Preheat oven to 350° F.
In a bowl, combine bran, flour, sugar, cinnamon, baking powder, baking soda, salt, and apples.
In another bowl combine sweet potatoes, egg, egg whites, oil, and yogurt. Add sweet potato mixture to flour mixture and stir all ingredients until just mixed.
Spray muffin tins with vegetable cooking spray and spoon 1/4 cup of batter per muffin.
Bake for 20 to 25 minutes or until done.Servings: about 20 muffins