[sgc]

Egg whites were used to starch habits and for various other tasks, but communion wafers are pressed bread, and don't have any egg in them at all. I could not find any confirmation of your statement in a reputable source, and I have never heard of such a practice. The Catholic Church has long maintained that the host should be made of wheat flour (in the past sometimes with a small addition of another flour) and water only. Egg whites were used to clarify wine for the Eucharist, which might be the source of that likely fable.