Really I'd disagree to some degree using the other two solutions - I believe you should use creme fraiche rather.
To be sure with MStodd that it'll certainly provide a different flavour and texture towards the sauce, but when you are just searching for any healthier base to some pasta sauce, I'd say it's fine to substitute. Also as daniel mentions, you need to be careful to not overheat it (although this is also true of cream), because it will curdle.
In my opinion, creme fraiche is excellent to create a very fast and simple pasta sauce. Place it in right in the finish of cooking, once anything else is correctly cooked and merely heat enough so it's warmed through.
It comes down lower to regardless if you are wanting to offer the same flavours though - if you're, maybe you could attempt things i would call single cream (unsure what it might be known as in america), and thicken the sauce along with some cornflour combined with cold water.
clarified November 2 '10 at 8:13
Used to do finish up using Creme Fraiche as an alternative in my recipe and that i altered it by using only a pint creme fraiche and pasta water to complete a few of the volume and obtain the graceful texture I had been searching for. I allow the sauce get together inside a bowl steamed over my pasta because it cooked therefore the heat was gentle. The sauce would be a success and everybody loved the dish. Varuuknahl November 2 '10 at 13:42
I've effectively made an alfredo-like sauce using sour cream, and so i imagine creme fraiche may also be designed to work. Naturally, the taste will change, but when it has cheese, how will you fail? Marti November 2 '10 at 15:39