The effect of l carnitine on fat oxidation, protein turnover, and body composition in slightly overweight subjects. Semantic Scholar Does L carnitine produce a clinically meaningful effect within four hours? The Role of l Carnitine in Mitochondria, Prevention of Metabolic Inflexibility and Disease Initiation In terms of fat burning ability.. L Carnitine may not be the brightest star in the sky, but it has another effect that few people actually know about. This content is for educational