Hi
I agree that the calorie mismatch is irritating. No, don’t buy reduced fat yoghurt because the less fat, the more sugar and therefore carbs.
I suggest either
A) plan in your calculation of the calories into your 800 calories or
B) reduce the quantities of everything until you get to the right calories.
I found I had more control being inspired by recipes, but weighing them out on MFP and cooking myself.
Hope that helps. 🙂
By the way remember that fat is not the villain we have been told – it’s too many (especially refined) carbs. So full fat everything, remembering to count it in the calories. 🙂