"In clinical practice the term amino acid deficiency is commonly used to indicate low plasma levels of specific amino acids. However a more proper definition would be an insufficient flux to maintain full functionality of the concerning amino acid."
https://www.sciencedirect.com/topics/medicine-and-dentistry/amino-acid-deficiency
"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
"Although amino acids are most recognized for their role in muscle development and repair, your body depends on them for so much more.
That’s why essential amino acid deficiencies can negatively affect your entire body, including your nervous, reproductive, immune, and digestive systems.
People can have different amino acid needs based on stage of life, chronic illness, and acute health issues such as an infection or a surgery.
However, most people get all the amino acids they need through their diet."
https://www.healthline.com/nutrition/essential-amino-acids#how-many-are-there
"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. By identifying and analysing these signs, effective treatment and prevention protocols can be implemented so patients can live comfortably in the future."
https://read.iim.health/amino-acid-deficiencies-and-symptoms/
"It’s important to have enough of all aminos for functions like building/repairing muscle, appetite control, and fatigue delay. So if you observe the symptoms from lack of aminos it’s important to boost your levels immediately.
There are several signs of this condition including a higher risk of infection, hair/skin/nail issues, and loss of muscle mass. These could be signs of other conditions so it’s important to look for multiple symptoms to verify that it’s a deficiency of amino acids. The next step is to determine which amino acid is causing the deficiency so you can boost your levels as quickly as possible"
https://aminoacidstoday.com/amino-acid-deficiency/