Having a normal BMI Does Not Necessarily Mean That You Are Healthy

April 6, 2016

As a dietitian I’ve often had to “rely” on BMI to assess a person’s health. Although BMI may be an okay initial starting point, it can be a very inaccurate measure of a person’s health. According to a study from the Annals of Internal Medicine Relationship Among Body Fat Percentage, Body Mass Index and All-Cause Mortality, and my own experience assessing clients, a person can have a normal BMI but have a high body fat percentage. Conversely, I have seen many people with a high BMI but a healthy body fat percentage. This is because BMI only looks at height vs weight. BMI does not take into consideration very tall people, very short people bone density and people with a lot of muscle mass. In other words, it can be highly skewed, and should not be the only measure relied upon to determine a persons’s health status. Regardless of BMI, a high body fat percentage increases a person’s risk of mortality.  Inidividuals who were of normal weight but had high centralized body fat were at a much higher health risk than those with a high BMI and absence of high central body fat Normal-Weight Central Obesity
What are the healthy body fat percentages?
Men (average): 18-24% Women (average): 25-31%
Men (athletes): 6-13% Women (athletes): 14-20%
Essential fat is the percentage needed to sustain normal bodily functions and are:
Men: 2-5% Women: 10-13%
How to measure body fat percentage:
The most accurate way to measure body fat percentage is to get either hydrostatic weighing or a DEXA scan, both of which are very expensive.  The following are methods that are much more affordable and can be done on your own:
1. Skin Fold Caliper Test:
 This method is done by pinching your fat (skin fold) in designated areas and measuring with a body fat caliper which is then compared to a chart, listing age and gender, to determine your body fat percentage.  There are several different caliper testing methods, one that you can do on your own and measures one site, and others that measure up to 12 sites, and requires a skilled health professional to administer the test.
     Positives: When skilled at measuring, this test is accurate and dependable and something you can repeat frequently to track your body fat percentage.
     Negatives: The same exact spot needs to be used each time, or you could get variability in your results.  Measuring more spots will likely increase accuracy but will require a health professional who knows how to administer the test.  For people who are 35+ pounds overweight, the caliper may not be able to fit the skin fold.
2. Bioelectrical Impedance Analysis (BIA)
This device, in either scale or hand-held form, sends a small electrical current through your body (this is painless).  Muscle holds more water than fat, and so will conduct the electrical current much better than fat.  The strength of the electrical impedance along with height and weight metrics are used by the device to determine your body fat percentage.
       Positives: Very easy to administer and inexpensive. A great test for those unable to use the body fat calipers.
       Negatives: The test can be skewed by how hydrated you are.  For those with low body fat, this test is pretty inaccurate.  This test is a great place to start for those unable to use the calipers at first.
3. Anthropometric
This method uses body circumference measurements – usually neck, waist, hip and height – and is plugged into a formula to determine body fat percentage.  This is based on the US Navy Method.
    Positives: Easy to administer and cheap.
    Negatives: This test has questionable accuracy because body fat is not directly measured.  This is a good starting place if you do not have BIA or skin fold calipers.