What is Leucine?
Leucine is an essential amino acid as the body cannot synthesise it and needs to be obtained from the diet. Leucine is one of the three branch chained amino acids (BCAAs). The two other BCAAs are Isoleucine and valine.
BCAAs are needed in the synthesis of excitatory or inhibitory neurotransmitters which includes GABA.
Health Benefits of Leucine
Helps build muscles
Leucine is an essential amino acid and is a part of the branched-chain amino acid (BCAA) group. It is needed for building muscle mass. BCAAs are a common supplement taken by athletes and body builders.
Leucine is important for muscle growth, repair and recovery but much of its benefits for muscle maintenance comes from working synergistically with the other BCAAs isoleucine and valine. It is found to be low in athletes and body builders which is why BCAAs are a popular supplement for sports.
The body needs BCAAs for muscle repair and growth.
BCAAs may also be useful for women to ingest around the mid luteal phase due to increased protein breakdown. The mid luteal phase is around cycle days 18 – 23.
Like valine, leucine is also important for muscle growth and prevents muscle breakdown.
Protein and BCAA supplementation have shown to increase muscle strength and muscle mass in elderly people with a condition known as Sarcopenia. Sarcopenia is characterized by a loss of skeletal muscle mass, deterioration of muscle fat and a loss of muscle strength which occurs with aging. This condition can make people frail and at higher risk of injury. [R]
Helps with neurotransmitters
BCAAs are involved in the synthesis of excitatory or inhibitory neurotransmitters needed for cognitive function and depends on the genetic disposition of the person. Valine supports the central nervous system and cognitive function.
BCAAs are needed for the production of excitatory neurotransmitter glutamate and inhibitory neurotransmitter gamma-aminobutyric acid (GABA) within the brain due to the role of these amino acids as nitrogen donors.
[R]BCAAs are also important for glutamate metabolism.
Supports weightloss
Studies have shown leucine can help with weight loss as it suppresses appetite and by burning visceral fat deposits. This can help with leaner body mass with increased muscle growth which makes it an ideal supplement for athletes and body builders.
BCAA has shown to reduce or burn visceral body fat. This type of fat is deposited around the organs which is harmful and can lead to various chronic diseases such as heart disease, diabetes and cancer. This type of fat can be difficult to remove.
Studies have shown that BCAA can help lose weight and weight from visceral adipose tissue. [R] [R]
Reduce stress and anxiety
Studies have shown BCAAs intake reduced the odds of depression and anxiety. A higher intake of valine, leucine and isoleucine is also linked to reduced odds of depression and anxiety. [R]
BCAAs are a source of nitrogen which needed in the synthesis of proteins required by skin, hair, nails, blood and muscles. BCAAs are especially important in times of stress by helping to supply more energy.
Regulates blood sugar levels
BCAAs are not only important for tissue repair and muscle growth but needed to help regulate blood sugar levels to sustain energy levels.
Leucine is involved in regulating blood sugar levels and may prevent diabetes. Leucine can improve glucose homeostasis and may help control blood sugar.
Multiple studies on animals have shown that increasing leucine intake can help reduce obesity caused from poor diet, hyperglycemia, and cholesterol levels.
More studies are being done in order to determine the role leucine plays in people with diabetes.
Diabetes complications can lead to muscle wasting which sees a rapid breakdown of muscle mass for which it is suggested that leucine may help. The BCAAs play an important role in preventing breakdown of muscle which may be helpful for people with insulin dependent diabetes.
Leucine along with the other BCAAs can improve protein synthesis. In insulin dependent diabetes intake of BCAAs which includes leucine can promote protein synthesis and prevent protein breakdown.
Supports recovery from injury
BCAAs can help support recovery from injury. Leucine has in important role in the health of skin, bones and muscle health. It supports muscle growth and a lean body mass. It can also support the production of human growth hormone (HGH). Leucine is involved in muscle tissue repair and can support health of skin and bones following traumatic injury. BCAAs have shown to support the sleep wake cycle of people following traumatic brain injury which is more likely because sleep is greatly involved in healing.
BCAA supplements are usually recommended to support health post-surgery as it can support recovery thereby speeding up the healing process.
Agonist / Synergist
Vitamins B7, B12
Amino acids BCAAs
Leucine works synergistically with isoleucine and valine for muscle growth and development and for many of the other health benefits
BCAAs are catalyzed by propionyl-CoA carboxylase which is an enzyme that requires biotin (vitamin B7) for its functions.
Biotin (vitamin B7) is an essential cofactor for carboxylase enzymes. These enzymes are involved in the metabolism of fatty acids and amino acids
Carboxylase enzymes are essential for the utilisation of BCAAs for neurotransmitters synthesis and to produce energy
BCAAs are nitrogen donors and help with synthesis of inhibitory neurotransmitter glutamate and inhibitory neurotransmitter gamma-aminobutyric acid (GABA)
Coenzyme-forms of cobalamin assist with the degradation leucine. These enzymes are also needed for the degradation of propionic acid and the re-methylation of homocysteine to methionine
Vitamin B12 is needed for coenzyme-forms of cobalamin
Antagonists
Amino acids Phenylalanine, tryptophan
BCAAs (branched chain amino acids includes leucine, isoleucine and valine) compete with phenylalanine and tyrosine which can impact levels of neurotransmitters found in the brain that follow the catecholamines pathway which include dopamine, epinephrine and norepinephrine.
BCAAs compete for transport across the blood-brain barrier (BBB) with tryptophan and can impact serotonin levels
Elevated blood levels of BCAA deplete tryptophan in the brain, which causes low serotonin
BCAAs compete with phenylalanine and tyrosine for transport across the blood-brain barrier [R]
Ceruloplasmin, a copper binding protein can inhibit leucine uptake. [R]
Ceruloplasmin is an important copper binding protein, also known as a multicopper ferroxidase, it is made in the liver and helps histamine breakdown with the help of the copper containing enzyme histaminase. Ceruloplasmin helps with copper storage and transportation from the liver into the bloodstream carrying it to parts of the body where it is needed.
Ceruloplasmin regulates copper and is also involved in homeostasis of both iron and copper.
Food Sources of Leucine
Amino acids are found in abundance in animal food sources.
Leucine can be found in a variety of foods. Animal food sources of this amino acid include beef, chicken pork, tuna, and yoghurt.
Plant based food sources of leucine include lentils, soy protein, tofu, navy beans, podded peas peanuts, sesame seeds, pumpkin seeds, oatmeal, mushrooms, leafy greens and squash.
Recommended Daily Allowance
Adults need around 39mg to 42mg per kg of body weight per day from dietary intake for optimal functioning.
Children need more amino acids that adults as their body is still developing. The recommended daily amount for children over the age of three increases by 10% to 20% more than what is needed by adults. For infants the amount required increases by 150% more than what is needed by adults.
The requirements may change on individual basis and highly dependent on existing health.
Leucine Supplementation
Leucine is available as capsules, tablets or powders. This amino acid can be found in many full spectrum amino acid supplement. Leucine is not widely available as a single supplement and is found in supplements providing all three BCAAs which includes valine and isoleucine. BCAA supplements are often advertised as a sports supplement as they are beneficial for athletes and body builders.
Taking leucine in a BCAA supplement is more convenient than taking it as a singular amino acid as all three BCAA work synergistically for the health benefits and functions of the body.
BCAAs as powdered supplement do not taste good and are commonly found with added flavour. For this reason it is better to take capsule or tablet forms.
Only recommended dosage should be taken which may be found on supplement label or if in doubt ask a health professional. Excessive or high amounts of BCAA should be avoided.
BCAAs have to be taken in the correct ratio for better absorption and to achieve the health benefits from these amino acids. The recommended ratio is 2:1:1 which would equate to about 2 mg of leucine and 1mg each of isoleucine and valine. Most BCAA supplements are available in the correct ratio but various other ratios are also available and may require some experimentation. Another reason for this ratio is because it has shown to be most effective for stamina and endurance.
BCAA supplements can be taken at any time which includes before, during, or after exercise and at any other times. They can also be taken at bedtime however it is best to take at least an hour before bed.
BCAAs taken at bedtime may help with the synthesis of muscle protein over the period of sleep, however this has not been studied.
Taking single amino acid supplements are not always recommended and may be harmful for those with damaged liver or kidneys.
Deficiency Symptoms of Leucine
Leucine deficiency is uncommon because BCAAs are readily available in a variety of foods. Deficiency is likely from excessive exercise and without replenishing BCAA levels either through diet or appropriate supplementation.
Signs and symptoms of leucine deficiency include;
- Dizziness
- Headaches
- Depression
- Confusion
- Fatigue
- Irritability
Causes of low leucine include:
- Inadequate dietary intake (low protein diets)
- Excessive or strenuous exercise (as seen in athletes and body builders)*
*Athletes and body builders and people who generally exercise a lot to build muscle mass have an increased need for leucine and the other BCAAs. BCAAs are a popular sports supplement.
Most people may not require supplementation of BCAAs if following a healthy diet however a severe deficiency will require supplementation. If a deficiency is suspected it is important to check levels with a health professional such as a doctor. [R]
Toxicity Symptoms of Leucine
Leucine is an essential amino acid, however excessive amounts can cause a host of symptoms. The signs and symptoms of excess leucine include:
- Branched-chain ketoaciduria also called maple syrup urine disease (MSUD)*
- Exacerbates pellagra symptoms (competes with tryptophan and inhibiting the conversion of tryptophan to niacin which can make these symptoms worse in those who are already low on niacin)
- Offensive bodily odor (including breath)
- Reduced levels of serotonin – competes with serotonin precursor tryptophan
- Reduced levels of dopamine – competes with dopamine precursor phenylalanine and tyrosine
- Impaired kidney function
- Impaired liver function
- High levels of toxic ammonia in the body
- Disturbance in the sleep-wake cycle in healthy individuals
BCAAs have been shown to be effective in the sleep-wake cycle in people suffering from traumatic brain cycle however it is not as beneficial in high amounts in healthy individuals and instead may cause a disturbance in the sleep-wake cycle.
It is not recommended to take BCAAs with impaired liver or kidney function and a person’s health will need to be assessed before considering therapy with BCAAs.
Excess leucine impacts the metabolism of tryptophan to niacin. Niacin deficiency is linked to a condition called pellagra. [R]
Toxicity causes of leucine:
- Excessive supplementation of leucine
- Branched-chain ketoaciduria – impaired metabolism of BCAAs
- Vitamin B7 deficiency
Biotin (vitamin B7) is an essential cofactor for carboxylase enzymes. These enzymes are involved in the metabolism of fatty acids and amino acids which includes BCAAs.
Carboxylase enzymes are essential for BCAA metabolism for neurotransmitter production and energy. Deficiency of vitamin B7 can impair the functions of these enzymes. A deficiency of vitamin B7 is linked to cognitive decline, mood changes, depression, fatigue, hallucinations, and numbness and tingling of the extremities.
Toxicity is treated by restricting dietary intake of leucine.
BCAAs “steal” tryptophan and compete with uptake in the brain which can lower serotonin levels. Low serotonin levels affects mood and may be a cause for low mood or depression. Serotonin also regulates appetite and when significantly reduced can cause binge eating especially of simple carbohydrates.
Studies have shown that low serotonin level from high BCAA intake in mice fed with twice as much as the normal amount resulted in the animals becoming obese from overeating. Obesity significantly increases poor health conditions and reduces lifespan. [R]
Excess BCAAs may cause the production of too much insulin which can lead to low blood sugar levels (hypoglycaemia) if glucose reserves are rapidly used up or not being replenished through the diet.
Branched-chain ketoaciduria is a metabolic disease characterized by impaired metabolism of BCAAs. It is also known as maple syrup urine disease (MSUD) as the odour from the urine is similar to maple syrup. Although this condition does not indicate low levels of BCAA it is a sign that the BCAAs are not being utilized by the body which will lead to toxic levels of BCAAs. This condition can cause delirium and neurological problems.Amino acids are transported to the liver during digestion where protein is synthesised.
If there is too much protein the amino acids can convert into fat and stored in fat deposits or if needed made into glucose for energy by gluconeogenesis.
Excess amino acids from protein digestion can be excreted safely. The amino acids are deaminated in the liver where they are formed into ammonia which can be toxic if not eliminated. In healthy liver functioning the ammonia is converted to urea for safe excretion. [https://pubmed.ncbi.nlm.nih.gov/103372/]
Excess amino acids are excreted by the liver through liver cells releasing urea and water which are transported to the kidneys to filter the blood and then excreting urea through urine.
It is important to seek medical advice from medical practitioners such as a General Physician before taking any BCAA supplements as certain conditions such as an impaired kidney or liver function can worsen.