Nature's Bounty Acetyl L Carnitine HCl 400mg (30 Capsules) Manmohni Hepatic selective insulin resistance at the intersection of insulin signaling and metabolic dysfunction associated steatotic liver disease: Cell Metabolism L Carnitine for PCOS: Benefits, Dosage & Sources Explained Aiwo Limited L carnitine is a naturally occurring amino acid structure that is made in the human brain, liver, and kidneys. L carnitine plays a critical role in energy production, as it converts fat into energy.