Do I have to use whole milk in a white sauce? I am using a roux to thicken and I am worried about the fat content.

An edit function, please! Why are you worried?

Why are your worried?

More fat makes most things "taste" better--a lot of it is mouth feel--but often if not tasted side-by-side, diners are perfectly happy with lower fat. It also depends on what the white sauce will be used for. The more complexity in the dish, the less dependent it will be on white sauce itself. For everyday I use skim or 1%. On a feast day when we are splurging I use whole. It is also possible to use Wondra flour to thicken a white sauce if you are really concerned with the fat content of your sauce. You can then add a little butter for flavor if you want to, but it doesn't have to be as much as making a roux.

I've had no problem using skim milk...but if you want that nice French taste, use whole.

Does the lower fat content effect flavor?

No.. I actually use skimmed may just have to cook a tiny bit longer to thicken