There are several low-fat substitutions that you can use in Alfredo sauce to reduce the fat content without sacrificing flavor. Some options include using low-fat milk or half-and-half instead of whole milk, using low-fat cream cheese or Greek yogurt in place of heavy cream, and adding pureed vegetables such as cauliflower or butternut squash to the sauce to give it a creamy texture. You can also try using a combination of these substitutions to find the right balance of flavor and consistency for your Alfredo sauce.