Monday, July 7, 2014

Crash Course: Calculating Your Body's Needs

As a dietetics student, I am often struck with questions like:
"How many calories should I eat each day?"
"How much protein do I need? Am I getting enough?"
Here is the simple answer for you: Everybody is different! One of the aspects of nutrition that has been emphasized the most in my classes is that nutrition is a very personalized science. Your nutrient needs very much depend on your body. In fact, dietetics students are now required to take a genetics course in college because we may move towards using your genetic makeup to determine your nutrition needs, in the future. Therefore, nutrition is really not a "one size fits all" approach. That is one reason why I am so passionate about going into the field of nutrition counseling, so I can sit down with people one-on-one and develop a plan just for them.

So now you are probably wondering how the heck you figure out how much you do need of all of those macronutrients. There are apps that you can download that will help crunch the numbers for you,
however, if you are like me, you kind of like to see how you get the final recommendations. Or if you are a dietetics student and you stumble upon this blog post, this may be a good review for you as well. (We all need a little basic review time!) I wish I would have had a handy guide like this prior to my practicum!

Let me break it down for you! Here are the formulas I used with many of the clients I saw during my practicum experience last summer.

Pounds to Kilograms Conversion
Before we get started, I want to mention that many of the calculations are done in the metric system. Therefore, you probably aren't familiar with your weight in kilograms. However the conversion to pounds is simple! Just divide your weight in pounds by 2.2 and you will come up with your kilograms weight.

For example, a 130 lb woman would weigh 59 kg (rounded). (130lb/2.2=59.09kg).

*To make the rest of the calculations easier, I will use the same female data to come up with her nutrition profile. 

Body Mass Index Calculation
Before I do any of the macronutrient calculations, I always calculate a person's BMI (body mass index). There has been much debate on the accuracy of BMI in depicting the health of a person, however it is the quickest measure when a dietitian is making these calculations and placing a patient into the weight categories below:1
 The equation is:1

Weight (kg) / [height (m)]2      (or, as I prefer...)

 Weight (lb) / [height (in)]2 * 703
I also like to use the calcuator that the CDC provides.

130 lb female at 5'5"

130 lb / [65 inches]2 =21.6
The female in this example has a BMI of 21.6 and would be categorized in the "normal" weight status. Therefore, you would proceed on with the rest of the calculations.

However what if you are overweight or obese?

180 lb female at 5'5"
180 lb / [65 inches]2 =30
The female is classified as obese. Since her ultimate goal is to lose weight, we are going to need to adjust her body weight for the rest of the the formulas by first using the Hamwi method to determine ideal body weight.
1.) Determine Ideal bodyweight (Hamwi Method)
a.       Women: 100+5 lbs. for each inch over 60 inches
                                                               i.      Ex. 5’5” = 125
b.      Males: 106+6 lbs. for each inch over 60 inches
2.) Subtract IBW from current weight
                                                               i.      Ex: 180-125=55lbs difference
3.) Take the difference and multiply by 0.25
                                                               i.      Ex: 55*0.25=13.75lbs (can round to 14 lbs)
4.) Take IBW and add amount from step 3
                                                               i.      Ex: 125+14lbs=139
1.       Use this number for energy needs (Adjusted Body Weight—ABW)

Women with a BMI between 19-27 are recommended to consume 25-27 kcals/kg of body weight (adjusted for breastfeeding.) Men with a BMI between 19-27 are recommended to consume 25-28 kcals/kg of bodyweight. There are a number of methods used to calculate energy needs, however this is probably the most simple form. If we were dealing with bed-ridden hospital patients, our approach would change.

For example:
The 130 lb (59kg) woman should consume 25-27kcals * 59kg = 1475-1593 kcals per day. 
This range will generally be rounded (1500-1600kcals) and is adjusted if the person is physically active. This is just a basic example. 

For carbohydrates, I don't follow any equations. Rather, I follow the RDA (Recommended Daily Allowance) and recommend 130 g per day for adults.2

The recommendation is to consume 0.8 gram of protein/kg of a person's body weight.2 However, during my practicum, I shadowed a registered dietitian with years of experience and she recommended that RD's use 1.0 gram when making calculations. Whichever you choose, it probably won't make a world of difference.

For example:
The 130 lb (59kg) woman would need 59kg * 0.8g=47g, rounded (or 59 g, if using the 1 gram method).

The recommendation is that a person consume 30 cc/kg of body weight. (This number will increase if you are breastfeeding or engaging in exercise). {30cc =1.014 ounces}

For example:
The 130 lb (59 kg) woman would need 59kg * 30 cc=1770cc (about 60 ounces)

I hope this is was helpful to future dietitians (like myself) and those out there who are simply curious about how to calculate their nutritional needs. If you would like me to do do all of the calculations for you, just send me an email! ( I am always looking for practice!

  1. Centers for Disease Control and Prevention. About BMI for adults. September 2011. Accessed July 7, 2014. Retrieved from:
  2. Mahan K, Escott-Stump S, eds. Krause's Food, Nutrition, and Diet Therapy. 12th ed. Philadelphia, PA: WB Saunders; 2008.


  1. This is so helpful! I definitely used this for my calculations!

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  3. This greatly helped me make my diet plan just the way my body needs the diet to be! I even shared my experience on and people are loving it there too! This was some amazingly helpful work and am very thankful to you for sharing it with us!