Preheat the oven to 160°C (325°F) and line an 8 x 4-inch loaf pan with parchment paper.
In a large dry mixing bowl, combine the egg whites and 1/4 teaspoon salt.
Using an electric hand mixer or stand mixer, beat the egg whites on medium-high until stiff peaks form, about 5–7 minutes.
Add the whey protein powder, almond flour, psyllium husk powder, and baking powder to the whipped egg whites and fold or whisk on low speed until just combined and uniform.
Transfer the batter to the prepared loaf pan and smooth the top with a spatula so it is even.
Bake for 30 minutes. After 30 minutes, turn the oven off and prop the oven door open slightly to allow the bread to cool slowly inside.
Leave the loaf to cool in the oven for another 30 minutes, then remove it from the oven, take it out of the pan, and slice to serve.