18.3 Body Composition

Body Composition Defined

Body composition is the relative proportion of fat to lean mass in the body. Lean body mass consists of water, organs, teeth, bone, connective tissue, and muscle. Fat mass within the body can be divided into essential and non-essential fats. Essential fat is necessary for normal body function. Your body needs fat to function. The brain, nerves, heart, lungs, liver, and mammary glands all require some fat to work properly. The amount of essential fat is higher in females—10-13%—compared to males—3-5%—due to fat deposits in the breasts, uterus, and other sites specific to females and reproduction (American Council on Exercise, n.d.). Non-essential fat is excess fat that is stored just below the skin and around the organs. The amount of non-essential fat in individuals depends on genetics, metabolism, sex, age, diet, and activity level, to name a few.

Methods for Measuring Body Composition

A number of methods are used for measuring body composition, including skinfold tests, bioelectrical impedance, underwater weighing, Air Displacement Plethysmograph, like the BOD POD, or laboratory-based dual energy X-ray absorptiometry, mostly in laboratory settings. Individuals interested in having their body composition measured can arrange it with a fitness center in their community, a local clinic, or possibly a campus wellness center.

Cardiorespiratory endurance and muscular strength and endurance impact body composition. Engaging in regular exercise helps increase the proportion of lean body mass—specifically muscle—relative to fat mass, which is an indicator of improved fitness.

Body Composition is One Measure of Fitness, Not Necessarily Health

Body composition measurements are subject to variation due to a number of factors including rater error, hydration, pregnancy, calculation assumptions, the subject’s performance during evaluation, or their race, age, sex, and athleticism, among others. No universally superior method for measuring body composition exists.

Body fat is the most variable component of body mass; therefore, recommendations around body composition are usually framed around body fat percentage. Due to ethnic and genetic variations and natural changes in body composition throughout the aging process, body composition recommendations you may come across could be based on specific populations and, therefore, may not represent the best recommendations for you, as an individual (Lee & Gallagher, 2008).

Body composition, while one component of fitness, is not, on its own, a good indicator of overall health and wellbeing. Numerous other measures can indicate whether someone is in good health or their health is at risk. Some health concerns can be identified by health professionals using bodily fluids, like blood and urine, or by the appearance of certain parts of the body like the hair, skin, eyes, outer or middle ears, or fingernails. Personal hygiene and oral health can also be indicators of health. Body composition—and BMI and body weight—should be considered among these other indicators when assessing health.