While ratios are a good way to check balance of Calories, they don't provide a method to get to what your intake needs to be in the first place. Now there are a whole bunch of Models that can help you get to a number. The following is the one I used, there could be better ones, I don't know, the one I am using is working for me presently.
Step 1 - Determine your Basal Metabolic Rate. This rate is the number of calories required to keep you at your current rate. There are several BMR models, I come to believe that the Harris-Benedict Model is representative of my body. The following is a link to page that will calculate your BMR:
Harris-Benedict BMR
Step 2 - Given this number you now can adjust your BMR for factors such as activity rate, your own metabolism characteristics, stress, etc. For me I gave myself a + .3 for working out but a - .2 because currently my metabolism is fairly slow. The end result is to take the BMR number and multiple it by 1.1. My Adjusted BMR number was 3391 x 1.1 = 3730
Step 3 - Determine how much you want to lose per week. Experts indicate that a slow, steady weight loss of 1-2 pounds per week is preferred. While you may experience faster loss rates at the begining of an LC plan, these typically level of by the 4th week.
In my case 2 pounds per week is my goal loss rate. For each pound of weight loss per week you need to subtract 500 calories per day. This mean either expending 500 more calories per day or eating 500 calories per day less. So in my case I take the Adjusted BMR from step 2 and subtract 1000 (500 calories per pound per day x 2 pounds per week). My Target intake calories was 3730 - 1000 = 2730 calories per day.
Step 4 - Back to ratios. Now guidelines suggest anywhere from .6-1 gram of protein per pound of Lean Body Mass is recommended. For people doing resistance training I've heard the recommended minium is 1 gram Protein per pound of Lean Body Mass is the target. So my Protein intake at 200 pounds LBM is 200 grams, which is 800 calories. Taking 2730 - 100 carb calories(25 grams x 4 cal/gr) - 800 Protein Calories = 1803 Calories from fat or 1803/10 cal/gram = 180 grams of fat
180 grams fat = 1800 calories fat = 66%
200 grams protein = 800 calories protein = 30%
25 grams carb = 100 calories carb = 4%
Hope this helps,
Lux