Lightly spoon flour and cornmeal into dry measuring cups; level with a knife. Combine flour, cornmeal, sugar, baking powder, and salt in a medium bowl, stirring with a whisk. Make a well in center of mixture. Combine buttermilk, oil, and egg whites; add to flour mixture, stirring just until moist.
Spoon batter into 10 muffin cups coated with cooking spray. Sprinkle evenly with cheese. Bake at 425° for 10 minutes or until muffins spring back when touched lightly in center. Remove muffins from pan immediately; place on a wire rack. Serve warm.