Melted butter and margarine both give brownies a richer taste than oil, but require an additional two minutes of baking time. Regardless of which alternative you choose, melting it to a liquid state and letting it cool before adding it to the brownie recipe is a must. Use 1/4 cup more butter or margarine than you would oil to account for fat content. For instance, if your brownie recipe calls for 1/4 cup of oil, substitute 1/2 cup of melted butter or margarine. Test the brownies for doneness approximately 10 minutes prior to the end of the baking time to prevent dryness.

Fruit-based fat replacements, located in your supermarket’s baking aisle, are commercially prepared fruit purees often containing prunes or apples, designed specifically for the purpose of reducing the fat content of baking recipes. Applesauce and fruit purees can be used as well. Cut the oil measurement in half when substituting a fruit-based fat replacement for oil in a brownie recipe. In other words, if your brownie recipe calls for 1/2 cup of oil, use 1/4 cup of the fruit-based fat replacement, checking the brownies for doneness 10 minutes prior to full bake time.

Yogurt and buttermilk are two dairy-based substitutes for oil in brownie recipes. Add 3/4 cup of yogurt or buttermilk to account for the missing fat. As with all oil substitutes, it may be necessary to cut back on baking time to prevent dryness. Test the brownies by pressing a toothpick into the brownies 10 minutes before the end of baking time to check for doneness.

It is a common misconception that melted vegetable shortening is a feasible substitute for oil in baking. This is not the case. Vegetable shortening is a solid fat, which makes it incompatible -- melted or not -- with oil, which is a liquid fat. Substituting melted vegetable shortening for oil in your brownie recipes may alter the taste and texture of the final product to such an extent that it is unpalatable.