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Losing Fat with Leucine

By John Parrillo

Leucine is one of three branched-chain amino acids (isoleucine and valine are the other two BCAAs). Leucine, which comprises about one-third of muscle protein, plays multiple roles in metabolism. It enters muscle cells and turns on key biochemical processes that result in more muscle protein and, thus, more muscle development and greater fat-burning. It also functions as a fuel for skeletal muscle and stimulates the recovery of muscle protein synthesis after exercise.

Leucine is involved in the production of the amino acids, alanine and glutamine, in skeletal muscle. During and following exercise, large quantities of alanine and glutamine are released from muscle. They then travel through the bloodstream to the liver, where they can be used to manufacture glucose and glycogen. The loss of alanine and glutamine caused by exercise is over and above the amount available in muscle. Leucine to the rescue. It donates nitrogen to build and replenish alanine and glutamine.

What’s more, leucine increases the secretion of the anabolic hormone insulin, important for encouraging growth. Therefore, this essential amino acid is not only a building block, but it is also needed to turn on your muscle-building and fat-burning processes. It is one of the reasons high-protein diets work so well for maintaining lean muscle mass and losing body fat.

I’m focusing mostly on leucine in this column, because it is is the most important of the BCAA trio. This is because leucine acts like an ignition key that turns on the protein-building process. Isoleucine and valine provide the building blocks required once that process gets underway.

The Scientific Case for Leucine

Leucine has remained in the scientific spotlight lately for its positive effect on body composition. Researchers at the University of Tennessee in Knoxville demonstrated that leucine exhibits a synergy with B6, resulting in reduced body fat storage coupled with increased fat burning. Specifically, 2.25 grams leucine and 30 milligrams of B6 increased fat burning significantly, and the subjects didn’t even have to cut calories. The researchers concluded: “This nutraceutical combination results in significant fat loss in the absence of caloric restriction and markedly enhances weight and fat loss by 50%-80% over a 24-week period.”(1)

In 2016, researchers in Denmark studied men and women, ages 35 to 65, for six years to determine how well leucine intake helped preserve lean muscle tissue. They discovered that the higher the leucine intake (approximately 7 grams daily) the better the subjects maintained their lean mass. This was particularly evident in the older subjects, hinting that leucine has a pretty powerful anti-aging effect. (2)

As for BCAAs taken together, researchers at the College of Charleston, Charleston, South Carolina, and Ball State University, Muncie, Indiana, looked into whether short-term amino acid supplementation could maintain a short-term net anabolic hormonal profile and decrease muscle cell damage during a period of high-intensity resistance training, thereby enhancing recovery and decreasing the risk of injury and illness.

Eight previously resistance trained males were randomly assigned to either a high branched chain amino acids (BCAA) or placebo group. Subjects took the supplement for three weeks before beginning a fourth week of supplementation along with high-intensity total-body resistance training. Blood was drawn prior to and after supplementation, then again after two and four days of training. Serum was analyzed for testosterone, cortisol, and creatine kinase (a muscle enzyme that, when elevated, indicates muscle breakdown). Serum testosterone levels were significantly higher and cortisol and creatine kinase levels were significantly lower in the BCAA group during and following resistance training. These findings suggest that short-term BCAA supplementation may produce a net anabolic hormonal profile while easing training-induced increases in muscle tissue damage. So it makes sense that supplementing with BCAAs might help prevent muscle loss, and even help build it. (3)

Many other studies demonstrate that eating more high quality protein will increase the amount of leucine in the diet, helping you maintain muscle mass and burn body fat during weight loss. Maintaining muscle during weight loss efforts is essential because it helps the body burn more calories.

Sources of Leucine

While the body makes many other amino acids, it does not produce leucine, so we need to consume foods rich in it. Leucine is found primarily in high quality protein foods such as beef, poultry, fish and eggs.

leucine-muscle-amino-optimized-wheyAnother terrific source of leucine is through supplemental protein beverages. Of the commonly available dietary proteins, whey and casein have the highest leucine contents (14 percent and 10 percent, respectively, of their total protein content). Whey, in Parrillo’s Optimized Whey™ Protein, would be ideal. As a fast-digesting protein, it can move leucine to the muscles as quickly as possible. Place two scoops in a small plastic container, throw the dry mixture in your gym bag, office desk drawer, or purse and mix with 8 ounces of water.

BCAAs, including leucine, are found in our Muscle Amino Formula. All three work synergistically with each other. The time to use this product is immediately before and after training. Hard dieting is also a great time to supplement with it. During times of energy insufficiency (dieting), your body will actually break down its own muscle to use as fuel if no other is available.

Catabolism is a dreadful metabolic state that occurs when glycogen stores have been depleted and fat oxidation has maximized. Metabolically, your body requires a certain level of glucose (blood sugar) to be maintained in order for the brain to function. While body fat provides a long-lasting energy supply, fat cannot be converted into glucose by the human body. But protein (amino acids) can. Under adverse conditions, carbohydrates are exhausted and your body breaks down protein stores (muscle tissue) to convert into glucose to supply energy. Branched chain amino acids are effective because they form a substrate for growth and are metabolized as fuel directly within muscle cells.

A handful of Muscle Amino Formula™ capsules will help prevent the onset of catabolism and has both anabolic and anti-catabolic properties. We suggest two or more with every meal. Remember that BCAAs require insulin for absorption into muscle cells so take them with food (carbs) rather than on an empty stomach!

With these supplements, along with the protein-rich Parrillo Nutrition Program, there has rarely been a quicker or more effect way to make sure you get all the benefits of protein, especially leucine.


  1. Zemel, M.B., and Bruckbauer, A., 2013. Effects of a leucine and pyridoxine-containing nutraceutical on body weight and composition in obese subjects. Diabetes, Metabolic Syndrome, and Obesity 6: 309-315.
  2. McDonald, C.K., et al. 2016. Lean body mass change over 6 years is associated with dietary leucine intake in an older Danish population. British Journal of Nutrition 115: 1556-1562.
  3. Sharp, C.P., and D.R. Pearson. 2010. Amino acid supplements and recovery from high-intensity resistance training. Journal of Strength and Conditioning Research, March 17.


2018-11-09T17:00:35-04:00 November 9th, 2018|by John Parrillo|

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