Preheat the oven to 325°F. Grease a 9 by 5-inch loaf pan.
2
Using a stand mixer with the whisk attachment (or a mixing
bowl and electric hand-held beaters), whip the egg whites until very stiff and the peaks hold their shape, about 10 minutes. (To test whether the whites are ready, turn the whisk upside down; if the peaks fold down on themselves, keep whipping.) Using a rubber spatula, slowly fold in the protein powder.
3
Fill the prepared pan with the “dough.” Bake for 40 to 45 minutes, until golden brown. Let completely cool before cutting or the bread will fall. Cut into 14 slices. Store in an airtight container in the fridge for up to 6 days or in the freezer for up to 1 month.