Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis L Carnitine has become one of our top 5 sellers the last few years and when you review the research, you can see why. L carnitine is a supplement probably more well known if Combining Berberine and L Carnitine can be beneficial for weight management, metabolism, and overall health. Berberine may improve insulin sensitivity, lower blood sugar, and support weight loss, while L carnitine helps the body use L Carnitine in the treatment of diabetes