Leucine is one of the three essential amino acids. Because of their structure, leucine, along with isoleucine and valine are called branched-chain amino acids (BCAAs). Leucine increases muscle mass and help with muscle recovery after exercise, that’s why leucine supplements are very popular among bodybuilders and athletes. Leucine is sometimes referred to as the main amino acid because it is primarily responsible for the muscle building benefit of the BCAAs. Leucine also regulates blood sugar and provides energy for the body. Leucine is highly effective for stimulating skeletal muscle protein synthesis (MPS).

Leucine is an essential amino acid, meaning our body cannot produce it so we have to get it from diet or supplements.


What are branched-chain amino acids (BCAAs)?

BCAAs are essential nutrients that our body obtains from proteins in diet, especially meat, legumes and dairy products. There are 3 branched chain amino acids in our body – leucine, isoleucine, and valine. About a third of our muscle protein is made up of BCAAs. They are called branched-chain because of their chemical structure. People use BCAAs for medicine. They are used to treat amyotrophic lateral sclerosis (also known as ALS or Lou Gehrig's disease); brain disorders arising from liver disease, known as hepatic encephalopathy; tardive dyskinesia – a movement disorder; genetic disease called McArdle's disease; and poor appetite in cancer patients and elderly kidney failure patients. Branched-chain amino acids are also used in people who are confined to bed as it helps slow muscle waste.

Some people use BCAAs to improve concentration and prevent fatigue.

BCAAs are athletes’ favorite who use them to boost exercise performance and lower protein and muscle breakdown during intense workout.

Healthcare providers administer BCAAs intravenously to patients with acute hepatic encephalopathy (sudden brain swelling due to liver disease) and also when the body experiences maximum stress, for example after widespread infection or serious injury.


What Does Leucine Do for the Body?

Leucine supports the body in the following ways:

  • Urges weight loss
  • Activates mTOR. mTOR is a protein synthesis regulator. It responds to leucine, and it is crucial for skeletal muscle hypertrophy.
  • Promotes muscle development and growth
  • Provides cholesterol and blood sugar control
  • Stimulates insulin release


Improves performance

A randomized, double blind study examined the effect of leucine supplements on a number of physical and performance attributes in canoeists. Participants were either given 45 mg of leucine per kg bodyweight or 45 mg of corn flour placebo per kg bodyweight for 6 weeks. The participants’ dietary intakes were kept almost similar throughout the trial.

The results showed that the participants receiving leucine supplements had enhanced upper body power, decreased rate of perceived exhaustion and extended period of exercise time before becoming fatigued.


Produces lean muscle mass

A rat model study examined the effect of leucine in building lean muscle mass. The researchers increased the rodents’ leucine intake by 50 percent and also reduced their food intake by 50 percent for 6 weeks. The results showed that the rats receiving leucine supplements had a remarkably greater percentage of lean body mass preserved.


Drives weight loss

Several studies have shown that leucine can help people speed up their weight loss and gain extra muscle while on a diet.

Researchers from the University of Illinois recently assessed weight loss diets that contained 10 grams of leucine combined with 125 grams of protein daily, with at least 2.5 grams of leucine during each meal.

The researchers found the participants that consumed diets high in leucine experienced:

  • Greater weight loss
  • Substantial fat loss
  • Better lean body mass preservation
  • Enhanced glucose control


A Columbia University study analyzed rats that were fed high-fat diets. Results showed that the rats who received leucine supplements had their fat weight reduced by 25%. The researchers also found that leucine promoted better control of blood sugar, leading to a decrease in total cholesterol and LDL cholesterol (“bad” cholesterol). Leucine also helped the rodents increase their uncoupling protein 3 (UCP3) levels, which often causes the body to lose energy instead of reserving it as body fat.


Promotes muscle growth and development

Leucine increases the rate of skeletal muscle protein synthesis (MPS) faster than other amino acids. Consequently, it fosters exceptional muscle growth and development.

A recent study on animal models analyzed MPS. The researchers provided the animals with various amino acids. The researchers assessed the results in combination with glucose ingestion.

In the first stage, the animals were given a protein supplement that had all the amino acids. In this stage, the results revealed a spike in MPS levels.

Next, the animals were given EAAS and BCAAS, respectively. The results showed that the animals’ MPS levels increased at the same rate. In the final stage, the animals were provided with leucine only, and the result showed the animals’ MPS increased at the same rate.


Regulates cholesterol and blood sugar

Leucine may be helpful for regulating cholesterol levels as well. A 2009 study on rats showed that the rodents that received leucine supplements showed increased levels of HDL cholesterol (“good” cholesterol) in their blood.

Additionally, our body needs glucose for energy. Although many amino acids supply glucose, only leucine can replace glucose during fasting.

During intense workout, a person may be unable to use muscle for energy due to an increased glucose level. On the other hand, studies have shown leucine to be more effective at helping to regulate blood sugar levels than the other two BCAAs isoleucine and valine. Both these amino acids convert glucose at slower pace than leucine.


Stimulates insulin release

Leucine supplements may trigger insulin release, ensuring key nutrients can consistently reach the muscle cells.


What are the best natural sources of leucine?

Below is a list of foods highest in leucine content:

Parmesan cheese: 100 g provides 3452 mg or 126% of Recommended Dietary Allowance (RDI). Other cheeses high in leucine: Gruyere, Romano, Swiss, Fontina, Hard Goat’s Cheese, Edam, Gouda.

Soybeans (Roasted): 1 cup (93 g) provides 2997 mg or 110% of RDI. Other soy foods high in leucine: Natto, Soy flour, Tempeh, Soybeans, Miso, Firm tofu.

Beef (Sirloin, grilled): 100 g provides 3165 mg or 116% of RDI. Other Red Meats High in Leucine: Lean Steak, Beef Rib Eye, Veal Leg, Lamb Shoulder, Venison, Veal Sirloin, and Stewing Lamb.

Chicken (Breast, cooked): Breast piece (180 g) provides 4800 mg or 176% of RDI. Other Poultry High in Leucine: Fat Free Ground Turkey, Turkey Wings, Chicken Stewing Meat, Turkey Breast, Turkey Drumsticks, Chicken Wings & Chicken Drumsticks.

Pork (Sirloin, cooked): 100 g provides 2560 mg or 94% of RDI. Other Pork Cuts High in Leucine: Ground Pork & Pork Chops, Pork Tenderloin, Ham, and Spareribs.

Seeds & Nuts (Pumpkin Seeds): 100 g provides 2419 mg or 89% of RDI. Other Seeds & Nuts High in Leucine: Sunflower Seeds, Pistachio Nuts, Sesame Seeds & Almonds, Chia Seeds, Flaxseeds & Cashew Nuts, and Brazil Nuts.

Fish (Tuna, cooked): 100 g provides 2293 mg or 84% of RDI. Other Fish High in Leucine: Wild Salmon, Trout & Snapper, Mackerel, Salmon, Halibut & Tilapia, and Pollock.

Seafood (Octopus, cooked): 100 g provides 2099 mg or 77% of RDI. Other Seafood High in Leucine: Lobster, Shrimp, Crab, Clams, Mussels, and Crayfish.

Peanuts: 100 g provides 1812 mg or 66% of RDI. Peanut Butter (both smooth and chunky) is also high in Leucine.

Beans (White, cooked): 100 g provides 776mg or 28% of RDI. Other Beans High in Leucine: Cranberry, Pinto & Kidney Beans, Yellow Beans, Navy Beans & Small White Beans, Pink Beans & Black Beans.



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