The Essential Amino Acids - Part 1: Arginine, Histidine, Isoleucine, Leucine and Lysine

The essential amino acids covered in this part of the article are: arginine, histidine, isoleucine, leucine and lysine. In total there are 10 essential amino acids; this is because arginine is only needed in children and not adults, for this article we will be focussing on 4 of the essential amino acids in adults. These amino acids are essential as they cannot be created by the body, they can only be produced from the food we eat. Interestingly, one of the non-essential amino acids tyrosine is produced from the essential amino acid phenylalanine, so phenylalanine deficiency will result in tyrosine deficiency also.

Starting with histidine, this is generally produced by the body in adults, children may not hence it is coined a ‘semi-professional’ amino acid. It is particularly important in the myelin sheath that coats nervous cells which transmit messages to the brain. Histidine is also used to make histamine, the reason you swell and itch when you have an allergic reaction. In the muscle, histidine is resynthesized back into Carosine (alongside beta-alanine) by the enzyme Carosine synthase. Increasing histidine is linked to increased muscle Carosine concentrations- research has also found low histidine levels leads to lower Carosine levels. As a general guide, practitioners recommend 8-10 milligrams per kilogram of body weight daily, for muscle growth, 3 grams a day is a figure regularly suggested but this would be the upper end of the histidine daily intake scale. Foods high in histidine include: wheat, rye, yellow fin tuna, mackerel, chicken, beans, eggs, cauliflower and citrus fruits to name a few.

Isoleucine is one of the three branched chain amino acids (BCAA) that you always read about on the back of any good protein powder. It also has branched hydrocarbon side chains and can be interchangeable with leucine and valine (the other two BCAA’s) in proteins. These along with the other two BCAA’s promote muscle recovery after exercise as well as regulating blood sugar levels. Isoleucine biosynthesis is very complex but one of the final steps involves valine aminotransferase transferring an amino group from glutamate to produce isoleucine. It is important to remember that it can only be synthesised in plants and bacteria and the final product is used in the human diet- it cannot be synthesised by humans! Its usage post-exercise is because it maintains proteins balance to promote muscle growth and healing. It also prevents muscle breakdown and healing of the tissues after trauma i.e. a strenuous weight session. A recommended supplementation of isoleucine would be between 10-12 mg per kg of body weight daily. Foods high in isoleucine include: eggs, sausage, bacon, parmesan cheese, cod, almonds and cashew nuts.

In order to produce a positive post workout protein balance, leucine must be consumed, it will remain negative otherwise. As mentioned earlier, leucine is one of the BCAA’s, however it is considered the most important BCAA as it roughly has 10 times greater impact on protein synthesis than any other amino acid. The anabolic pathway mammalian target of rapamycin (mTOR) is activated by leucine and a decrease in leucine signals to mTOR that there is not enough protein to synthesize skeletal muscle- and as a result mTOR is deactivated. Some studies have shown 2.5 grams is enough to stimulate protein synthesis whereas others have shown as much as 8 grams are needed and in athletes up to 20 grams has been suggested. It all depends on the individual but more importantly the timing i.e. it may be 20 grams but not in one sitting- take it throughout the day. The best food sources of leucine include any proteins from animals. The protein source with the highest leucine content is whey. Whey contains roughly 10% leucine whereas casein slightly less, weighing in at 8%.

Fatty acids can be converted into energy and cholesterol can be lowered both made possible by carnitine- lysine is essential in the production of the compound. As well as this, lysine helps the body absorb calcium and decrease the amount of calcium lost in urine. Because of this, lysine is linked to helping bone loss associated with osteoporosis. Lysine is also important in the role of collagen which is very important for connective tissues including skin, tendon and cartilage, not many people realise that collagen is the most abundant protein in our bodies. Lysine also maintains nitrogen levels, essential because nitrogen is essential in muscle growth and if the body is excreting more nitrogen than is being used up, a warning signal is sent out that one should increase their protein intake immediately. Nitrogen excretion can be measured to determine how much protein is present in the body. The daily dosage of lysine is about 12 mg per kilogram of body weight per day. Sources of lysine include meat (specifically red meat, pork and poultry) nuts, eggs and soy beans.