I'm no expert, but I think when you're trying to loose weight you should be aiming for 40% of your total calories coming from carbs, 30% proteins and 30% fat.
To be honest I don't think I hit the fat part though as I avoid anything with a high fat content. I've never worked it out though - I just focus on total calories and eat lots of veg to keep me full.
I think if you put your foods eaten into Fitday it will calculate for you what percentages you are consuming.
Hope that helps