Recently I wrote a mail to my colleagues Priyo and Arnab on the science of diets. I am reproducing the text for that mail for general consumption. Note that before you start a diet, you have to know how much calories your body needs to survive (RMR) and how much you will need to eat to maintain your existing lifestyle (BMR). Not the simple trick is to eat above the BMR to gain mass and lower than BMR to loose mass.
What to eat, when to eat, how much to eat and how frequently, are subjects of a subsequent post. In this one, we will calculate RMR and BMR first. Here we go...
Here's a very brief, simple, and concise way to calculate caloric needs. This is the first step to your lifestyle revamp.
Step #1: Resting Metabolic Rate
Resting metabolic rate (RMR) is the energy it costs the body to basically keep alive. This doesn't include the costs of getting your butt out of bed and moving around; those numbers are calculated in later. Although you might not guess it, about 50 to 70 percent of your entire day's calorie expenditure is a result of the RMR. So, let's figure out your RMR right now.
To start off with, you need to take your body weight in kilograms.
Next you take your percent of fat ( Priyo and Arnab, we can assume us to be around 20%. If you want to get exact figure, you might need to get a check at VLCC etc. for a caliper test) and multiply it by your body weight (which is now in kilograms). This will give you your fat mass (FM) in kilograms. Next simply subtract this number from your total weight in kilograms and you'll have your fat free mass (FFM) in kilograms.
Before we go on, why don't we try this out on me. Since I'm with a body weight of 200lbs at 20% body fat, I'd take my total body mass and divide it by 2.2:
Total body mass in kilograms = 200lbs / 2.2 = 91 kg
Next I'd multiply this kilogram number (91 kg) by my percent of body fat. Remember, percents are really decimals so 20% equals 0.2, 12% bodyfat will be .12 etc.
Fat Mass = 91kg x 0.2 = 18.2 kg FM
Next I subtract this fat mass number (18.2 kg) from my total body mass (91kg):
Fat Free Mass = 91kg - 18.2 kg = 72.8 kg
Therefore my fat free mass is 72.8 kilograms. From that I can determine my RMR. The formula for RMR is as follows:
Resting Metabolic Rate for Athletes (in calories per day) = 500 + 22 x fat free mass (in kilograms).
Again, for me, I'd multiply 22 times my fat free mass and add 500 to that number as shown below:
RMR= 22 x 72.8 + 500 = 2102 (approx)
Therefore my resting metabolic rate is about 2100 calories per day. Everyone have their RMR figured out? Good, let's move on.
Step #2: Cost of Activity
The Cost of Activity represents how many calories are required to move your butt around during the day. This includes the cost of walking out to your car, playing with your pet, driving to work, going to lunch, and of course, training after work. These factors make up about 20 to 40% of your daily caloric intake based on your activity level. So let's figure out your costs of activity. I'll use myself as an example again.
Determining Activity Costs:
Cost of Daily Activity is equal to the RMR you calculated above multiplied by an activity factor that fits your daily routine. I've listed some common activity factors below:
1.2-1.3 for Very Light (bed rest)
1.5-1.6 for Light (office work/watching TV)
1.6-1.7 for Moderate (some activity during day)
1.9-2.1 for Heavy (labor type work)
Note: Don't consider your daily workout when choosing a number. We'll do that later.
With this information we can get back to determining my calorie needs. I've selected 1.6 as my activity factor. Therefore the amount of calories it takes to breathe and move around during the day is about 3400 calories as shown below:
RMR x Activity Factor = 2100 calories x 1.6 = 3362 calories or approx 3400 calories
Costs of Exercise Activity:
Next, we need to determine how many calories your exercise activity burns so that we can factor this into the totals. Exercise activity can be calculated simply by multiplying your total body mass in kilograms (as calculated above) by the duration of your exercise (in hours). Then you'd multiply that number by the MET value of exercise as listed below. (MET or metabolic equivalent, is simply a way of expressing the rate of energy expenditure from a given physical activity.)
MET values for common activities:
high impact aerobics? 7
low impact aerobics? 5
high intensity cycling? 12
low intensity cycling? 3
high intensity walking - 6.5
low intensity walking - 2.5
high intensity running? 18
low intensity running? 7
circuit-type training? 8
intense free weight lifting? 6
moderate machine training? 3
So here's the formula:
Cost of Exercise Activity = Body Mass (in kg) x Duration (in hours) x MET value
And here's how I calculate it for myself:
Exercise Expenditure for weights = 3 METS X 91kg x 1 hours = 273 calories
Exercise Expenditure for cardio = 3 METS X 91 kg x .5 hours = 137 calories
Add these two together and I burn 374 total calories during one of my training sessions.
If you are not doing any training/cardio, your score will be zero. Remember not to cheat with these calculations!
Since my training includes about 60 minutes of moderate free weight training and 30 minutes of low intensity bicycling (four times per week), my exercise energy expenditure is around 400 calories per training day!
The next step is to add this exercise number to the number you generated when multiplying your RMR by your activity factor (3400 calories per day in my case).
So 3400 calories + about 400 calories = a whopping 3800 calories per day! And we're not done yet! (Note: I rounded 374 up to 400 for the sake of simplicity. If you're a thin guy trying to gain muscle, it's better to round up anyway than to round down.)
Step #3: Thermic Effect of Food
TEF is the amount of calories that it takes your body to digest, absorb, and metabolize your ingested food intake. This makes up about 5 to 15% of your total daily calorie expenditure. Since the metabolic rate is elevated via this mechanism 10 to 15% for one to four hours after a meal, the more meals you eat per day, the faster your metabolic rate will be. This is a good thing, though. It's far better to keep the metabolism high and eat above that level, than to allow the metabolism to slow down by eating infrequently. Protein tends to increase TEF to a rate double that of carbs and almost triple that of fats so that's one of the reasons why I'm a big fan of protein meals.
Determining the Thermic Effect of Food:
To determine the TEF, you need to multiply your original RMR value (2100 in my case) by 0.10 for a moderate protein diet or 0.15 for a high protein diet. So this is what the formula looks like:
TEF = RMR x 0.10 for moderate protein diet (1 gram per pound of bodyweight)
TEF = RMR x 0.15 for high protein diet (more than 1 gram per pound of bodyweight)
Since I eat a moderately high protein diet (about 100 to 200 grams per day), I use the 0.10 factor and my TEF is about 210 calories per day as displayed by the calculation below:
Thermic Effect of Food = 2100 calories x 0.10 = 210 calories per day
Now add that to your calorie total.
Step #4: Adaptive Thermogenesis
I like to call Adaptive Thermogenesis the "X factor" because we just aren't sure how much it can contribute to daily caloric needs. Some have predicted that it can either increase daily needs by 10% or even decrease daily needs by 10%. Because it's still a mystery, we typically don't factor it into the equation.
Just for interest's sake, one factor included in the "X factor" is unconscious or spontaneous activity. Some people, when overfed, get hyper and increase their spontaneous activity and even have been known to be "fidgety." Others just get sleepy when overfed ? obviously the fidgeters will be burning more calories that the sleepy ones.
Other factors include hormone responses to feeding, training, and drugs, hormone sensitivity (insulin, thyroid, etc), stress (dramatically increases metabolic rate) or temperature induced metabolic changes (cold weather induces increased metabolic activity and heat production).
With all that said, you don't need to do any math on this part or fiddle with your calorie total. This is just something to keep in mind.
Step #5: Putting it all together
Okay, so how many damn calories do you need to consume each and every day? Well, adding up RMR plus activity factor (3400 calories in my case), cost of weight training (273 calories), cost of cardio (137 calories), and TEF (210 calories), we get a grand total of about 4020 calories! (Remember, that's just my total. You'll get a different number.)
Hence my caloric threshold is 4000 calories. If I eat less that that, I will lose and if I eat more I will gain. Since we are trying to lose, we need to be less than this threshold.
Suggested is to reduce 500-750 calories per day to lose weight healthy increasing your spend on exercise.