I have recently received a number of emails regarding how to measure body composition, what's the most accurate method, etc. To help clear the air, I've pasted in an excerpt from my Fitness Nutrition Coach program now available! This comprehensive program, with nearly 100 pages of material, along with a textbook and audio CD, has been described as the "Cliff's Notes" version of nutrition.
It is ideal for trainers attempting to answer confusing questions from their clients, in addition to being useful for those just trying to learn the truth about nutrition to optimize their physiques and health.
Researchers have reported ranges of relative body fat for successful athletes within specific sports, but body composition itself cannot predict athletic success. However, because body composition may have a significant impact on health and physical performance, scientists have developed a variety of techniques to measure various body components.
The four major components
Total Body Fat
Total Body Fat consists of both essential fat and storage fat. Essential fat is necessary for optimal functioning whereas storage fat is simply a place (or places) for excess energy.
Fat-Free Mass consists primarily of protein and water. Skeletal muscles are the main component of fat-free mass, but organs such as the heart, kidneys, liver, etc. are also included.
Bone is crucial for body structure and some metabolic processes. This can be accounted for through various body composition assessment techniques.
Average adult body weight is roughly 60 percent water. This too is accounted for in a variety of body composition techniques.
Analyzing Body Composition
There are over a dozen different methods to analyze body composition. This piece will briefly review some of the more popular assessment tools, their strengths and limitations. The full chapter discusses several others; many are used by trainers and fitness clubs and can be one great tool to measure a client's progress.
Air Displacement Plethysmography (APD)
This is a fairly new technique to measure body composition. One of the more popular commercial products available is called the Bod Pod, which essentially looks like a large egg that a body can fit inside.
Research has suggested that this method of measuring body composition is similar to that of UWW; the beauty is that it is less cumbersome, portable, easy to operate, requires little time, and eliminates the need to go underwater (which may scare individuals away from UWW).
Underwater weighing (UWW)
Considered by most to be the foremost method of body composition assessment, UWW is a laboratory technique involving some rather spendy equipment (~ $70,000) and 2 to 3 technicians and a patient subject willing to sit through the 25 minute process. The underwater process allows for air volume to be subtracted from weight totals, thus giving a more accurate reading.
It is an extremely expensive machine, though, so it is not likely a trainer would purchase one on their own; there is a potential for a large fitness club to have a Bod Pod or access to a Bod Pod, maybe through a local University.
Bioelectrical Impedance Analysis (BIA)
This technique to measure body composition uses the concept that lean tissue and water conduct electricity better than fat. In this method, a low-level electrical signal (that the person does not feel) is passed through the body. Based on the resistance to the signal, total body water is calculated and the value can be used to estimate percent body fat.
The signal can be conducted by standing on a scale where the signal is passed from one foot to the other and extrapolated to the upper body. Another method is to pass the signal from electrodes placed at the hand and foot. The reading is then extrapolated from one side of the body to the other, and tends to be a more accurate measure of total body water than the foot to foot placement.
BIA is fast and easy to administer and fairly inexpensive (ranging from $100 for scale type models to $3000 for clinical electrode models). Several instructions need to be followed in order to ensure greater accuracy. These include maintaining normal hydration status, not participating in vigorous exercise within 12-24 hours, and refraining from eating within 4 hours of measure as these may affect total body water, and hence, the body composition reading.
The error associated with BIA ranges from 3 to 5%, and is dependent on the above mentioned factors for greater accuracy.
Dual Energy X-ray Absorptiometry (DEXA)
DEXA is becoming the new "gold standard" because of its accuracy, precision, and reliability. The DEXA uses a whole body scanner that has two low dose x- rays at different sources that read bone and soft tissue mass simultaneously.
This technique is based on the assumption that bone mineral content is directly proportional to the amount of photon energy absorbed by the bone being studied. The scanner passes across a person's reclining body and takes between 10-20 minutes.
It is safe, noninvasive, and less demanding on the individual as the person simply has to lie still throughout the procedure. DEXA has the advantage over underwater weighing (described below) of providing a measure of bone mineral content in addition to fat mass and fat free mass and is also unaffected by fluctuations in hydration status unlike UWW and bioelectrical impedance.
Furthermore, it shows exactly where the fat is distributed throughout the body. However, the major downside is that this piece of equipment is rather expensive, so they are most likely only going to be found in Universities, hospital, or other similar settings.
Body Composition Summary
For health purposes, it is recommended that the minimum level of fat for males is 3% and 12 to 15% for females. The current average percentages of body fat for U.S males and females are approximately 15 to 18% and 22 to 25%, respectively.
While there are no guidelines that correlate to peak performance in athletes, it is understood that some athletes (wrestlers, gymnasts, etc) will most likely perform better with lower body-fat levels. Others, like football lineman or shot-putters, for example, will more than likely have higher body fat values.
Athletic males and females typically range from 6 to 10% body fat and 10 to 15%, respectively. A "good range" is considered 11 to 14% for males and 16 to 23% for females, and an overweight individual is typically 21 to 24% for males and 31 to 36% for females.
These are all approximate values, but appear to correlate well to the general population.