EWTN Catholic Q&A
Question from KB on 12-23-2012:

After receiving Holy Communion how long does the Eucharist stay in a person? St. Faustina said that when she received Holy Communion that Our Lord stayed in her until her next Holy Communion. Is this a priviledged grace that only certain people get to receive and can you name other Staints who had that privilege? Thank you

Answer by Richard Geraghty on 12-25-2012:

Dear KB,

The usually explanation of theologians is that Christ remains in us in a physical way as long as it takes for the host to be digested, which is about 15 minutes.

Dr. Geraghty