It is not permitted to make Communion hosts for Catholic Mass out of anything except wheat flour and water (and, before anyone corrects me, in the Eastern churches also leavening). From the
nutritional information I was able to find for standard white flour, it contains a negligible amount of fat (about one three hundredth part) and about one thirtieth part protein by weight. A typical mass-produced Communion wafer might weigh about a quarter of a gram (see
here; if 1000 wafers is one half pound then one wafer weighs 0.2265 grams). Even if we assume that that weight is all flour, you can see that the amounts involved are very small – to consume 1 gram of protein would require eating some 120 wafers.
We can talk this way about unconsecrated wafers, with the proviso that after consecration, when they become the Eucharist, they still continue to act upon the body as though they had the properties associated with bread. For instance, with Eucharistic wine, we cannot say that it
contains alcohol, since theologically its substance has completely become the Blood (+ Body, Soul, and Divinity) of Christ. However, we know that a person who drinks too much can still become drunk. This is because the Eucharistic species continue to display what are called the “accidents” – i.e., the physical properties – of the bread and wine which they once were.
