Unleavened bread used in the celebration of Mass cannot be completely gluten-free, the Vatican says.

The policy outlined in a directive dated June 15 states that truly gluten-free altar breads made with rice, potato, tapioca or other flours in place of wheat are not allowed. There must be at least a trace amount of gluten, a protein that occurs naturally in wheat, The New York Times reported.

A similar position was adopted by the Church of England, while some other Christian denominations consider gluten-free breads acceptable.

People with celiac disease are vulnerable to even small amounts of gluten.