BODY FAT VS. BODY MASS INDEX

Chgogal1

How is it that whenever I get my body fat measured, it is anywhere between 28% to 30%; (obese) however my BMI is a healthy 21%. I am 5'2 - small frame and weigh 117 lbs. I am approximately 5 lbs heavier than, I would ideally like to be, (a little extra weight in my tummy); however, by no means am I considered obese. I just am very skeptical of these body fat figures. I really do not think they are very accurate.

maureensm

According to the standard body fat percentage range (http://lowcarbdiets.about.com/library/blbodyfatcharts.htm), you're percentage is perfectly in the "healthy" range (21-33%). I think you were looking at the BMI range when comparing Body Fat % instead of Body Fat % profiles. They are different measurements. The healthy BMI range is 18-25. For both measurements, you are in the healthy range. Hope this helps.

maureensm

Actually, your range is 23-35%, which is even better. You look so young in your profile picture, I assumed you were in the 20-40 year category!

TrainingWithTonya

Body fat is much more accurate then body mass index. BMI is an index used for the masses to stratify risk of disease because it is easy to do and doesn't actually require any contact with the person being measured. Body fat is much more accurate on an individual basis because it quantifies fat mass and fat free mass. High fat mass increases risk for cardiovascular diseases, diabetes, atherosclerosis, stroke, cancer, etc., etc., etc. So, knowing your fat mass is much more beneficial then knowing how your weight compares to the square of your height, which is all BMI is. You can be a low weight and be a high % of fat. If you lose fat and build muscle, you can remain the same weight but be in a smaller size. Doing so will decrease your risk of all the above mentioned diseases.

My sister and I are a great example of this principle. I weight 40-50 pounds more then she does so I score as obese on the BMI charts. She, however, doesn't exercise and scores as healthy on the BMI charts. But her body fat is much higher then mine so when you look at us, you would think she weighed more. She is in a size 18-20, whereas I'm in an 8-10. Looking at our disease risk, she has high blood pressure already (she's only 35, and she's had it for 10 years) and is at a high risk of cardiovascular issues. I on the other hand have been tested by a cardiologist with electrocardiogram and echocardiogram and have been told I have the heart of an 18 year old (I'm 38 BTW), so I'll take my extra 50 pounds and be happy with it because I know my muscle and lack of high body fat is much healthier then her "healthy" reading on the BMI chart.

That being said, the accuracy of a body fat calculation can be questioned. Unless you have a trained professional measure your body fat, it's not going to be as accurate. Also, the formulas where you put your measurements in online are the least accurate way to do it yourself. If you are going to try and get an accurate measurement, I'd recommend a bio-electrical impedance machine for at home use. Thats the scales or the handheld. Know that the handheld will read a little low and the scale will read a little high. Neither will be accurate though, if you aren't well hydrated. So make sure you don't use one at home while dehydrated or during that time of the month. Body water level will throw them off quite a bit.

Chgogal1

Thank you both for your comments and information. However, I still am very skeptical about this whole body fat measuring. I kinda feel like the trainers at the health club just use it as a selling tool. Seems like from what I have read in the past is that the most accurate way to have your body fat measured is in a lab doing that underwater test.

emott84

You could always see if a doctor could do a body fat test, or someone else who is trained to do it but doesn't have any sort of sales quota to meet :P

Gyms try to sell their personal training packages at fitness consultations, so many of the consultants may be pushy or fudge the numbers a bit. I would hope that a reputable gym wouldn't do that and still give you the facts straight up, since many people can't afford the personal training! (I know at my gym that it's nearly 1000 bucks for 12 sessions! Um, no.)

TrainingWithTonya

Thank you both for your comments and information. However, I still am very skeptical about this whole body fat measuring. I kinda feel like the trainers at the health club just use it as a selling tool. Seems like from what I have read in the past is that the most accurate way to have your body fat measured is in a lab doing that underwater test.

Yes, hydrostatic weighting use to be the gold standard for body composition, but it has recently been replaced by DEXA scanning as what is considered the most accurate. It's basically a total body x-ray, though, and can be quite expensive in some places. So you have to weigh your options as to whether or not you want that exposure to the x-rays or spend that much money. The real keys to body composition is to use the chart that comes with the way you measure and not an online "standard" as there isn't a true standard in body composition because of the standard deviation of error from type to type of estimator, and just compare you to you using the same method of testing each time so you can see changes over time.

As for the trainer doing it as a selling tool, that's entirely possible. Not all gyms or trainers have a code of ethics they follow. Hell, depending on where you are, the trainer may not even be certified. The gym industry really needs to be regulated and trainers shouldn't be allowed to be called trainers without a set level of education. Unfortunately, that doesn't exist yet. So, at this point in time it is still possible for them to fudge the numbers if they use calipers or measurements to estimate your body fat %. If they did a bio-electrical impedance, it's less likely that the numbers were fudged, though. If you want, I'll be glad to give you the formulas for estimating body fat from measurements so you can do it yourself and see your estimate of body fat without having to have any special tools. I'll warn you though, it's a lot of math. :ohwell:

triben

underwater water body fat testing is the gold standard followed by caliper test by a trained and experienced professional the scales and and handheld devices are good for following a trend but can be very inaccurate.

How was your BF tested? usually the BF is more accurate and the BMI is high because BMI does not take into account lean body mass and can give you a number that is to high.

Based on your numbers your in the healthy range for both depending what charts you look at. 5 foot 2 and 117 makes you a BMI of 21 which is healthy. I will not comment on Body fat because I am not sure how accurate it is. The number is higher than expected for BMI and your hight weight ratio and I would suspect the analysis was not the most accurate. probably 2 to 3 percentage points off and as much as 5 to 7 if it is one of the electronic measurements.

If you are healthy, fit, and your clothes fit the way you want then don't worry about those numbers in an absolute sense.

one of the members had mentioned a physician measuring your BF but as a physician myself I can tell you most would not even know how to begin to take the measurements. Just find a person that has good calipers and is experienced in taking the measurements. You could pay 100 plus to get the Hydrostatic testing underwater if the exact number is very important.

Good luck

Chgogal1

Thank you TrainingwithTonya. I belong to Lifetime Fitness, and the trainers are all certified. If you can give me the formulas for estimating, that would be wonderful. I am curious to see if I come out with the same numbers. Thanks again.

Chgogal1

Thanks triben. I was hoping to get input from a physician. What is your specialty. I am not overly concerned about the body fat numbers, since they can tend to vary so much depending on the method used to measure and the person doing the measuring.

TrainingWithTonya

Thank you TrainingwithTonya. I belong to Lifetime Fitness, and the trainers are all certified. If you can give me the formulas for estimating, that would be wonderful. I am curious to see if I come out with the same numbers. Thanks again.

It's been a while since I was in a Lifetime Fitness because we don't have them around here. Do they still use calipers? If so, I wouldn't trust it. It takes years to get really good at doing caliper measurements and most trainers, even certified trainers, don't have that practice in comparing their measurements with lab tests. If they get muscle in the pinch with the fat you will get a drastically high number. If you can get them to give you a copy of the actual site measurements, though, I'll give you the ACSM formulas for determining body fat from those, but there are multiple options based on what sites they used for the skinfolds. They should use either 3 or 7 sites for skinfolds. If they used less then that, their formula is useless. What I'm giving you now are the ACE formulas for determining body fat from circumference measurements. You will have to determine Body Density first and then use the body density to determine body fat %.


ACE Formulas for Determining Body Density from Circumference Measurements

Body Density for Women = 1.168297 - (0.002824 x abdominal in centimeters) + (0.0000122098 x abdominal in centimeters squared) - (0.000733128 x hips in centimeters) + (0.000510477 x height in centimeters) - (0.000216161 x age)

Body Density for Men = 1.21142 + (0.00085 x weight in kilograms) - (0.00050 x iliac circumference in centimeters) - (0.00061 x hips in centimeters) - (0.00138 x abdominal in centimeters)

Body Fat % = (495/Body Density) - 450

TrainingWithTonya

Sorry, I forgot to include the chart that ACE uses with those formulas, so here it is.

Women
Essential fat = 10-13%
Athletes = 14-20%
Fitness = 21-24%
Average = 25-31%
Obese = 32% or higher

Men
Essential fat = 2-5%
Athletes = 6-13%
Fitness = 14-17%
Average = 18-24%
Obese = 25% or higher

triben

I am a critical care physician and my undergrad was kinesiology. hope we were able to help.