The different methods of evaluating body composition range in validity, reliability, cost and accessibility. Body mass index and skinfold measurements are two of the more cost-effective methods. They both fall under the category of anthropometric measurements, but each method is distinctively different.
Body Fat Perccentage
When working with a personal trainer, he may measure your body fat percentage. This evaluation is based on the fact that the body is comprised of fat and fat-free masses. Percent body fat is the amount of fat that your body has on it. Men and women all need a minimal amount of fat on their body for it to function properly, this is called essential fat. The American Council of Exercise notes that the percentage of essential fat is between 2 and 5 percent for men, and between 10 and 13 percent for women. Keeping in mind that most of people have more than essential fat on their bodies, the body fat percentage range that is considered acceptable is 18 to 25 percent for men and 25 to 31 percent for women.
Skinfold Measurements
Skinfold measurements predict body fat percentage. A trained technician uses a high-quality caliper to pinch the areas of fat on the body and measure them. The measurements, taken in millimeters, are then placed into an equation to compute percent body fat. There are several equations, each used for different populations. Each of these equations also requires the assessment to take place at different sites on the body. Skinfold measurements are considered one of the most reliable methods of predicting body fat, when performed correctly.
BMI
Body mass index, or BMI, is a method used to evaluate weight with regards to height. How you determine is to take your weight in kilograms and divide it by your height in meters squared. This gives you a number which health professionals use to determine your disease risk. Ideally, BMI should fall between 18.5 and 24.9 to fall into a category considered a low risk for disease. Typically, a BMI higher than 25 indicates an increased risk for obesity-related diseases like cancer, cardiovascular disease and diabetes. Conversely, a BMI less than 18 is also considered unhealthy. BMI does not predict percent body fat, however, researches are working on a method to do this. Until this method is perfected, use other methods to determine percent body fat.
Benefits
Skinfold measurements are considered a reliable method for evaluating percent body fat when comparing it to the gold standard of densitometry. The body mass index is easier to administer--all it takes is a scale, tape measure and a calculator. With the obese population, BMI is a better method of assessment because the calipers used with skinfolds often cannot grasp all of the fat present.
Limitations
One drawback of skinfold assessment is that it requires a trained technician to properly evaluate. It also is a more labor intensive. The calipers usually cost about $300, which is inexpensive compared to some of the equipment that professionals use, but when comparing it to BMI it is more expensive. BMI also has its own limitations. The first being it does not distinguish between fat mass and fat-free mass. Therefore, an extremely muscular person may fall into the category of obese when she has little fat on her body. And, it doesn't give any information on how the weight is distributed, which is often key in classifying disease risk.
References
- American Council on Exercise: Percent Body Fat Calculator
- "ACSM's Guidelines for Exercise Testing and Prescription," 7th edition; Lippincott Williams & Wilkins; 2006
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