Eat Right Around Chicago

Get a Clue About Calories

USA Today reported that Americans do not know how many calories they need per day in an article titled, Many Americans Clueless of How Many Calories They Do or Should Eat.  While I find the findings of the study interesting, I thought that if I didn't know how many calories I needed, I'd want to know now!  And not just the average range based on my age and gender.  So, yay!  I have a blog and I can answer this question for you and provide you some options. 

Note:  I'm not saying that you should count calories, but when faced with a food label, it is nice to have a point of reference.    

How Many Calories Do You Need?

Calorimetry is the measurement of energy expenditure (or calorie needs).  There are many ways that you can estimate your calorie needs - some more painful (math) than others.  Here are your options (starting with the most inconvenient, but most accurate):

1.  Find a lab (like at a University).  The most accurate way to assess how many calories you need is through laboratory testing using indirect calorimetry.  This measures the rate of oxygen consumption and carbon dioxide production.  Basically, you have a mouthpiece and a nose plug and you breathe into a machine that is called a metabolic cart.  It tells you your metabolic rate (how many calories you need).  It's simple, but it's not likely in your living room.

2.  Find a fitness club or wellness center.  Look for an establishment that employs registered dietitians or ACSM certified personal trainers or exercise physiologists that own a handheld calorimeter.  You breathe into these as well, but they fit in your purse and they are a bit less accurate. 

3.  Get a calculator.  There are prediction equations that you can use to estimate the number of calories you need.  They are pretty good, meaning that they are valid, but kind of a pain because they involve math and it's always difficult to estimate your activity level. They will give you the amount of calories you need at REST.  It's just the calories to sustain your life and hang around the house, but not to support exercise or activity like walking the dog or tap dancing.  Check your work and make sure your number falls somewhere between 900 and 3500.  If you get 55,000 calories, then you made an error.  And let's hope that I didn't make a typo because then you'll really be confused!   There are a few to choose from (named after the researcher who came up with them):  

A = age in years
H = height in cm (more math...inches X 2.54 = cm)
W = weight in kg (again...pounds / 2.2 = kg)

Shofield equation:

calories at rest = 48W - 0.11H + 3670

calories at rest = 34W + 0.06H + 3530

Harris-Benedict equation: 

calories at rest = (66 + 13.8W + 5H - 6.8A) X 4.18

calories at rest = (655 + 9.5W + 1.9H - 4.7A) X 4.18

Mifflin equation:

calories at rest = 5 + 10W + 6.25H - 5A

calories at rest = -161 + 10W + 6.25H - 5A

4.  Consider your exercise/activity level.  This is where the buck stops for many because it is difficult to estimate your activity throughout the day.  You can estimate your activity level using an activity factor (below) or you can find a table or calculator online (which is what I recommend).  I like this one by ProHealth, and Health-Calc is fun, but you can use any of them really.  Most of them use something called METS (metabolic equivalents) to estimate the number of calories you expended during a given activity and should ask for your weight and time spent exercising.  

To come up with your own activity factor (since you have a calculator out already), you will be considering the number of hours you are at rest or engaged in very light or heavy activity:

Rest:  Hours X 1.0 =
Very Light:  Hours X 1.5 =
Heavy:  Hours X 7.0 =

Average activity factor:  add all these up and divide by 24 hours. 

Take this number and estimate total energy needs:

Resting calories X Activity factor = Total Energy Needs

5.  Do the quick and dirty.  Are you really going to count calories?  If not and you just want an estimate, here you go! 

Want to lose weight:  25 calories X Weight in KG
Want to stay the same:  30 calories X Weight in KG
You're active:  35 calories X Weight in KG
Want to gain:  40-45 calories X Weight in KG

Done.  Now America is no longer clueless about calories.  





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1 Comment

Tom said:

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I like the quick and dirty. I tried the hard math ones several times and kept coming up with numbers between 5000 and 7000 and one that was like 1800. Hmmm...

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