Calculating nutrition for bread starter

Does anyone know how to calculate the nutrition for a bread starter? I use the potato flake starter where I am adding 3 tbsps of potato flakes, 3/4 cup of sugar and 1 cup of warm water every week to the starter. One whole cup of starter is usually added to a bread recipe. This is the recipe I have: http://www.justapinch.com/recipes/bread/other-bread/potato-flake-sourdough-starter-and-bread-recipe.html

I realize this may be a difficult request, but if anyone can help me, I would really appreciate it! I love my homemade bread and I like to tweak it here and there to make things healthier for me and my family but I can not do that for my most favorite bread if I don't know what's in that cup of starter I use in a recipe. I usually use my fitness pal to calculate recipes by calories, fat, carbs, fiber and protein. Thanks for any advice anyone can provide!!