The tradition of the Eucharist, whereas bread and wine is transformed into the body and blood of Christ is carried on by Sacred Tradition of the Universal (Catholic) Church. It is not simply a symbol, and all of the Apostolic founded orthodox churches have carried on this tradition as well. Proof of this tradition can be found in this Biblical document of 1 Corinthians, Chapter 11:
Tradition of the Institution.
23 For I received from the Lord what I also handed on to you, that the Lord Jesus, on the night he was handed over, took bread, 24 and, after he had given thanks, broke it and said, “This is my body that is for you. Do this in remembrance of me.” 25 In the same way also the cup, after supper, saying, “This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me.” 26 For as often as you eat this bread and drink the cup, you proclaim the death of the Lord until he comes. 27 Therefore whoever eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord. 28 A person should examine himself, and so eat the bread and drink the cup. 29 For anyone who eats and drinks without discerning the body, eats and drinks judgment on himself. 30 That is why many among you are ill and infirm, and a considerable number are dying. 31 If we discerned ourselves, we would not be under judgment; 32 but since we are judged by [the] Lord, we are being disciplined so that we may not be condemned along with the world.