How do I add back in the taste and fat to low fat alfredo sauce?
Generally lowfat sauces use tricks to get texture and some semblance of flavour. Starches and thickeners give the illusion of richness, while vast quantities of salt somewhat mask the lack of cheese and butter. Anyone with half a palette can tell at first taste though.
Make it seldom, but make it properly.
Throw out the low-fat sauce. Make alfredo.
Alfredo is a very, very simple sauce at its heart. Most recipes consist essentially only of two or three ingredients such as cream, butter, and parmesan, perhaps with some garlic or pepper.
So if you don't have low-fat restrictions, don't use a low fat version as a base. Just make the sauce from your recipe of choice.
Try brightening the flavor by using herbs and flavors that go well with a cream base. Use your low fat sauce as the creamy background to highlight fresh chives, basil or lemon zest - or all three. Try adding sautéed mushrooms to the recipe if they're not already in it or top the dish with a light drizzle of truffle oil. And Aleppo pepper is a fabulous way to heighten flavor and add some zip. (My favorite brand is Penzey's.)