1. The marketed positive outcomes of supplements is often based on theory, not proven science.
There are millions of physiological processes that happen constantly in the body over the course of a day. This opens the door for supplement companies to pick a metabolic process, pull out a nutrient utilized in the process and try to convince you to supplement it. One example of this is L-carnitine, which facilitates the influx long-chain fatty acids (i.e. fat stores) into the mitochondria of cells in order to be utilized for energy instead of using stored carbohydrate, or glycogen. Because of this fact, supplement companies encourage supplementation of L-Cartinine to "enhance fat burning" and "spare muscle glycogen" during exercise. The problem? No studies have shown this to actually happen when L-Carnitine is supplemented. While it may make sense in theory, it doesn't pan out when put to the test.