Preheat oven to 350°F (180°C) and line a 5×7 inch loaf pan with parchment paper.
In a bowl, mix almond flour, coconut flour, salt, baking powder, baking soda, and xanthan gum.
Stir in yogurt and melted coconut oil until thick.
In a separate bowl, whip egg whites until stiff peaks form.
Gently fold egg whites into the batter until combined.
Transfer batter to the loaf pan, smoothing the top.
Bake uncovered for 35–40 minutes, then cover with foil and bake another 30–40 minutes.
Let cool completely before slicing.