L-carnitine is best known for its role in transporting fatty acids into the mitochondria, where fat-burning takes place. Recently, researchers at the University of Nottingham in the United Kingdom found that if they raised blood insulin when carnitine was taken, muscle carnitine levels increased at a faster rate than when subjects got carnitine supplements alone.
The researchers infused insulin at a steady rate for six hours with 60 millimoles of carnitine. They reported an increase of total muscle carnitine by 15 percent as well as a dramatic increase in muscle glycogen.
The results validate the notion that increasing muscle carnitine decreases carbohydrate oxidation, or burning, and increases glycogen storage and fat burning. To get a similar benefit, take L-carnitine after your workout with a postworkout shake that contains about 60 grams of fast carbs to spark an insulin surge.
—George L. Redmon, Ph.D.
Stephens, F.B., et. al. (2006). Insulin stimulates L-carnitine accumulation in human skeletal muscle. FASEB Journal. 318:51-61.