Demystifying calorie math

FACT: Weight loss or gain is dependent on calories in vs. calories out.

Let’s elaborate on that statement.  If you want to lose weight, you need to expend more calories than you take in, and vice versa to gain weight.  It is all just math.

So, how to determine whether your calories are net positive or negative?  The easiest way over the long term is to keep a consistent intake and simply see if you gain, lose, or maintain your weight.  However, if you want to be more exact and be able to track calories on a daily or weekly basis to make the change more manageable, you could use one of the following formulas to get a decent estimate of what you burn in a day.

The information about yourself you will need consists of: body weight (in kg), height (in cm), and age (in yrs).  Plug those numbers into this formula for your basal metabolic rate (how much energy you expend at rest).  Because the formula is sex specific the letter “S” means add 5 to the total if you are male or subtract 161 from the total if you are female.

Calories Burned = [(10.0*weight)+(6.25*height)-(5.0*age)] + S

As an example, I am 69kg, 168cm, 30yrs old, and female.  My basal metabolic rate would be 1,429 kcal burned at rest per day.

If you happen to have had your body fat measurements taken and know your amount of lean mass, you would be able to plug that number into a different formula to calculate your resting metabolic rate.  Resting and basal metabolic rates, for everyday purposes, are the same basic concept.  Use this formula with your lean body mass:

Calories Burned = 500 + (22*lean body mass in kg)

These numbers are useful because they give you an approximate starting point for the number of calories you burn each day.  The number only accounts for when you are at rest, so you would need to add in more calories for any activities throughout the day (walking, reading, lifting weights, driving, shopping, swimming, carrying your 9 month old, etc).  There is a method for figuring out estimates for all daily activities, but it is rather tedious.  With these baseline numbers you can at least start figuring by trial and error how many more calories beyond the baseline are appropriate to help you achieve your specific weight goal (to gain or to lose).  Remember, a pound is worth 3500 calories, so a difference (plus or minus) of 500 calories a day would equal a pound a week.

Later on we will talk about figuring out how the calories for the day should be divided for specific goals!