Amino acids are called the building blocks of protein because different combinations are joined to make proteins. There are 20 different amino acids, and two types, essential and nonessential. Your body can make nonessential amino acids, and you can get them by eating certain foods. Essential amino acids can not be made, so you must get them from a food source.
If a food has all the essential amino acids, it's considered a complete protein source. Animal sources are complete protein sources, but most plant foods are not. Quinoa, soy, and chia seeds are the exceptions.
The essential amino acids missing from most plant foods are lysine, tryptophan, methionine, and phenylalanine.
Your body depends on lysine for proper growth; to produce carnitine (a nutrient responsible for converting fatty acids into energy), and to help lower cholesterol. It also plays a significant role in the formation of collagen.
Collagen is a fibrous protein that makes up bones, cartilage, and other connective tissues, including the skin and tendons.
Amino acids also play a role in maintaining a healthy metabolism, which is important as you age.
Phenylalanine gets converted into the amino acid tyrosine. You need it to make thyroid hormones, and brain chemicals, including dopamine and norepinephrine, the "feel good" neurotransmitters.
If you're deficient, symptoms could include confusion, low energy, depression, fuzzy thinking, memory problems, and a decreased appetite.
Food sources of phenylalanine are eggs, dairy products, and some nuts and seeds.
How important are amino acids? "Every four days, most of the lining of the gastrointestinal tract and the blood platelets are replaced. Most of the white cells are replaced in ten days. A person has the equivalent of new skin in twenty-four days and bone collagen in thirty years. All this continuous repair and work requires amino acids." from the book, The Healing Nutrients Within
The essential amino acid tryptophan.
Tryptophan plays a vital role in your mood. It makes serotonin, which is a neurotransmitter that makes you feel calm.
In its supplement form, L-tryptophan is used to treat insomnia, stress, anxiety and depression. It's also used to treat migraines. And, because it releases a growth hormone that burns body fat, it's used as a weight control aid.
Food sources of tryptophan include cheese (cottage, parmesan, and Swiss have the highest amount), eggs, milk, nuts (especially almonds), peanuts, peanut butter, soy, Wheat germ, and sesame and pumpkin seeds.
Methionine is known as the antidepressant. Your body uses a combination of methionine and adenosine to produce SAM-e (S-adenosylmethionine). SAM-e relieves depression, elevates mood, and is a powerful antioxidant.
Methionine also helps your digestive system get rid of toxins and heavy metals from the liver and arteries.
Food sources high in methionine include avocado, ricotta cheese, wheat germ, whole milk, eggs, cheese, cottage cheese, and oatmeal.
You can get more than enough protein from your diet without consuming meat. The key is to have a wellplanned, diversified diet that includes many of the foods listed above.
Eric R. Braverman, M.D., The Healing Nutrients Within, (CA: Basic Health Publications, Inc. 2003)
University of Maryland Medical Center, Amino Acids Overview