see also:

• protein
• dietary_protein
• protein metabolism

• there are 20 amino acids that are the building blocks of peptides which form hormones and proteins
• dietary amino acids and the amino acids that form from catabolism of protein form an amino acid pool which have various fates (see protein metabolism)
• regular protein intake is essential for health as this is the main source of dietary amino acids, particularly so for the “essential” amino acids
• inadequate intake results in “protein malnutrition” which can result in:
  • impaired protein production including hypoalbuminaemia, impaired immune responses, muscle wasting and sarcopenia / generalised muscle wasting, etc
    • in chronic extreme cases it causes Kwashiorkor - a severe protein deficiency state seen in starving children in Third World countries
• excessive amino acid intake for the body's needs (the daily requirements change with activity levels such as exercise, growth, pregnancy, ageing, etc) though has been associated with reduced longevity in many species including humans and may cause a range of pathology
  • this seems to be especially the case for methionine, isoleucine and valine¹⁾
• glutamine, glycine, and aspartic acid along with active Vitamin B9/folate are used to make purines which break down to uric acid
• aspartic acid (aspartate) and glutamine are used to make pyrimidines which break down to urea

• these are required in diet as humans cannot make them or cannot make them in sufficient quantities
• Histidine:
  • protects nerve cells and helps make histamine.
• Isoleucine:
  • aids immune function, energy regulation, and muscle metabolism.
• Leucine:
  • Drives muscle repair, protein synthesis, and growth hormone production.
• Lysine:
  • Supports hormone production, calcium absorption, and immune defense.
• Methionine:
  • Assists with metabolism, detoxification, and healthy tissues.
• Phenylalanine:
  • Converts into key brain chemicals like dopamine and tyrosine.
• Threonine:
  • Builds strong skin and connective tissues like collagen.
• Tryptophan:
  • Acts as a building block for serotonin to control sleep and mood.
• Valine:
  • Stimulates muscle growth and steady energy production

• during major stress, severe illness, or rapid growth phases the human body cannot make enough of them
• Arginine
• Cysteine
• Glutamine
• Glycine
• Proline
• L-Serine

• a naturally occurring, proteinogenic amino acid that plays a crucial role in protein synthesis, central nervous system development, and cellular metabolism.
• while classified as non-essential because the body can synthesize it, it is vital for neurological health and metabolic function
• supports conserved cellular processes including protein synthesis, nitrogen and amino acid metabolism, and the production of essential membrane lipids such as phosphatidylserine, phosphatidylethanolamine, and sphingolipids
• acts as a precursor for D-serine and glycine, which support neurotransmission and NMDA receptor activity in the brain
• essential for creating phosphatidylserine and other sphingolipids vital for neuron survival and cell wall integrity
• helps manufacture other molecules, including cysteine, tryptophan, and cellular antioxidants like glutathione
• dietary sources:
  • found abundantly in high-protein foods such as eggs, soy products, meat, fish, nuts, and lentils
• requirements:
  • can become conditionally demanded in higher amounts during rapid growth, extreme physical stress, or specific neurological conditions
• pathology:
  • in humans, variants in the PSPH gene, which encodes phosphoserine phosphatase, are linked to L-serine deficiency disorders and related neurodevelopmental phenotypes
    • PSPH overexpression is associated with proliferative and metabolic phenotypes in cancer
    • PSPH substitutions such as D32N and M52T can produce a range of effects, from modest or context-dependent changes to marked reductions in enzyme activity, protein stability and interactions, or cellular phenotypes
    • the R27S/D32G haplotype, detected in Alzheimer's disease hippocampal samples, reduces catalytic efficiency

• Alanine
• Asparagine
• Aspartic acid
• Glutamic acid

• D-serine
  • an enzyme called serine racemase converts L-serine into D-serine directly in the brain where it acts as a signaling molecule that binds to NMDA receptors, playing a critical role in memory and learning