My buddy Action on Steroid World put this together and I thought it would be a great post:
Your daily calorie requirements depend on six major factors. The formulas for
calorie calculations you are about to learn take into account all six of these factors to get
the most accurate estimate possible.
1) Basal Metabolic Rate (BMR)
BMR is the total number of calories your body burns for normal bodily functions,
including digestion, circulation, respiration, temperature regulation, cell construction, and
every other metabolic process in your body. In other words, your BMR is the sum total of
all the energy used for basic bodily functions, not including physical activity. BMR
usually accounts for the largest amount of your daily calorie expenditure – about twothirds.
BMR is at its lowest when you’re sleeping and you’re not digesting anything.
BMR can vary dramatically from person to person depending on genetic factors. You
probably know someone who can eat anything they want yet they never gain an ounce of
fat. This type of “fast metabolism” person has inherited a naturally high BMR.
2) Activity Level
Next to BMR, your activity level is the second most important factor in how many
calories you need every day. The more active you are, the more calories you burn; it’s that
simple. Become more active and you burn more calories. Sit on the couch all day long
and you hardly burn any.
3) Weight
Your total body weight and total body size are also major factors in the number of
calories you require. The bigger you are, the more calories you’ll require to move your
body.
4) Lean Body Mass (LBM)
Total body weight correlates with the number of calories you require, but separating your
total weight into its lean and fat components allows you to calculate your calorie needs
even more accurately. The higher your LBM, the higher your BMR will be. This is very
significant when you want to lose body fat because it means the more muscle you have,
the more calories you will burn at rest. Muscle is metabolically active tissue, and it
requires a great deal of energy to sustain it. The best way to increase your BMR is to
increase your LBM. This is why you could say that weight training helps you lose body
fat, albeit indirectly.
5) Age
Metabolic rate tends to slow down with age. Therefore, the number of calories the
average person requires also goes down with age. Fortunately, you can prevent and even
reverse the age-related slowdown in metabolism by developing more muscle through
weight training and nutrition.
6) Gender
Men usually require more calories than women. The average male has a maintenance
level of 2800 calories per day. The average female requires only 2000 calories per day to
maintain. The reason for this difference is not so much a sex-related issue as a body
weight and muscle mass issue; the average man carries much more muscle mass than the
average female and this explains the spread in calorie requirements between men and
women. Except for individual genetically-related differences in BMR, a 140 pound man
and a 140 pound woman would have the same calorie requirements if their activity levels
were identical.
There are many formulas you can use to determine your daily calorie needs using
these six factors. Any formula using LBM in the calculations will always be more
accurate than one based only on bodyweight. However, you can still get a very accurate
estimate of your calorie expenditure just from body weight alone.
The “quick” method (based on total bodyweight)
A fast and easy method to determine how many calories you need is to use your total current weight times a multiplier for TDEE.
Fat loss = 12 – 13 calories per lb. of bodyweight
Maintenance (TDEE) = 15-16 calories per lb. of bodyweight
Weight gain = 18 to 20+ calories per lb. of bodyweight
This is a very easy method to estimate caloric needs, but its most obvious
drawbacks are not taking into account activity levels or body composition. If you’re
extremely active, this formula will underestimate your calorie requirements.
Using this formula, a lightly active 50-year-old woman who weighs 235 lbs.
would have a TDEE of 3055 calories per day (235 X 13). Since almost all women will
rapidly gain weight on 3000 calories per day, this illustrates another flaw in the quick
formula – it will overestimate your calories if your fat is significantly higher than average.
Despite these drawbacks, the quick formula is a good way to get a quick ballpark
estimate, as long as your body fat is average or less.
A more accurate method for calculating TDEE is to determine basal metabolic
rate (BMR) first, then multiply the BMR by an activity factor to determine TDEE. There
are two formulas you can use to calculate your BMR. The Harris-Benedict formula is the
one you will use if you don’t know your LBM (you don’t need body composition
information to use this formula). If you know your LBM, you should use the Katch
Mcardle formula for the most accurate calorie estimate of all.
The Harris-Benedict formula (BMR based on total body weight)
The Harris-Benedict formula uses the factors of height, weight, age, and sex to
determine basal metabolic rate (BMR). This makes it more accurate than determining
calorie needs based on total bodyweight alone. The only variable it doesn’t take into
consideration is lean body mass.
This equation will be very accurate in all but the extremely muscular (will
underestimate caloric needs) and the extremely overfat (will overestimate caloric needs).
Men: BMR = 66 + (13.7 X wt in kg) + (5 X ht in cm) – (6.8 X age in years)
Women: BMR = 655 + (9.6 X wt in kg) + (1.8 X ht in cm) – (4.7 X age in years)
Note: 1 inch = 2.54 centimeters
1 kilogram = 2.2 lbs.
Example:
You are male
You are 30 yrs old
You are 5′ 8 ” tall (172.7 cm)
You weigh 172 lbs. (78 kilos)
Your BMR = 66 + 1068 + 863.6 – 204 = 1793 calories/day
Once you know your BMR, you can calculate TDEE by multiplying your BMR by the
following activity factor.
Activity factor
Sedentary = BMR X 1.2 (little or no exercise, desk job)
Lightly active = BMR X 1.375 (light exercise/sports 1-3 days/wk)
Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)
Very active = BMR X 1.725 (hard exercise/sports 6-7 days/wk)
Extr. Active = BMR X 1.9 (hard daily exercise/sports & physical job or
2 X day training, marathon, football camp,
contest, etc.)
Continuing with the previous example:
Your BMR is 1793 calories per day
Your activity level is moderately active (work out 3-4 times per week)
Your activity factor is 1.55
Your TDEE = 1.55 X 1793 = 2779 calories/day
Katch-McArdle formula (BMR based on lean body weight)
The Harris-Benedict equation has separate formulas for men and women because
men usually have a higher lean body mass and a larger bodies.
Since the Katch-McArdle formula accounts for LBM, this single formula applies
equally to both men and women and it is the most accurate method of determining your
daily calorie needs.
BMR (men and women) = 370 + (21.6 X lean mass in kg)
Example:
You are male
You weigh 172 lbs (78 kilos)
Your body fat percentage is 14% (24.1 lbs fat, 147.9 lbs lean)
Your lean mass is 147.9 lbs (67.2 kilos)
Your BMR = 370 + (21.6 X 67.2) = 1821 calories
To determine TDEE from BMR, you simply multiply BMR by the activity factor:
Continuing with the previous example:
Your BMR is 1821
Your activity level is moderately active (you work out 3-4 times per week)
Your activity factor is 1.55
Your TDEE = 1.55 X 1821 = 2822 calories
As you can see, the difference in the TDEE as determined by both formulas is
statistically insignificant (2779 vs. 2822 calories) because the man we used as an example
is average in body size and body composition. The primary benefit of factoring LBM into
the equation is increased accuracy when your body composition leans to either end of the
spectrum (very muscular or very obese). This is yet another reason to monitor your body
fat percentage and not just your body weight.
Once you know your TDEE (maintenance level), the next step is to adjust your
calories according to your primary goal. The mathematics of weight control are simple:
1) To keep your weight at its current level, you should remain at your daily caloric
maintenance level.
2) To lose weight, you need to create a calorie deficit by reducing your calories slightly
below your maintenance level (or keeping your calories the same and increasing your
activity above your current level).
3) To gain lean body weight, you must increase your calories above your maintenance
level (and engage in a program of progressive resistance training).
How to adjust your calories for fat loss
Now let’s talk about how many calories you should eat to lose body fat. A calorie
deficit that’s too large or maintained for too long, will eventually invoke the starvation
response and slow your metabolism. Nevertheless, you must have a calorie deficit if you
want to lose fat. The secret is to use a small calorie reduction and to avoid any diet that
calls for extremely large calorie reductions.
Body fat is nothing more than stored energy. To release stored energy, you must
be in a calorie deficient state. Calories not only count, they are the most important factor
in a fat loss program. If you are eating more calories than you burn, you will not lose fat,
no matter what you’re eating or what kind of training you’re doing. Some foods may get
stored as fat more easily than others because of the way they affect your hormones and
blood sugar, but always bear in mind that too much of anything will get stored as fat. You
can never override the laws of energy balance.
There are 3500 calories in a pound of stored body fat. In theory, if you create a
3500-calorie deficit per week through diet, exercise or a combination of both, you will
lose one pound. If you create a 7000 calorie deficit in a week you will lose two pounds.
The calorie deficit can be created through diet, exercise or preferably with a combination
of both. Because we already factored in the exercise deficit by using an activity
multiplier, the deficit we are concerned with here is the dietary deficit.
The strictly mathematical model of calories in versus calories out doesn’t always
work because of the body’s weight regulating mechanism – also known as the starvation
response. Nevertheless, the mathematical model gives you a starting point, and as long as
you follow the 8 strategies you learned in chapter two for avoiding the starvation mode,
you will continue to get steady, predictable fat loss by using a small, temporary calorie
deficit in conjunction with aerobic exercise and weight training.