containing 76 percent leucine lost weight. The researchers noted that leucine helps the body preferentially burn fat for energy.

Leucine also helps maintain muscle mass during dieting, according to a 2003 report in The Journal of Nutrition. Researchers studying leucine’s role in weight-loss diets reported that leucine, either on its own or as part of a meal, helps maintain muscle mass because it increases plasma and intracellular levels of leucine. In their studies, the researchers showed that combining a moderate diet that includes 10 grams per day of leucine with exercise promoted significantly more weight loss in study participants than those who strictly followed recommended daily allowances for fat, carb and protein intake. The participants in the treatment group also lost more fat and maintained more muscle mass during the 16-week study than the people in the control group.

It’s a Hit

Consuming more than just the recommended levels of leucine and the BCAAs also may thwart muscle protein breakdown during exercise, according to one Australian study. For the two-week trial, 16 men either maintained their normal diets or added 12 grams per day of BCAAs to their regular regimen. Base-line tests showed that all the men were getting the recommended amounts of BCAAs as part of their normal diets and that they all had similar post-exercise levels of serum creatine kinase (CK) and lactate dehydrogenase (LDH) — intramuscular enzymes that indicate muscle breakdown. After seven days, the researchers administered an endurance test, took blood samples, and learned that the men taking the BCAA supplement had lower levels of CK and LDH than the men in the control group, suggesting BCAA supplements reduced muscle damage sustained during exercise.

As a part of exercise-induced muscle protein breakdown, leucine and BCAA metabolism increases. Researchers believe, however, that leucine is the amino most affected by exercise. Studies show that leucine acts synergistically with insulin in certain intracellular pathways to stimulate protein synthesis, which makes a post-exercise meal an absolute must for promoting recovery and stimulating muscle growth. Taking amino acids after exercise helps elevate leucine back to beneficial levels and stimulates insulin release, which together allows for muscle growth.

Whether you take leucine on its own or in concert with the other BCAAs, it is clear that for a harmonious muscle state, post-exercise leucine is a total rock star.


HMB — which stands for beta-hydroxy-beta-methylbutyrate — is a leucine metabolite that can be taken supplementally to help promote size and strength gains by preventing muscle breakdown during exercise. One study showed that taking 3 grams per day of HMB during a four-week resistance-training program effectively increased upper-body strength and minimized muscle damage in men and women whether they had training experience or not.

Another study compared HMB to creatine and showed that the two work differently but have additive effects. During a three-week trial, subjects took 3 grams per day of HMB, 20 grams per day of creatine for one week and then 10 grams per day for the following two weeks, a combination of HMB and creatine, or a placebo. Participants gained lean mass and strength in the three treatment groups compared to the placebo, and the group taking HMB had less protein breakdown. This effect was even more pronounced in the HMB-plus-creatine group, suggesting the two may make a good team.