Preheat the oven to 180°C (Gas Mark 4 / 350°F).
Add the egg whites, caster sugar, oil, tinned pumpkin, and milk to a mixer, and mix well to combine (if you don't have a mixer, just whisk lightly by hand). Add the flour, baking powder and bicarbonate of soda, along with all of the spices, and mix again to combine.
Divide the mixture evenly into two lightly greased loaf tins. Place the tins onto a baking sheet, and into the oven. Bake for around 1 hour, or until the cakes are slightly crispy on top, and a toothpick inserted into the centre comes out clean.
Allow the cakes to cool for 5-10 minutes, then turn them out of the tin, and allow them to finish cooling on a rack.