Where in the Bible does it say that the host contains both the body and blood of Jesus?

Not so. In 1 Corinthians 11:27, we read (RSV): “Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of profaning the body and blood of the Lord” [emphasis added]. Whether we eat the host or drink from the cup, we profane both the body and the blood of Christ, so the host consists not only of the body of Christ, but also of his blood. Likewise, the cup consists of not only the blood, but also the body of Christ.