Preheat the oven to 375 degrees. Grease an 8-inch x 4-inch loaf pan with olive oil and line it with parchment paper.

Whisk together the almond flour, tapioca flour, coconut flour, flaxmeal, psyllium husk, salt and baking soda in a bowl until well combined and lump-free.

In the bowl of a stand mixer, combine egg whites, olive oil and apple cider vinegar. Add flour mixture to the egg white mixture and beat on medium-low to combine well. You are not trying to whip the egg whites. Pour in the boiling water and blend on medium-low speed for 1 minute.

Transfer batter to the prepared pan.

Prepare the egg wash: in a small bowl, beat 1 whole egg with water and brush over top of loaf.

Bake for 1 hour and 10 minutes.

Remove from the oven, then carefully remove the loaf from the pan. Place the bread loaf back into the oven right on the oven rack. Bake until loaf forms a golden crust, about 10-15 minutes.

Cool the bread completely on a cooling rack before slicing.

Store bread at room temperature in an airtight container or wrapped well with plastic wrap for up to 3 days. Or store well-wrapped in the refrigerator for up to one week.