These amino acids become essential under times of stress and illness. Conditionally essential amino acids are in high demand for many metabolic processes. If the body undergoes extensive periods of higher intensity exertion, or is responding to infection or injury, the body may not be able to produce them at a sufficient rate to keep up with the demand. The conditionally essential amino acids include: serine, glycine, ornithine, glutamine, tyrosine, cysteine and arginine.