According to 10% Law, only 10% of energy is transferred from one trophic level to next trophic level. Plants are producers so if man will be vegetarian then he will directly eat plant based foods so will get maximum energy but if he will be non-vegeterian he will eat herbivores like goat, hen that feeds upon plants so man will be at higher trophic level and will get minimum energy as compared to being vegetarian. So accordingly in a food chain man can place himself in an advantageous position. For example- animals which are herbivores get 10% of energy from plants suppose 100 J according to 10% rule. When man will feed upon these animals they get only 10 J which is 10% of 100 J. But if man will feed directly on plants get 100 J hence vegetarians are at an advantageous position and get more energy than non-vegetarians.