The first principle of yoga philosophy is ahimsa, which means nonharming to self and others. Some people interpret this to include not eating animal products. There is debate about this in the yoga community—I believe that it is a personal decision that everyone has to make for themselves.
If you are considering becoming a vegetarian, be sure to take into account your personal health issues as well how your choices will affect those with whom you live. Being a vegetarian should not be something that you impose on others—that kind of aggressive action in itself is not an expression of ahimsa.