BMI v. Body Fat: What’s the difference and how can you measure it?

There are a lot of terms and numbers thrown at you when you are trying to understand your body composition.  Here is a short and easy guide on BMI, Body fat, and the many ways you can measure it.

What is BMI?  
BMI refers to your Body Mass Index.  You can calculate BMI and find your general fitness category here.  It is a ratio of your height to your weight, and in a way can be completely unrelated to your body fat, based on your muscle composition.  Here is how:  Imagine a 5’7″ woman who weighs 160 lbs.  That puts her in the “overweight” category.  However, you find out she is actually a competitive weightlifter, with a large amount of muscle mass, and little actually body fat.  BMI does not differentiate between fat and muscle.

What is Body Fat?   
When fitness professionals refer to body fat, they are referring to subcutaneous fat, that is the fat that sits directly under the skin.  Having excess subcutaneous fat can become problematic for your health, especially if most of that fat is located around the midsection, around your vital organs.  Body fat can be measured many different ways, and they all have their pro’s and con’s.  Further, every method isn’t 100 percent accurate, so it is best to look at your body fat measurement as more of an estimate.

Here is a list of all of the different ways body fat can be measured.  I have included my own measures from each method, just to show you how numbers can vary even in the same person across methods.

1) Skin fold measurement:  This test estimates subcutaneous body fat by measuring folds of skin at various anatomical locations.

Pros: inexpensive, quick, easy.
Cons: You are literally having your fat pinched.
Accuracy: +/- 3.5%
My Measurement: 16.8%  for the 7-site measurement

2) Bioelectrical Impedance Analysis:  This test runs a low electrical current through either your feet or your hands (depending on which machine you use) to estimate body fat.  The faster the current is able to go, the lower it assumes your body fat to be.   

Pros: Portable, inexpensive, easy, quick.
Cons: Highly variable based on hydration, time of day, women’s menstrual cycle, etc.
Accuracy: +/- 8%
My Measurement: 17% through hands, 19.5% through feet.

3) Underwater weighing/Hydrodensitometry:  This measure is considered the gold standard for exercise professionals.  The idea is that fat weighs less in water (it floats!), so the difference between your land weight and underwater weight can give you an estimate of your body fat percentage.fat3

Pros: Most accurate
Cons: requires special equipment, estimates lung volumes, difficult to perform (you have to completely submerge yourself and blow all of the air out of your lungs – then hold it for a few seconds)
Accuracy: +/- 3%
My Measurement: 14.6%

4) Bod Pod/air displacement plethysmography: This method uses the same idea as underwater displacement, but with air in a an oval “pod” that you sit in.
Pros: Easy, fairly accurate
Cons: expensive, special equipment, some people may not fit/will become claustrophobic.
Accuracy: +/- 3.4%

5) DEXA (Dual-energy X-ray absorptiometry): Dexa uses low dose x-rays to measure body fat as well as bone density.  This method is accurate, but you only get a 2D representation, so some professionals question its accuracy.

Pros: Accurate, easy, you also get bone density information.
Cons: Expensive, special equipment, radiation, and some people may not fit on the table.
Accuracy: +/- 1.6%
My Measurement: 21%

Take Home Message:
Every method has its pro’s and con’s, and not one method is 100% accurate (notice, my numbers ranged from 14-21%, thats a pretty big difference!).  If you have the opportunity to have your body fat measured, go for it, and look at is as an estimate.  Try and do it first thing in the morning in a fasted state, and stay consistent in that every time you get re-measured; that way will give you the best idea of how much fat you have lost, rather than water weight or daily fluctuation.  Otherwise, know its just another number, and try to go off of how you feel and how your clothes fit.

Happy Thursday!

-Juliane, ACSM CEP

Workout Wednesday Circuit

I did this circuit with a friend the other day and I loved it, so I thought I would share! This circuit involves 4 exercises, that you will do for 16, 14, 12, 10, 8, and 6 reps. Try to get through the full circuit, and then take a minute or two for some water before beginning the next round. You will need a weight.

1) Dumbbell Squat and Press: Remember to keep good form – neutral back and neck, and sit back without letting knees fall over the toes.

2) Dumbbell Pushup: (Split your reps evenly on each arm, for instance if you are on your first round, do 8 on the right side and 8 on the left side).


3) Mountain Climbers: Be sure to keep core tight and engaged for this one.


4) Turkish Get Ups: Same as the push-ups, split your reps on each side, and return to start the same way you got up.  If a weight is too much, try doing these unloaded first.


Let me know what you think!

happy circuit training!

-Juliane, ACSM CEP

Easy No-Bake Cereal Bars

This recipe does require some heat, but its very very easy to make!  These bars are high energy snacks, great for bringing hiking, to the beach, or as a filling breakfast on the go!

Step 1: Gather the ingredients.  

  • 2 cups peanut butter (don’t get the all natural kind that separates, get the standard Peter Pan or Skippy.
  • 1.5 cups honey 
  • 2 of your favorite cereals
  • At least 2 fillings (nuts, chocolate chips, sunflower seeds, dried fruit, anything you want)
  • Sprinkle of salt

Step 2: Add the peanut butter and honey to a small pot over medium heat.


Step 3: While that is melting, gather your cereals.  I choose two different flavors of Chex, because the boyfriend has Celiac disease, so we have a gluten free kitchen.  You can really choose anything, OR sub one of the cereals for dry oats.  In a 9X12 pan, mix 4 cups of Cereal 1 and 4 cups of Cereal 2 in the pan:


Once you come back to your peanut butter and honey, it should look like this:


Step 4: Give it a stir, and pour it over the cereal mix under every piece is coated.  It won’t seem like enough at first, but don’t worry, it is.


Step 5: Add your fillings.  I used whole walnuts


And chocolate covered raisins:


Press down into the pan until the top is completely flat, and refrigerate over night.  In the morning, sprinkle just a little bit of salt on top to cut the sweetness and give it a sweet & salty flavor.  All done!

Let me know what you think of these!

Happy snacking!

-Juliane, ACSM CEP