What Is Fat Free Body Mass?

The book "Exercise Physiology" defines fat free mass as your total body mass, but excluding the fat. Fat free mass includes everything from your skin, bones, ligaments and tendons, to your organs and water content. A high level of fat free mass generally implies a lean and healthy body frame, but there can be too much of a good thing, and too much fat free mass can be unhealthy.

Fat Free Mass Limits

Men and women require a certain amount of fat to live. This essential fat helps support the organs and provides energy for daily movement. According to "Exercise Physiology," falling below the acceptable level of essential fat can severely alter normal bodily functions.
A man's body requires at least 3 percent essential body fat to function properly. Athletes like body builders and long-distance runners often work very hard to attain a body fat percentage close to the limit of essential fat in order to excel within their sport.
A woman's lower limit for fat free mass is roughly 4 to 7 percent of her body mass, but a woman also has sex-specific fat requirements in the breasts, genitals and other areas, requiring that a woman maintain roughly 12 percent body fat for essential function.

Assessing Body Composition

Determining body composition provides an estimate of your fat free body mass. All body composition tests are done indirectly because direct testing requires physically removing the body fat and weighing it, something that's impossible in living people. Indirect assessments are often good predictors of fat free mass, but are never 100 percent accurate.
Common indirect body composition tests include girth measurements using measuring tape to estimate body fat percentage; hydrostatic weighing, a testing form that uses underwater weight to estimate body fat; skinfold testing, which uses calipers to pinch body fat on different locations of the body to estimate total body fat; bioelectrical impedance analysis, or BIA, which uses a low-frequency electrical current passing through the body to assess body composition; and dual-energy X-ray absorptiometry, or DXA, that uses X-ray technology to analyze fat percentage.
The simpler tests, like girth measurements, skinfold testing and BIA are often provided for a small fee at gyms, while the more technical tests like hydrostatic weighing and DXA are more commonly held at universities and hospitals due to the expense involved.

Too Much Fat Free Mass

A person with a very high fat free mass percentage has a very low body fat percentage. Very active women, or those struggling with eating disorders, may start creeping dangerously close to a body fat percentage between 10 to 12 percent. When a woman's fat levels drops that low, her sex-related functions, particularly her period, may become irregular or stop completely. While some women see this as a good thing, the loss of a regular period can lead to hormone imbalances that can cause bone loss and osteoporosis. The linkage between low body fat, loss of a regular period and bone loss is referred to as the Female Athlete Triad. While it's unknown how prevalent this disorder is, according to The American Academy of Family Physicians, athletes like gymnasts, dancers, long-distance runners and ice skaters are particularly prone to engaging in behaviors that lead to this disorder.

Too Little Fat Free Mass

Having too little fat free mass and a lot of body fat puts people at risk of becoming obese. The American Council on Exercise indicates that women with a fat percentage of 32 percent or more, and men with a fat percentage over 25 percent, are considered obese. Obesity comes with a myriad of health risks, including heart disease, cancer, diabetes, arthritis and skeletal abnormalities.

Considerations

A healthy fat free mass ranges between 69 to 88 percent for women, and 76 to 94 percent for men. Saying this another way, a healthy body fat percentage ranges from 12 to 31 percent for women and 6 to 24 percent for men. Healthy eating practices and regular exercise can help contribute to attaining and maintaining a healthy body fat percentage. The American College of Sports Medicine suggests at least 30 minutes of moderate-intensity exercise five days a week and strength training exercise at least twice a week.