http://www.discussbodybuilding.com/m_6526/mpage_1/key_calculate%2Cexp//tm.htm#6526
Diet really isn't that difficult, the willpower to stick to it might be, but the, "How much to eat of what?" question will be answered here.
It all boils down to caloric expenditure, if we have a caloric deficit (expend more than we intake) we lose weight, caloric surplus (intake more than we expend) we gain weight. It is a little more complicated than this... but not much. Our bodies want to maintain a state of homeostasis (remain unchanged), so when we eat more our metabolism increases, when we eat less it decreases. So in order to gain or lose weight we must out eat our natural metabolism adjustment generally accepted to be around 500 calories to lose/gain a healthy amount of weight.
I have used the following diet in preparation for contests, and to gain weight and it has worked for me and everyone I have provided it for... if you eat right. Mike Starks, former national competitor and Exercise Science Guru, gave the diet to me; I think he just finished his doctorate (congrats Mike). So here it is:
Body weight in kgs times 24 hours times 1 for males and times .9 for females. This gives you the basal metabolic rate (BMR). You then multiply the BMR times the activity percent.
Activity percent is based on aerobic activity, since resistance training does not burn that many Kcals we don't consider it as a caloric burn activity. The rule for this is 20% for sedentary, 30 to 40 % if the person does cardiovascular exercise 30 to 45 minutes per day 3 to 5 times a week, 50 to 70 % if the person does 1 hour of cardiovascular exercise per day 5 to 7 times a week, 80 to 100% if the person does more than 1 to 2 hours per day 7 days per week.
After you multiply the activity percent times the BMR you then add the result back into the BMR. You then multiply the result by 10 percent for specific dynamic activity (SDA). Then add this result back into the BMR and activity sums for total caloric requirements.
This is your daily caloric expenditure. To lose a pound a week of fat, reduce the kcals by 500 per day.
To calculate the grams and ratios you multiply your lean weight by 2.2 to 2.5 grams per kg of bodyweight (or just how many lbs you weigh). Multiply this number by 4 to get kcals of protein. You then subtract this number from your total kcals. The remaining Kcals will be divided up between carbohydrates (CHO) and fat. Fat will make up 20% of your total kcals. So you will multiply 20% times the kcals then divide the answer by 9 to estimate grams of fat. The remaining kcals after you subtract out the fat and protein will be the CHO kcals. Divide this number by 4 to get the grams of CHO you will need. This will be what you will use for your diet until your body weight decreases you will then do the whole estimation over again. Below is the formula.
1.) BW x 24 x 1 (for males) BW x 24 x .9 (for females) = BMR
2.) BMR x activity level (percent) = activity Kcals
3.) (BMR + activity Kcals) x 10% = SDA
4.) BMR + activity Kcals + SDA = total kcals required to maintain BW
To lose 1 lb a week, reduce Kcals by 500 per day.
Looks complicated? Naa, I'll do the calculations for a recent poster (6'3", 265 lbs looking to lose weight) asking about diet...
265lbs/2.2lbs/kg=120.5 kg (kg conversion)
1. 120.5*24*1=2892 (BMR)
2. 2892*.35=1012 (activity cals)
Based on 3-5 days of cardio for at least 30 minutes
3. (2892+1012)*.10=390 (SDA)
4. 2892+1012+390=4294 (we'll call it 4300)
So to lose 1 lb of fat per week he should intake 3800 calories a day. If we want to lose weight then we should be doing at least 30 minutes of cardio 4 or 5 times a week that's where the activity % came from. If you want to gain weight (esp. if you have a hard time gaining weight) you want to minimize cardio (not necessarily eliminate it).
So 3800 calories a day (damn that’s a lot, but then again he's a lot bigger than me at 5'7", 185):
Protein intake = body weight in lbs = 265g = 1060 protein cals
Fats = .20 * 3800 (20% of total) = 760 fat cals = 84g
Carbs = 3800 - (1060 + 760) = 1980 carb cals = 495g
So to lose weight he'll START at:
265g protein, 495g carbs, 84g fat.
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