Brownies can be a truly decadent dessert, with up to a cup of butter or oil used to make just one 9-by-13-inch pan. You don't have to use this much fat, however, because there are plenty of healthy substitutions you can experiment with. Soon you'll find a healthier brownie recipe you like that will fit into your diet as an occasional treat.

One of the more common substitutes for oil or butter in baking is mashed or pureed fruit. Replace up to half of the oil in your brownie recipe with mashed bananas, unsweetened applesauce or pureed prunes. You may need to shorten the baking time by about 25 percent if you make this substitution, according to the Ohio State University Extension.

Soft or silken tofu can also replace up to half of the fat in brownies. Tofu doesn't have a strong flavor, so it doesn't alter the taste of your brownies. It also adds extra calcium and protein to the recipe. Some recipes for healthier brownies replace half of the oil with tofu and the other half with pureed fruit for an almost fat-free brownie.

Replacing about half of the fat in your brownies with pureed beans will increase the nutrients in your brownies as well, and you can use either white or black beans. Black beans work best when the brownies have a strong chocolate flavor, while white beans have such a mild flavor they aren't noticeable even in brownies that don't contain a lot of chocolate. A study published in the "Journal of the American Dietetic Association" in 2005 found that replacing up to half of the fat in a brownie recipe with cannellini beans didn't significantly affect the flavor, texture or tenderness of the brownie.

If you're not worried about the amount of fat in your brownie but are just out of oil, you can use either butter or shortening, but this will increase the saturated fat in your brownie compared to using oil. You can make your brownies even healthier by reducing the sugar called for in the recipe by 25 percent. This works especially well if the recipe contains fruit puree, cinnamon, or vanilla or almond extract because these will all help enhance the sweet taste of the recipe.