Total human body mass is composed of fat tissue and lean body mass. Lean body mass includes components such as muscles, organs, bones and water--essentially everything that isn't fat tissue. The proportions of the components that make up body mass vary depending on age, gender and activity level. Body composition recommendations differ by gender. There are several methods available to help estimate body mass composition.
Body Mass Index (BMI)
Body mass index, or BMI, is used to provide an assessment of body mass composition. BMI is a number calculated by using a person’s height and current body weight, and is determined using the same formula for adult men and women of all ages.
BMI can be calculated by using the following formula: BMI = weight in kilograms divided by the square of the height in meters.
For customary U.S. units of measurement, BMI can be determined using this formula: BMI = weight in pounds divided by the square of the height in inches, multiplied by 703.
Interpreting BMI
BMI is considered a reliable estimate of body fatness, according to the Centers for Disease Control and Prevention, or CDC. BMI is commonly used to help determine if body weight is in a healthy range. According to the CDC, individuals with BMIs less than 18.5 are considered to be in the underweight range; those with BMIs 18.5 to 24.9 in the normal, or healthy, range; those with BMIs 25 to 29.9 overweight, and those at 30 and above obese.
Other Assessment Tools
There are other methods of estimating body mass composition that provide more direct measures than BMI. However, they require more specialized equipment than BMI calculation and may require highly trained personnel. The aim of each assessment method is primarily to estimate the fat component of body mass.
These body composition tests include skin fold measurements, waist-to-hip ratio, bioelectrical impedance analysis or BIA, and underwater weighing, according to AIDS InfoNet. No method provides 100 percent accuracy; of these methods, skin fold measurements are the most commonly used due to low cost and convenience.
Body Composition
Body mass composition recommendations are different for men and women. Medline Plus recommends a healthy body composition of 20 to 21 percent body fat for women and 13 to 17 percent fat for men. Medline Plus also states that individuals are considered obese if they are women with more than 30 percent body fat or men with 25 percent or above body fat.
Effects of Exercise
Participating in daily physical activity can drastically alter body composition by increasing lean body mass and decreasing body fat. Exercise is particularly effective when combined with a healthy diet. Exercise can also enhance body shape by increasing muscle definition.
Older Age
Lean body mass decreases with increased age, according to Medline Plus. Older age typically causes a decrease in muscle mass and bone density, and an increase in fat tissue, especially in the abdomen. Exercising regularly, avoiding tobacco smoke, limiting alcohol and following a healthy diet can help counter the effects from aging on body mass.
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