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How many calories do you need?

You probably know what calories are.  The energy in food.  Or, as I’ve seen it defined, a little monster that sneaks into your closet and shrinks all of your clothes.  But how many calories do you need each day?

In the nutrition world, we use an equation known as the Mifflin-St. Jeor.  This calculates the number of calories you need at rest, your Resting Metabolic Rate (RMR).  So the amount of calories you would need just to sit around all day.

To use this equation, you’ll need to convert your height and weight to metric units (ugh America y u no use metric?!).  Don’t worry, it’s not so hard.

Your weight divided by 2.2 = your weight in kilograms
155 lbs / 2.2 = 70.4 kg
Your height in inches multiplied by 2.54 = your height in centimeters
66 inches x 2.54 = 167.6 in

Then plug your metric height and weight into the Mifflin-St. Jeor equation.

(RMR) calories/day: (males) = [10 x weight (kg)] + [6.25 x height (cm)] – [4.92 x age (years)] + 5
(RMR) calories/day: (females) = [10 x weight (kg)] +[ 6.25 x height (cm]) – [4.92 x age (years)] – 161

So for me:

[10 x 70.4 kg] + [6.25 x 167.6] – [4.92 x 22] – 161
704 + 1047 – 108 – 161 = 1,482 calories (kcals)

Now you might be thinking that sounds pretty low.  But remember, this is ONLY the energy I would need at rest.  So sitting all my duff all day, not doing anything, this would be how many calories I would need.

But of course, I am doing things during the day.  I dance around my apartment, walk from my bed to the kitchen and back to my bed, and I even think about going for a jog!  So how can we factor in the energy we use in our daily activities?

Well, an Activity Factor of course!  From the list below, find the activity level that best matches you, then multiply that Activity Factor by what you calculated your Resting Metabolic Rate to be.\

  • 1.200 = Sedentary (little to no exercise)
  • 1.375 = Light Activity (light exercise about 20 minutes, 1-3 times/week)
  • 1.550 = Moderate Activity (moderate exercise 30-60 minutes, 4-5 times/week)
  • 1.725 = Very Active (heavy exercise over 60 minutes, 6-7 times/week)
  • 1.900 = Extremely Active (athletes who train many hours/day or extremely physically demanding job)

So on a good day, I’ll need 1,482 calories x 1.55 = 2,297 calories.

In total, the amount of calories you need every day is your RMR x Activity Factor.  Eating this amount of calories will cause you to maintain your current weight.  So what happens if you want to lose or gain weight?  Well you just add or subtract from that number!  Though this is debatable, generally 1 lb = 3,500 calories.  Therefore, if you want to lose 1 pound in a week, create a deficit of 500 calories/day.  Instead of eating 2,297 calories/day, I would eat 1,797 calories/day to lose 1 lb/week!  Generally speaking, women should not go below 1,200 calories/day, and men should not go below 1,500 calories/day.

Calculate out your calorie needs!  Do you think you’re eating the right amount for your energy needs?  Write below with questions and comments!

Hi, I’m Sarah!

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