Fitness Series: How to calculate calories

As promised, the first blog post in my fitness series will be calculating your daily caloric intake.  In order to  lose or gain weight you need to make sure you are eating the right amount of calories for your metabolic needs.  If your goal is to lose weight, you will need to be at a caloric deficit, if you want to gain weight you need to be at a caloric surplus.  Continue reading below for a detailed explanation on how to calculate your personal caloric needs.

The first thing you will need to do is calculate your Total Daily Energy Expenditure (TDEE)- this is the total number of calories your body uses in 24 hours.

To calculate your TDEE you will need to calculate your Basal Metabolic Rate (BMR)- this is the minimum calorific requirement needed to sustain life in a resting individual.

BMR can be calculated with two different equations. One provides a more accurate number than the  other,  but there is no great statistical difference.

The first formula is the Harris Benedict Formula-which uses your total body weight:

BMR MEN= 66 + (13.7 X wt in kg) + (5 X ht in cm) – (6.8 X age in yrs)

BMR Women= 655 + (9.6 X wt in kg) + (1.8 X ht in cm) – (4.7 X age in yrs)

2.54 cm= 1in

2.2lbs = 1 kg

To demonstrate an example I will use a 24 yr old female who weighs 136 lbs and whose height is 5ft 0in.

BMR Women= 655 + (9.6 X 61.82 kg) + (1.8 X 152.4 cm ) – (4.7 X 24 yrs)
BMR Women=655 + (593.47) + (274.32) – (112.8)
BMR Women=1,409.99 calories

The second formula is the Katch-McArdle formula-which uses your lean body mass:

BMR (Men and Women)= 370 + (21.6 X lean body mass in kg)

To demonstrate an example I will use a female whose lean body mass is  101 (45.9 in kg).

BMR = 370 + (21.6 X 45.9)

BMR = 1, 361

As you can see the difference between the two calculations is about 49 calories.  It is up to you which formula you prefer to use. I am going to use the number from the Katch-McArdle formula in this case.

Now that we have calculated our BMR, we can multiply it by an activity factor to obtain our TDEE.

Activity Factors:
Sedentary = BMR X 1.2 (little/no exercise, office job)
Lightly active = BMR X 1.375 (light exercise/ 1-3 days/wk)
Mod. active = BMR X 1.55 (moderate exercise/ 3-5 days/wk)
Very active = BMR X 1.725 (hard exercise/ 6-7 days/wk)
Extr. Active = BMR X 1.9 (hard daily exercise/sports & physical job or 2 X day training, marathons)

Our female is moderately active so her TDEE will be 1, 361 X 1.55  which = 2,109 calories/ day. 

So now we know, if our female wants to maintain her current weight she will need to consume 2,109 calories per day.

Lets say our female’s health goals are to lose weight, the recommended weight lose rate is 0.5lb – 2 lb per week In order to burn 1 lb of fat you need to burn 3, 500 calories.  For our female to meet this 1 lb/week goal, she would need to subtract 500 (20-30% reduction) calories from her TDEE.

Thus our female would need to consume 1, 609 calories per day if she wanted to lose 1 lb of fat per week.  It is recommended that you not exceed a deficit of 700 calories per day, which would amount to  2 lbs of fat loss per week.

On the other hand, if our female’s fitness goals were to gain weight (muscle mass),  she would need to add an extra 500 calories to her diet. Thus her daily caloric intake would be 2, 609 calories/ day.

Please keep in mind that you should recalculate your caloric intake after every 5 lbs lost.

Now it is not enough to just make sure you are eating the right amount of calories.  These calories need to come from the right types of foods (i.e. clean whole foods).  In the next part of my fitness series, I will demonstrate how to calculate proper macro nutrient amounts for gaining/losing weight.

Disclaimer: I am not a certified trainer or nutritionist. Please check with your doctor prior to starting any diet or exercise plan.  The information provided above is what I have learned via personal research.



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