Jesus said in John 6: "the flesh profits nothing? Who's flesh was he refering to? Answer: his own. In other words, the literal flesh of Jesus does nothing spiritually for our spirits. Eating his flesh profits us nothing.
Who deserted Jesus here? Answer: Those who interpreted him literally.
Notice verse 40. "Everyone who sees the Son & believes in him may have eternal life, and I will raise him up at the last day"
verse 54. "Whoever eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day"
In other words, "eating the flesh" is the same as" believing and seeing Jesus" since both actions produce the same results. Notice also he never says we need to believe that the bread becomes flesh but rather that we need to "eat the flesh"