Preheat the oven to 160°C (325°F) and line an 8 x 4-inch loaf pan with parchment paper.
Place the egg whites and 1/4 teaspoon salt in a large dry bowl. Using a hand mixer or stand mixer with the whisk attachment, beat until stiff peaks form, about 5–7 minutes.
Reduce the mixer speed to low and add the whey protein powder, almond flour, psyllium husk powder, and baking powder. Mix just until evenly combined, scraping the bowl as needed.
Transfer the batter to the prepared loaf pan with a spatula and smooth the top into an even layer.
Bake for 30 minutes. After 30 minutes, turn the oven off and crack the oven door open slightly to allow the loaf to cool slowly inside the oven.
Leave the loaf in the cooling oven for another 30 minutes, then remove it, let cool briefly on a rack, and slice to serve.