A slice of bread weighs about an ounce or 28 grams. There is less than 3 grams of protein in a slice of bread. About 80% of the protein is gluten which gives 2.

A slice of bread weighs about an ounce or 28 grams. There is less than 3 grams of protein in a slice of bread. About 80% of the protein is gluten which gives 2.5 grams of gluten per slice. So at the lowest exposure level, 1 milligram, this would mean making sure not to eat 1/2500th of the slice of bread. The slice of bread is about 4 inches by 4 inches by 0.5 inches giving a volume of 8 cubic inches. 1/2500th of that slice is 0.0032 cubic inches or a cubic piece >1/8 inch on each side. Based on the above calculation, I think it's probably ok to use the same utensil as long as there are no obvious crumbs.