Why do vegetarians need to supplement muscle carnosine?

Most individuals do not consume enough beta-alanine in their diets to increase athletic performance. And, because beta-alanine is most often found in meat sources, vegetarian athletes can have an even greater need to supplement beta-alanine levels. The synthesis of beta-alanine in the liver, the only source available to vegetarians, is very low in humans and can only maintain low levels of muscle carnosine.