Relative Fat Mass (RFM): Comprehensive Guide

The question of which marker of obesity should be used by the primary care physician is still open. Skinfold calipers and hydrostatic weighing are among the many ways to measure body fat. However, the Body Mass Index (BMI) is the most commonly used way to measure body fat.

Body Fat Mass: A Vital Human Component

Your body needs fat! It's an essential component that serves a variety of purposes. Its main job is energy storage, but it also has other important roles. For instance, it protects your internal organs and produces hormones, like leptin.

It is generally understood that the percentage of body fat in people varies according to age and sex. It is often observed that women tend to have a greater body fat percentage than men, which may be attributed to differences in reproductive and hormonal functions. Similarly, older people often have a higher body fat percentage.

While a certain amount of body fat is essential for human health, it is also important to be aware that excessive adipose tissue may not be as beneficial for human health as we would like. Research indicates that a high body fat percentage may be associated with an increased risk of morbidity and mortality. Consequently, the state of excessive accumulation of body fat is currently classified as a disease — obesity.

In view of this, a series of straightforward mathematical formulas were developed with a view to enabling people to calculate their body fat.

How to Calculate Relative Fat Mass (RFM)?

One of the best things about using RFM to measure body fat is how simple it is. You just need two things:

A simple tape measure, and
A basic formula

First, please take a tape measure and note your height and waist measurements. For optimal results, take the tape measure to just above the top of your hip bone and wrap it around your body. Please ensure that your measuring numbers are consistent (inches or centimeters). Once you have the number, it's really simple! Just put it into this simple formula:

For men: 64 – (20 x height/waist circumference)
For women: 76 – (20 x height/waist circumference)

RFM Calculator – A practical example

Let’s use a practical example to show you how to calculate your fat mass. We will calculate the relative mass of Lindsay, who is 170 cm tall and has a waist circumference of 70 cm.

RFM = 76 - 20*17070 = 27.5

So, Lindsay’s relative mass is equal to 27.5%

Why is RFM Important?

One of the key limitations of BMI is its inability to differentiate between fat mass and non-fat mass. According to Cedars-Sinai healthcare professionals, approximately 60% of women and 13% of men are misclassified when BMI is used to determine if someone falls into the "obese" category. This highlights the lack of precision in the measurement. However, this changed in 2018 with the development the RFM, a more accurate method for measuring body fat.

Comparison of RFM and BMI

Metric	BMI	RFM
Formula	A set of scales and tape a measure	Simple (a tape measure only)
Assesses	Overweight and obesity	Complementary toll to assessing body composition.
Accuracy	Less accurate (classifies people into underweight, normal, and overweight).	More accurate in detecting excess body fat in non-obese objects
Health Risks	Breathing problems, gallstones, and certain cancers.	Overweight patients facing diabetes, high blood pressure, and heart diseases.

Compared to gold standard methods (DXA/BIA), DEXA, (dual-energy x-ray absorptiometry) scans, RFM provides consistent results.

Health risks associated with high levels of RFM

Relative fat mass predicted hypertension in women and diabetes for both sexes.
RFM is a reliable measure for identifying older individuals at increased cardiovascular risk ScienceDirect.
Compared to BMI, RFM is shown to be better at predicting metabolic syndrome PMC.

Ideal RFM Ranges for Men and Women

Using a standard developed by the American Council on Exercise, the ideal RFM for men and women is the following:

Classification	Females (% fat)	Males (% fat)
Essential fat	10-13%	2-5%
Athletes	14-20%	6-13%
Fitness	21-24%	14-17%
Average	25-31%	18-24%
Obese	32% and higher	25% and higher

How to Keep Your RFM at a Healthy Level?

It's so important to take care of yourself if you want to keep your body fat ratio healthy and avoid diabetes and heart disease. The best way to do this is to make sure you're eating well and getting enough exercise every day.