Conditionally essential amino acids
Amino acids normally made by the body that become essential (to be obtained from food) in certain situations: growth, illness, intense stress.
Between essential amino acids (never made by the body) and non-essential ones (always made), there is an intermediate category: conditionally essential amino acids. The body normally synthesises them, but under certain conditions demand exceeds production, so they temporarily become « essential ».
The main ones: arginine, glutamine, glycine, proline, tyrosine, cysteine, serine.
A fresh angle (the concept of demand versus production): this « conditional » status illustrates a key idea: nutritional needs are not fixed, they depend on the physiological context
- Growth (infants, children, teenagers): demand soars, so arginine and histidine become essential in infants
- Illness/intense stress (infection, surgery, burns, sepsis): glutamine and arginine are consumed in large amounts and become limiting
- Intense exertion/elite sport: increased needs for certain amino acids
- Deficiencies in synthesis enzymes or a precursor (e.g. tyrosine is made from phenylalanine, so in phenylketonuria tyrosine becomes essential)
Concrete examples and roles:
- Arginine: precursor of nitric oxide (vasodilation, healing, immunity). Crucial in recovery after surgery
- Glutamine: fuel for the gut and immune system (see dedicated term)
- Glycine: collagen, sleep, detoxification (glutathione)
- Cysteine: precursor of glutathione (the master antioxidant)
- Tyrosine: precursor of dopamine, noradrenaline and thyroid hormones
Practical implication: during periods of physiological stress (convalescence, intensive sport, pregnancy), an adequate, good-quality protein intake matters all the more because these « usually optional » amino acids become critical.
Sources: all complete proteins (animal sources and plant combinations) provide these amino acids. Bone broth (glycine, proline), meat (arginine, cysteine), etc.