consubstantiation, in Christianity, doctrine of the Eucharist affirming that Christ’s body and blood substantially coexist with the consecrated bread and wine. The doctrine gained acceptance in the Protestant Reformation, though the term is unofficially and inaccurately used to describe the Lutheran doctrine of the real presence—namely, that the body and blood of Christ are present to the communicant “in, with, and under” the elements of bread and wine. Consubstantiation differs radically from the Roman Catholic doctrine of transubstantiation, which asserts that the total substance of bread and wine are changed into the substance of the body and blood of Christ at the moment of consecration in such a way that only the appearances of the original elements remain.