It’s a fact of fitness: Protein is a critical nutrient for building lean mass. Anyone who knows that probably also knows that protein is made up of amino acids and that different protein sources have different ratios of aminos. Soy protein, for example, is high in arginine, while whey is high in branched-chain amino acids.
While we would never recommend that you stop getting your aminos from whole-food protein sources or protein powders, taking aminos as individual supplements can also be enormously beneficial. This A–Z rundown of the functions of each of the 20 proteinogenic (or protein-building) amino acids in the human body will show you why.
Nonessential Amino Acids
It’s a common mistake — all these aminos are actually essential, as in required by the body, but they’re called “nonessential” because the body can make them on its own. Still, supplementing with many nonessential aminos can be beneficial because it ensures that the body gets sufficient levels to maximize their benefits.
Alanine is involved in energy production, but its cousin, beta-alanine, is much better known and much more powerful. When combined with histidine (see below), beta-alanine creates carnosine, which is proving to be quite the muscle-molder. Studies on beta-alanine have shown that it can increase muscle growth, strength and power and encourage fat burning.
Asparagine was derived from asparagus juice (hence its name), and it’s also responsible for the, um, distinctive odor of your urine after you’ve eaten asparagus. That’s not all it does, though. Asparagine is required by the liver (to synthesize other amino acids) and the nervous system.
Aspartic Acid may be a nonessential amino, but without it, there would be no methionine, threonine, isoleucine or lysine. Besides helping create those aminos, it is involved in energy production in the body. In fact, research conducted on rats that were given aspartic acid and asparagine found that they were able to exercise longer before reaching exhaustion.
Cysteine is involved in the creation of other amino acids, but its most important function is the synthesis of glutathione, the body’s most powerful antioxidant.
Glutamic Acid, also known as glutamate (yes, as in monosodium glutamate — it’s responsible for the savory flavor known as “umami”), is the most prevalent neurotransmitter and is also the amino that is most taken up by muscle tissue. Once there, it’s converted into glutamine.
Glutamine technically is a conditionally essential amino acid, which means there might be times when the body requires glutamine from outside sources. Glutamine is critical to the gastrointestinal tract (which is one reason why supplementing with it is such a good idea — the body will preferentially put existing glutamine to work in the intestines, so having extra left over ensures some will get to muscle tissue) and is implicated in a healthy immune system. But it is also the most prevalent amino in muscle tissue. Glutamine is involved in protein synthesis (which is how muscles grow), can enhance recovery after workouts (which helps preserve and build muscle) and even increases fat burning.
Glycine is a neurotransmitter involved in protein synthesis, but it’s probably best known as one of the aminos that make up the super-supplement creatine. There is also some evidence that glycine supplementation can increase growth-hormone levels. One particularly ancient study (published in the very venerable American Journal of Physiology in 1941) even found a link between glycine supplementation and an increase in muscular strength.
Proline is required in the production and maintenance of collagen and cartilage, two of the body’s connective tissues. Supplementing with proline could potentially improve joint function, skin health and healing after injury.
Serine has several major roles in the body. It is involved in creating cell membranes and the protective sheaths that cover nerves. It also is involved in fat metabolism and regulating moods.
Tyrosine is associated with the production of such hormones as norepinephrine and various thyroid hormones, and it can increase metabolism and energy levels and boost fat loss. It can also enhance focus and improve mood.
Essential Amino Acids
Obviously, the opposite of nonessential aminos are essential amino acids — those that can’t be made in the body and must be gleaned from food sources. Supplementing with these can make the difference between your body having just enough to function normally and having enough to help you create the best body you could possibly have.
Arginine sound familiar? If you’ve ever sought out a pump in the gym, it should. Arginine is converted into nitric oxide (NO) in the body, and NO is responsible for dilating blood vessels. This is beneficial for numerous reasons: It improves cardiovascular health and function; it allows for increased blood flow to muscle tissue, which means muscles will be well-nourished during and after workouts; and it can actually increase muscle size. All that extra fluid rushing into muscle cells causes them to swell (hence the pump), and that swelling can influence permanent growth. Arginine has also been shown to increase growth-hormone levels, which can increase muscle gains, and to decrease fat storage.
BCAAs (Isoleucine, Leucine, Valine) are three molecularly similar amino acids absolutely essential for muscle growth and maintenance. Unique among aminos, the branched-chain amino acids can be directly used as fuel by the muscles, allowing the body to spare muscle glycogen to extend workouts. BCAAs also help you work out longer by blunting the signals to the brain that the body is fatigued and by reducing perceived exertion, or how hard you feel you’ve been working. They directly influence protein synthesis (aka muscle growth), and leucine blunts appetite and increases metabolism, both of which can increase fat loss.
Histidine joins with beta-alanine to form carnosine. But histidine also produces histamine, which is the compound responsible for the inflammatory response your body produces in response to foreign invaders like pollen or other allergens. Histamine can also increase nitric oxide production, and if you want to know why NO is important, simply glance back to the arginine entry.
Lysine is the culprit when it comes to grains being “incomplete” protein sources. Known as the limiting amino, it is found in insufficient quantities in grains but in large quantities in legumes, which is why eating rice with beans creates a complete protein. One benefit of maintaining healthy levels of lysine outside the scope of bodybuilding is that it can help prevent herpes outbreaks in those who are already infected.
Methionine’s primary importance is in building protein, i.e., muscle tissue, but it’s also involved in creatine production.
Phenylalanine is decidedly brain oriented. It is involved in the synthesis of ephinephrine, norepinephrine and dopamine, three neurotransmitters that have an influence on any number of processes, from fat burning to mood.
Threonine is required for the production of serine and glycine, and it is also implicated in the production of the body’s connective tissues.
Tryptophan, best known for its post-Thanksgiving-feast effects, is the essential amino acid known for being left out of most essential amino acid supplement formulas. Why? Because it increases fatigue during exercise. Why would you want to take it? Well, you wouldn’t, at least not around workout time. Instead, take it to aid sleep and improve mood.