Quick reply as no one else has
I will come at this from a diferent angle if thats ok.I assume that you know the difference between Carbs, Fats,Proteins etc.Recomended proportions vary according to diet and nutrition fashions of the day(make sure you have sufficient vits, mins and essential amino acids in your diet).However study hard before embarking on anything radical such as a strict Atkins or such.
Firstly a six or twelve pack does not neccessarily denote health or fitness.Genetic make up and body types vary as to an individuals ideal fat index.
If indead you are carrying a few more than is ideal then...
Maybe you know of someone who over eats without thought and is maybe 300 lbs.Notice how this figure varies by very little.Somehow they maintain 300.Many boxers I have Known struggle to lose 2lb for a fight despite eating almost nothing but air.It would seem that the body has a predetermined weight that it fights to retain.
This set weight can be reset I believe with the help of your mind.Simplified this means asking your own unknown wisdom what is a safe healthy weight you can gain (to lose weight is to gain the weight you want I Know this sounds back to front but who wants to lose anything).Then as vividly as you can practice imagine how you would look and feel then step or run if you like running into that body and test that it feels good .Repeat untill ideal. there you have just reset your brain /body weight. hope thats a start