"In clinical practice the term amino acid deficiency is commonly used to indicate low plasma levels of specific amino acids."
https://www.sciencedirect.com/topics/medicine-and-dentistry/amino-acid-deficiency
"Amino acids serve as key building blocks and as an energy source for cell repair, survival, regeneration and growth. Each amino acid has an amino group, a carboxylic acid, and a unique carbon structure. Human utilize 21 different amino acids; most of these can be synthesized endogenously, but 9 are “essential” in that they must be ingested in the diet."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6331359/
"Although your body can make nonessential amino acids, it cannot make essential amino acids, so you have to get them from your diet.
The best sources of essential amino acids are animal proteins such as meat, eggs, and poultry. However, some plant foods, such as the soy products edamame and tofu, contain all nine essential amino acids. This means they are “complete” sources of protein"
https://www.healthline.com/nutrition/essential-amino-acids#what-they-are
"One of the more obvious reasons for amino acid deficiency is the simple lack of proper nutrition. If your diet lacks the right foods with all essential amino acids, then you will not have them in your physiological arsenal.
One such diet that I often see amino acid deficiencies is a vegetarian or vegan diet. Because most foods on these diets are not complete proteins (not containing all essential amino acids), they require a little more planning to ensure adequate amounts of amino acids are absorbed into the body."
https://drjockers.com/5-reasons-amino-acid-deficiency/
"Amino acids build muscles, cause chemical reactions in the body, transport nutrients, prevent illness, and carry out other functions. Amino acid deficiency can result in decreased immunity, digestive problems, depression, fertility issues, lower mental alertness, slowed growth in children, and many other health issues.
Each of the essential amino acids plays a different role in the body, and the symptoms of deficiency vary accordingly."
https://www.medicalnewstoday.com/articles/324229
"Amino acids are vital in the optimal functioning of the body and can lead to uncomfortable symptoms when not monitored regularly. The development of mood disorders, experiencing a lack of focus and fatigue, and a weak immune system may be signs of an amino acid deficiency"
https://read.iim.health/amino-acid-deficiencies-and-symptoms/
"Amino acid deficiency often gets overlooked, and when left untreated it makes it more likely you’ll develop a whole host of serious disorders."
https://aminoco.com/blogs/health/amino-acid-deficiency-signs