Q:  What is the difference between body mass index (BMI) and body fat percent?
I am approximately 20% BMI, at 5'1" and 110 lbs.  But, according to a scale that measures body fat percent, I am 26% which sounds terrible to me but probably because I'm thinking in terms of BMI.
-Linda

A:  Hi Linda,
Great question and thank you for taking the time to write!  Your exact BMI for your height and weight is 20.8. The healthy BMI range for you is 18.5 to 24.9 so you are right in there and very healthy according to a BMI measurement.
What Is Adult BMI?
Body Mass Index, or BMI, is based on your height and weight.  Doctors often use BMI to determine if a person is underweight, at a healthy weight, or is overweight.

While BMI is accurate for most people, it doesn’t work for everyone.  That's why other tests should be taken as well and your body composition/fat test is a smart second test, Linda.

Body composition is simply the ratio of lean body mass to fat body mass.  Too much fat can lead to health problems like heart disease, diabetes, high cholesterol and other serious conditions.  If you keep your body fat within a reasonable level, you'll be healthier and, of course, slimmer.
For women, a body fat of 10-12% is essential, 14-20% is considered a healthy range for athletes, 21-24% is healthy for fitness, 25-31% is considered an “acceptable” range and anything above 32% is considered obese. 

So Linda, if your scale measures 26% that is a bit high.
I am curious, what scale do you have?  Many scales out there are bio-impedance scales; they tend to be very inaccurate and have an error ration of -5 to 8%.  The best way to test your body fat is the Hydrostatic Method. But this is @ a lab weighing you under water, so it’s not the easiest way, but definitely the gold standard with an error ratio of only 1.5 %.  This could be fun to do one day if you really want to know exactly where you stand.

I think it's best to take your body fat again and make sure it's first thing in the morning and don't drink anything before, OK?  Also, write down what you ate the night before.  Now, take this measurement as a call to action to workout and eat better, but not a label of "Oh my gosh, I am fat!".  Don't focus on the number!

Try to work out and eat healthy and don't get on that scale again for two weeks, OK?  Just put it away.  After two weeks, measure again and repeat the exact circumstances before your first test.  Same time in the morning and same liquids. Also, remember the meal the night before, and unless it was really unhealthy have the same type of foods.

Note:  Salt can also throw the numbers off as well.  Even your body temperature can, so really try create the same conditions before each test.

Now this measurement should be true value!  You need to focus on the movement of body fat, plus or minus, not the number.  If your dropped 2% that would be great.  Remember, you lost two % not the actual overall number because it's probably not accurate.

Repeat this cycle until you feel good with where you’re at and how feel.  Then decide to maybe get a proper test or not.

Remember it's simply a measurement and motivator.

All the best to you Linda!

All the best in Health everyone !

Full entry | posted by Gregory Joujon-Roche in Community Questions
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