While each of the 22 or so amino acids commonly found in our diet is valuable in its own way, leucine is arguably the most important. Leucine is one the branched chain amino acids, or BCAAs, and is essential because we cannot synthesize this molecule in our bodies; it must be obtained through foods or supplementation.
Leucine is found in all protein containing foods, but at very varying concentrations and differing levels of availability. Proteins that are considered to have high biological values (BV) are very rich in leucine AND highly digestible. Lesser quality proteins with lower concentrations of leucine and/or containing other components that interfere with leucine absorption must be consumed in larger quantities to provide sufficient amounts for optimized muscle development and performance.
What makes leucine so important? Leucine appears to have a greater stimulatory effect on muscle protein synthesis than any other amino acid. At the same time, this particular BCAA seems to decrease existing muscle protein breakdown. Moreover, the activating and protective benefits have been observed to occur independently of other essential amino acids (EAAs), leading scientists to believe that leucine is largely responsible for the anabolic and anticatibolic benefits of consuming a high protein diet.
As an avid lifter, the benefits of anything that helps facilitate new muscle building while protecting the muscle that you’ve worked so hard to amass is pretty obvious – particularly when you consider the safety, legality, and availability of the compound in question. But leucine may play equally important health roles by preserving lean muscle mass in the elderly and facilitating better blood sugar control and weight-loss in obese populations.
Good sources of leucine include (approximates per 100 g portion): native whey protein isolate (13 g), whey protein concentrate (9 g), dried egg whites (6.8 g), soy protein isolate (6.8 g), nonfat dry milk (3.5 g), soybeans (3.3 g), lean beef (3.2 g), chicken breast (2.6 g), turkey breast (2.6 g), lean pork (2.5 g), reduced fat cheese (2.4 g), anchovy (2.3 g), canned tuna (2.3 g), cottage cheese (1.2 g), whole egg (1.1 g), Greek yogurt (0.5 g), Nonfat milk (0.3 g)
How much leucine you need depends on factors like your age, how active you are, your personal goals (strength, endurance, overall muscle accumulation, general health, etc.), but a 2-5 gram (2,000-5,000 mg) dose, taken several times throughout the day, seems to be effective for most. If you’re dieting, consider taking greater amounts more frequently to minimize loss of lean mass.
A typical protein shake containing 24 grams of protein, ¾ cup of canned tuna, 6 oz chicken breast, 5 oz of lean beef, and a serving of 2:1:1 BCAA powder each deliver about 2.5 grams of leucine. Spreading your leucine intake out (e.g., 5 g leucine taken 4-5 times daily) is more effective than taking 20 g twice a day. Also, make sure that you are getting enough total protein to ensure that your body has access to the building blocks needed for muscle accretion signaled by increased leucine ingestion.