If it were possible to remove all but the small amount of essential fat from your body and weigh what remained, you would discover your fat-free mass. The amount of fat on your body is commonly referred to as your body fat percentage, and the relationship between your body fat percentage and your fat-free mass is known as your body composition. Body fat percentage is much more important than your weight, as your weight can fluctuate day by day without the amount of fat on your body changing.
Components of Fat-Free Mass
Once all your fat has been accounted for, everything that remains is your fat-free mass. Fat-free mass consists of your bone, muscle and connective tissue plus your brain, skin, internal organs, blood, water and the chemicals stored within your body such as calcium, iron and glycogen. Two people of similar height who weigh exactly the same may have completely different fat-free mass values. A bodybuilder might weigh 200 pounds and be mostly muscle, whereas a couch potato may be 200 pounds of mostly fat. On a height to weight chart, these two examples would appear identical, but in reality, the bodybuilder's lower fat level means he is likely to be healthier.
Assessing Body Composition
Dissection may provide the most accurate way to separate fat mass from fat-free mass, but it's hardly convenient. There are, however, other less invasive ways to establish what percentage of your body is fat free and how much fat you are carrying. Tests include body composition assessment using calipers, hydrostatic or underwater weighing, bioelectrical impedance testing, magnetic resonance imaging or MRI, dual energy X-ray absorption or DEXA and predictions based on girth measurements. While no test is 100 percent accurate, DEXA and MRI scans are likely to be the most precise.
Your fat mass and fat-free mass are expressed as percentages with the two figures adding up to 100. If your body fat percentage is said to be 15 percent, your fat free mass is 85 percent. More often than not, the figure reported after a body composition assessment is your body fat percentage rather than your fat-free mass. For women, the optimal healthy body fat percentage is between 18 to 30 percent, but for men the figure is 10 to 25 percent. This is because women typically carry more fat than men for pregnancy and childbirth. Athletes can go as low as 4 to 5 percent, while an obese person could have as much as 30 percent or more body fat.
While some body fat is deemed to be essential, too much fat is bad for your health. The more fat you are carrying, the greater your risk of developing serious medical conditions including diabetes, heart disease, hypertension, certain cancers, gallbladder disease, arthritis, sleep apnea, depression and premature death. Losing weight, or more specifically fat, will reduce your risk of suffering from these and other associated diseases.