Methylmalonic acid is a compound produced in the body during the metabolism of certain fats and proteins. It is primarily formed from the breakdown of amino acids like valine and isoleucine. Normally, the body converts methylmalonic acid into another substance called succinyl-CoA, which is essential for energy production. High levels of methylmalonic acid in the blood can indicate a deficiency in vitamin B12, which is crucial for its metabolism. This condition can lead to various health issues, including anemia and neurological problems. Monitoring methylmalonic acid levels can help diagnose and manage vitamin B12 deficiency effectively.