[7] When twenty active, resistance trained-males were given 2g per day of l-carnitine l-tartrate and prescribed a high-carbohydrate diet (which, interestingly, included alcohol!) and measured for two weeks of exercise, they noticed no change in oxidation of carbohydrates, nitrogen, BCAAs, or plasma urea, as well as no change in fat, carbohydrate, or protein metabolism between baseline measurements, and no difference between the supplemented group and the placebo group
However, they work best as part of a broader approach that includes regular exercise, balanced nutrition, quality sleep, and stress management.
That said, these molecules also have useful roles, such as fighting off infection
and Waqar, M.A., 2014