In my business I use cake mixes for all my decorated cakes. To keep them moist, I substitiute applesauce for all of the butter or oil called for. I use only egg whites, and never egg yolks to keep it light and spongy. I do add one extra egg white. For example, if the box calls for 3 eggs, I use 4 egg whites.

You can also substitute any baby food fruits or mashed canned fruits for the applesauce with no taste difference. Hope this answers your question!