Spray bottom and sides of an 8 1/2 x 4 1/2 x 3 inch loaf pan with cooking spray. Dust with flour.
Cream sugar and butter at medium speed of electric mixer until light and fluffy. Add egg whites; beat 4 minutes at medium speed until well blended. Add vanilla and beat at low speed until well blended.
Combine flour, baking soda and salt. With mixer running at low speed, add to creamed mixture alternately with yogurt, beginning and ending with flour mixture.
Pour batter into pan and bake in preheated 350 degree oven for 65 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 10 minutes, then cool on wire rack. Serve plain or with fruit.
