Cake mixes provide a quick, easy dessert for those days when something scratch-made simply isn't an option. Most home bakers know a few ways to vary the mix, either to improve its flavor and texture or to reduce the fat and calories. Using a soda in the mix can accomplish those aims, depending whether it is used to replace just the water or the eggs and oil as well.
Prepare the cake mix as usual, but substitute soda for the amount of water called for on the box. The soda provides a degree of extra leavening from its bubbles, making the cake rise better and providing a lighter texture.
Use the soda to add a complementary flavor to the cake. Cola and root beer can be used with chocolate cake, for example, while cream soda or lemon-lime are compatible with white or yellow cakes.
Reduce the fat in a cake by using soda to replace the oil and eggs, as well as the water. The cake will still have a tender and moist crumb, but will be somewhat chewier than usual. A diet soda may be used rather than regular soda, which will further reduce the total calories in the cake.
Pour the modified batter into cake or muffin pans and bake according to the directions on the box. Cool completely before frosting or packing.
If your goal is to reduce fat and calories, start by replacing only half the eggs and oil with the soda. If the texture is still acceptable, you can then try replacing the other half. One 12 oz. can of soda and one standard box of cake mix will produce a usable cake.