You have seen the reports. Some two-thirds of present day Catholics do not believe that they are actually receiving the Body and Blood, Soul and Divinity of Our Lord in the Eucharist; and many do not realize that their belief in this regard is at odds with the perennial teaching of Holy Mother Church. How can this be ?
In St. John's Gospel, Jesus says: "Amen, amen I say to you, unless you eat the flesh of the Son of Man and drink his blood, you do not have life within you. Whoever eats my flesh and drinks my blood has eternal life, and I will raise him on the last day. For my flesh is true food, and my blood is true drink. Whoever eats my flesh and drinks my blood remains in me and I in him." (John 6:53-56) Taking our Lord at His word, the Fathers of the Council of Trent declared that, "Because Christ our Redeemer said that it was truly his body that he was offering under the species of bread, it has always been the conviction of the Church of God, and this holy council now again declares, that, by the consecration of the bread and wine, there takes place a change of the whole substance of bread into the substance of the body of Christ our Lord and of the whole substance of wine into the substance of his blood. This change the holy Catholic Church has fittingly and properly named transubstantiation." (D. 1642)
The Second Vatican Council did not (and could not) alter the solemnly defined doctrine of Transubstantiation. As Pope Paul VI observed in his encyclical Mysterium fidei (Sept. 6, 1965), "The presence [of Christ in the Eucharist] is called 'real', not to exclude the idea that [other modes of presence] are 'real' too, but rather to indicate presence par excellence, because it is substantial and through it Christ becomes present whole and entire, God and man. And so it would be wrong for anyone to try to explain the manner of presence by dreaming up a so-called 'pneumatic' nature of the glorious body of Christ that would be present everywhere; or for anyone to limit it to symbolism, as if this most sacred sacrament were to consist in nothing more than an efficacious sign 'of the spiritual presence of Christ and of his intimate union with the faithful, the members of his Mystical Body.' As a result of transubstantiation, the species of bread and wine undoubtedly take on a new signification and a new finality, for they are no longer ordinary bread and wine but instead a sign of something sacred and a sign of spiritual food; but they take on this new signification, this new finality, precisely because they contain a new 'reality' and that we can rightly call ontological. For what now lies beneath the aforementioned species is not what was there before, but something completely different; and not just in the estimation of Church belief, but in reality, since once the substance or nature of the bread and wine has been changed into the body and blood of Christ, nothing remains of the bread and the wine except the species -- beneath which Christ, whole and entire in his physical 'reality', is even corporeally present, although not in the manner in which bodies are in a place." (D. 4412-4413)
While Catholic doctrine has not changed, Catholic observance and practice regarding the Eucharist has changed, and changed substantially, in ways that have undermined the traditional belief of Catholics.
Transubstantiation is tough going. Jesus' declaration that His flesh was true food and His blood true drink was met with hostility. "This saying is hard; who can accept it?" (John 6: 60) Even the disciples were "murmuring" (John 6: 61), and many "returned to their former way of life and no longer accompanied him." (John 6: 66) The Fathers of Trent, acting as they were in the wake of serious challenges by Protestant reformers, were very conscious of this problem, and they erected an array of protections to reinforce true Catholic belief. The Council declared that the faithful must venerate the Sacrament with the worship of latria that is due to the true God (D. 1643); that there should be special feast days where the Sacrament should be hailed with particular veneration and solemnity and carried in Eucharistic procession (D. 1644); that the Holy Eucharist should be carefully reserved in a sacred place (D. 1645); that Christians must prepare to receive the Sacrament worthily (D. 1646); and that the laity should receive communion from the priest (D. 1648). These salutary teachings were integral to the worship of ordinary Catholics, reflected in Eucharistic fasts, frequent confession, receipt of Holy Communion kneeling and on the tongue, Benediction, Corpus Christ processions, etc. In the wake of the Second Vatican Council, these observances were eliminated almost in toto: the fast was reduced to a single hour, confession has become infrequent, Communion is received standing and in the hand, Benediction and Eucharist processions have been all but suppressed.
The consequence, as we now know, is that some two-thirds of present day Catholics no longer believe that they are receiving the Body and Blood, Soul and Divinity of Our Lord in the Eucharist. Shaped by the priest's celebration of Mass versus populum instead of ad orientem, these Catholics are prone to experience Christ's presence in the praying community instead of in the Eucharistic elements.
"Where two or three are gathered in My name, there am I." As Pope Paul VI observed, this mode of presence is "real", but it is not the Real Presence par excellence whereby Our Lord Jesus Christ through the mystery of Transubstantiation gives us his very body and blood in the Holy Eucharist, so that we may abide in Him, and He in us.