Glutamine
Glutamine is the most abundant naturally occurring, nonessential amino acid in the human body, and one of the few amino acids that can directly cross the blood–brain barrier. Humans obtain glutamine through catabolism of proteins in foods they eat. In states where tissue is being built or repaired, like growth of babies, or healing from wounds or severe illness, glutamine becomes conditionally essential.
Carnitine
Carnitine (β-hydroxy-γ-"N"-trimethylaminobutyric acid, 3-hydroxy-4-"N","N","N"-trimethylaminobutyrate) is a quaternary ammonium compound involved in metabolism in most mammals, plants and some bacteria. Carnitine may exist in two isomers, labeled -carnitine and -carnitine, as they are optically active. At room temperature, pure carnitine is a white powder, and a water-soluble zwitterion with low toxicity. Carnitine only exists in animals as the -enantiomer, and -carnitine is toxic because it inhibits the activity of -carnitine. Carnitine, derived from an amino acid, is found in nearly all organisms and animal tissue. Carnitine is the generic expression for a number of compounds that include L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine. It is most accumulated in cardiac and skeletal muscles as it accounts for 0.1% of its dry matter. It was first derived from meat extracts in 1905, therefore the name carnitine is derived from Latin ""carnus"" or flesh. The body synthesizes enough carnitine from lysine side chains to keep up with the needs of energy production in the body as carnitine acts as a transporter of long-chain fatty acids into the mitochondria to be oxidized and produce energy. Some individuals with genetic or medical disorders (like preterm infants) cannot make enough, so this makes carnitine a conditionally essential nutrient for them.