While DEXA scans (Dual Energy X-ray Absorptiometry) are intended to measure bone mineral density, they also provide an accurate estimate of body fat percentage but not everyone wants to- or is able to go for this kind of testing to determine how much body fat they have. While most gyms and many pharmacies often have handheld impedance body fat analyzers, these can be affected greatly by changes in body water status, as can high tech digital bathroom scales that have body fat analyzers built in.
Determining Body Fat Percentage based on BMI
Body Mass Index (BMI), which is body mass divided by the square of body height is often used to determine whether someone is normal weight, overweight or obese despite the fact that it is limited in its ability to estimate body fat percentage due to misclassification of body fat-defined obesity. For example, a BMI ≥30 which indicates obesity overlooks nearly 50% of women who have a body fat percentage > 35% which the cutoff for obesity. The US Third National Health and Nutrition Examination Survey estimated the diagnostic accuracy of BMI for body fat-defined obesity at 94% for women and 82% for men [1].
The body fat percentage chart below from the American Council on Exercise (ACE) is a commonly used by trainers and gyms to determine body fat percentage but is limited since it is based on BMI.
Determining Body Fat Percentage Based on Anthropometrics
There are a number of equations based on body measurements (anthropometrics) that have been proposed as alternatives to BMI to better estimate whole body fat percentage. Some require more than 10 different measurements, others require up to 4 different skin-fold measurements using calipers and even others are complex equations using multiple measurements. The common problem amongst all of the existing equations is a lack of simplicity, limiting their use in routine Dietetic or medical practice.
Determining Body Fat Percentage Using Relative Fat Mass (RFM)
A recently published study systematically explored more than 350 anthropometric measurements with the aim of identifying a simple linear equation that is more accurate than BMI at estimating whole body fat percentage in both men and women.
The equation is amazingly simple;
Relative Fat Mass (RFM): 64−(20í—(height/waist))+(12í—sex),where sex = 0 for men and 1 for women.
Click here for an article on how to accurately measure your waist circumference for use in this equation.
Compared with BMI, the Relative Fat Mass (RFM) equation was more accurate for body fat-defined obesity among both men and women over 20 years old and RFM was more accurate than BMI for those with a high body fat percentage and this accuracy held for those that were Mexican-Americans, European Americans and Africans-Americans.
Looking at the equations another way, Relative Fat Mass (RFM) in both metric and American measurements is;
Relative Fat Mass (RFM):
Men: 64 — (20 x height/waist circumference)
Women: 76 — (20 x height/waist circumference)
How to Interpret Relative Fat Mass Results
Based on the research of Gallagher et al and data from the World Health Organization, health body fat ranges have been determined as follows;
In the case of Example 1, the 41 year old male with an RFM of 32.2 would be considered at the low end of “obese”.
The 60 year old female of Example 2 with an RFM of 38.9 would be classified at the low end of “overfat”.
The 50 year old female of Example 3 with an RFM of 33.4 would be classified at the higher end of the “healthy” range.
Some Final Thoughts…
Obesity is an significant risk factor for multiple chronic diseases and conditions including Diabetes, coronary artery disease, hypertension (high blood pressure) and certain types of cancer [1].
This new and very simple equation accurately estimates whole body fat percentage enable individuals to easily calculate whether they are have increased weight to lose and will enable clinicians to help their patients achieve optimal weight and waist circumference.
If you want to learn how to eat well and lose weight and inches and achieve a healthy body weight and waist circumference, I can help. I offer a number of services and packages that can be taken in-person in my Coquitlam (British Columbia office) or via Distance Consultation (Skype, long distance telephone). You can click on the Services to learn more or have a look around the Shop. Please feel free to send me a note using the Contact Me form on the tab above if you have questions and I will reply as soon as possible.
To your good health!
Joy
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References
Woolcott OO, Bergman RN. Relative fat mass (RFM) as a new estimator of whole-body fat percentage ─ a cross-sectional study in American adult individuals, Scientific Reports; Volume 8, Article number: 10980 (2018), https://www.nature.com/articles/s41598-018-29362-1
Gallagher, D. et al. Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. Am J Clin
Nutr 72, 694—701 (2000).