Pope Francis has said that bread used to celebrate Christian service the Eucharist must not be gluten-free bread, but can be produced from genetically modified organisms.

In a letter to bishops regarding the bread and wine for the Eucharist, the Vatican outlined that the bread must be unleavened, purely of wheat, and recently made, so that there was no danger of decomposition.

He added that bread made from another substance, even if it was grain or mixed with another substance, would not be suitable.

However, breads that are partially gluten-free are deemed appropriate as long as they do not contain “foreign materials without the use of procedures that would alter the nature of the bread”.

Roman Catholics believe bread and wine served at the Eucharist are converted into the body and blood of Christ through a process known as transubstantiation.

“It is a grave abuse to introduce other substances, such as fruit or sugar or honey, into the bread for confecting the Eucharist,” the letter said. “Hosts should obviously be made by those who are not only distinguished by their integrity, but also skilled in making them and furnished with suitable tools.”

Coeliac UK responded to the letter from the Vatican, saying that the current position of the Roman Catholic Church had not changed.

“We are pleased that there is still a provision for people with coeliac disease to observe the Eucharist,” said Sarah Sleet, chief executive of Coeliac UK. There are communion wafers available on the market that have a minimum content of wheat sufficient to be considered acceptable to the Catholic Church’s rules.

“These products are made from gluten-free (Codex) wheat starch and are either labelled gluten-free or very low gluten. Other churches allow communion wafers to be taken which are made entirely from gluten-free ingredients, so often church suppliers sell two different varieties.”