Proteins are large, complex molecules that do most of the work in cells and serve as the body's primary building blocks for muscle, bone, skin, hair, organs, and other tissue. This vital structural component of the body:

1. Builds and maintains muscle and bone mass
2. Promotes a strong immune system
3. Transports iron, fats, minerals, and oxygen (in particular, the protein hemoglobin transports oxygen to muscles through the bloodstream)
4. Helps produce enzymes, hormones, antibodies, and blood platelets.
5. Provides energy as a last resort (in the case of carbohydrate and fat store depletion)

Unlike carbohydrates or fat, the body does not generally store deposits of protein for future use. Our bodies use protein shortly after digestion. In general, protein is the last fuel source used by the body (behind carbohydrates and fat) and really only burned under conditions of starvation.^{1, 2}

While athletes do need more protein than their sedentary counterparts, the vast majority of people living in developed countries get more than enough protein in their diet. Protein deficiencies are extremely rare.

Proteins are essentially long chains of amino acids. Amino acids are organic compounds in protein and the basic building blocks of muscle. While there are hundreds of known amino acids, only 23 are proteinogenic (meaning "protein-building"). Of these 23, there are 20 that are known as the "standard" amino acids because these are the only ones that are biologically active in humans.³

Nine of the protein-building amino acids are known as "essential amino acids" (for humans) because they cannot be produced (synthesized) by the body and, therefore, must be consumed in food. The nine essential amino acids are histidine, leucine, lysine, isoleucine, methionine, phenylalanine, threonine, tryptophan, and valine. Your body can synthesize nonessential amino acids. The body easily synthesizes the remaining five amino acids: alanine, aspartic acid, asparagine, glutamic acid, and serine.³

Foods that contain all nine essential amino acids are known as "complete proteins." Incomplete proteins lack one or more essential amino acid; however, incomplete protein food sources can form complete proteins when digested within a few hours of each other.³

There are six "conditionally essential amino acids" that in extreme cases are difficult for the body to synthesize when inhibited by various pathophysiological (disordered physiological processes associated with disease or injury) conditions; these include arginine, cysteine, glycine, glutamine, proline, and tyrosine. Conditionally essential amino acids are nonessential amino acids that may under certain circumstances become essential.²⁹

All whole foods (natural, unprocessed foods) contain amino acids. Yes, plants contain the full spectrum of essential amino acids! Pea and rice protein, soybeans, quinoa, and spirulina contain all 8 essential amino acids, which is especially useful for vegans who want to maintain a high protein diet. However, it is important to note that many vegans do not eat enough lysine. Foods high in lysine include legumes (soy, peas, beans, lentils, and peanuts), seitan (wheat gluten), amaranth (a protein powerhouse grain), quinoa, pistachios, and pumpkin seeds.^{4, 5}

Protein denaturation (the process through which the structural organization of protein's amino acids changes when exposed to heat, concentrated inorganic salt, or strong acids or bases) can affect solubility and synthesis within your body. To learn more about this phenomenon, click here.