The purpose of making a roux is to brown the flour in hot fat so that the "raw" taste is cooked out and brown flavours are developed. However, the same effect could presumably be achieved without any fat by, say, toasting it in a low oven until it's equally browned and then mixing with water to form a slurry. Searching on the web, I've found a couple of references to doing this but it doesn't seem to be too common. It seems to me that this would be a no-brainer for anybody on a low fat diet. You