The Significance of Body Composition
I have a client who is obsessed with what he weighs, so much so that his mood du jour is determined by whether the number on his scale goes up or down. This is no way to live, nor is it an accurate report of the health of your body, i.e., how much of your body is fat vs. how much of your body is muscle mass.
Excess body fat is undesirable for more reasons than simple aesthetics. Fat is a storage site for carcinogens, and the more fat you carry above a healthy range, the more you risk hormonal imbalances which set you up for many diseases including diabetes, metabolic syndrome, heart disease, or cancer of the breast, cervix, colon, esophagus, ovaries, and prostate, to name a few.
A recent study by the American Cancer Society found that approximately 90,000 cancer deaths every year are due to excess body fat. I advise my clients to worry less about what they weigh and concern themselves more with what comprises their weight. In other words, focus on body composition, or the percentage of fat relative to the percentage of muscle on your frame.
No method of measuring body fat is 100% accurate, so always take into account the reported margin of error for that method.
The caliper method uses skin-fold measurements. It measures the fat situated immediately under the skin, above the muscle. Fat is measured at predetermined sites around the body (formulas usually have five or six measurement sites.) Most gyms can easily provide skin-fold measurement testing. Experts give this test a margin of error of 4%, meaning your actual body fat percentage could be four points higher or lower than the test indicates.
For young adults, about half their total body fat is deposited under the skin, while the remaining fat is internal (wrapped around organs.) As we age, a greater portion of body fat is situated internally.
Bioelectrical impedance analysis (BIA) measures the resistance of body tissues to the flow of a small electrical signal. A current flows more easily through the parts of the body that are composed mostly of water (blood, urine and muscle) than it does through bone, fat or air. Bioelectrical impedance measures the strength and speed of the electrical signal sent through the body (this is called an impedance measurement). It then uses this measurement and information such as height, weight and gender to predict how much body fat a person has.
Bioelectrical impedance can have a high margin of error, especially if you’re extremely fat or extremely lean. In one study, world-class female distance runners averaged 20 percent body fat, when more reliable methods (such as the caliper test) showed that they were closer to 10 percent. Dehydration also can skew the results; the signal slows down, and you appear to have more fat than you really do.
When measuring body fat using BIA, you must be adequately hydrated. This is because this method assumes that the body is within normal ranges for its water content.
Depending on whether the many testing criteria for BIA are observed, there can be a 4-20% margin of error.
The gold standard, hydrostatic weighing (underwater weighing), is the most accurate, albeit the least convenient. I tried this method in graduate school years ago in a physiology lab.
Underwater weighing is based upon Archimedes Principle, which states that the buoyant force on a submerged object is equal to the weight of the fluid that is displaced by the object. This principle can be used to determine a person’s percentage of body fat because the density of both fat mass and fat-free mass are constant. Lean tissue, such as bone and muscle, are more dense than water, and fat tissue is less dense than water. In other words, muscle sinks and fat floats, so a person with more body fat will weigh less underwater and be more buoyant. Someone with more muscle will weigh more underwater.
According to the American College of Sports Medicine, hydrostatic weighing has only about a 2-3% margin of error. This is much lower than the error rates for any of the other ways of measuring body fat.
Here are some general guidelines regarding what is considered healthy body fat levels for men and women:
Females: Up to 35 yrs=17-22%; 35 to 55 yrs=18-23%; 55 yrs and up=19-25%
Males: Up to 35 yrs=9-14%; 35 to 55 yrs=10-16%; 55 yrs and up=12-18%
Being at the lower end of the range is healthier than the higher end. Having a body fat percentage below the normal range is healthy to a point. A certain amount of body fat is required to be healthy and sustain normal physiologic function. This is called “essential body fat.”
For women, essential body fat is 8-10%. For men, essential body fat is 3-4%. Going below these amounts can put you at risk for health problems, including the cessation of a menstrual period for women.
Stay tuned for a blog about Waist to Hip Ratio, my personal favorite for keeping your health in check!
Live with Simplicity,
Tara Marie
