The amount of fat in the body is an indicator for risk of disease and being able to measure the percentage of fat in a body allows one to see if their body composition is as it should be, meaning if they are healthy or not. If they are not physically fit, then they can start doing something about it before problems such as hypertension, diabetes or high cholesterol arise. There are several ways of measuring the amount of fat in your body, namely there is the BMI index, girth measurements and the skinfold measurement test. Each method comes with its own set of advantages, and disadvantages
Until recently it was believed that the only function of fat tissue was to provide insulation for your body. But research uncovered that it actually produces a hormone called leptin, and this hormone gives the feeling of being full, satiety. Needless to say the pharmaceutical industry jumped on the idea of promoting leptin as the miracle to control appetite, and eventually weight. When there is sufficient fat stored in your body, 3 to 5% in men and 8 to 12% in women, the fat cells release the hormone leptin into the bloodstream. Since leptin is released by the adipose tissue, it proceeds to do so only when there is sufficient amount of it stored in the body. The level of leptin rises in the blood when a person gains weight and decreases when a person loses weight. Theory is that when there is a greater concentration of leptin in the blood, the body will stop storing any more fat. When leptin is released in the blood, it is a signal to the brain that there should be no more food intake. At the same time, leptin signals the brain to increase the amount of energy being used by the body. Leptin acts on a part of the brain called the hypothalamus where it inhibits appetite. The lack of leptin in a body due to genetic disorder leads to rampant food intake which brings on obesity.1 Dr. Scott Isaacs, author of “The Leptin Boost Diet” and “Hormonal Balance,” states, there is no sure shot method of determining the level of leptin in the blood, but other methods may be used to conclude leptin resistance levels. It has been determined that the level of leptin in overweight people is higher than people of normal weight.2
The BMI is a number that compares the weight of a person to the height. It was developed in the mid eighteen hundreds by Adolphe Quetelet, but gained popularity in 1972 when Ancel Kely found that it was the best substitute for body fat percentage in ratios of height and weight. It is a very reliable method of identifying individuals with weight problems, thereby allowing the prevention of diseases before they start. Although it is not a direct measure of how much fat there is, it is a good indicator of the percentage of body fat. It will however, not work for athletes as it does not take into account the muscular development of athletes.3
The formula for calculating the BMI for adults is to take the weight measured in kilograms and divide it by height in meters, squared. A BMI of less than 18.5 is considered underweight, 18.5 to 24.9 is normal and 30 and above is obese. Best part is that it is a very easy and inexpensive method; all that is needed is a tape measure, weighing scale and a calculator.
Girth measurements are sometimes used to measure the fat in a body by taking circumference measurements at standard sites on a body. The sites to be measured are neck, shoulder, bicep, chest, waist, hips, calf and thigh. The accuracy of these measurements is only as good as the person taking the measurements, correct marking of where the measurement should be taken on the body and the quality of the tape used (plastic tape measures tend to stretch with use giving rise to inaccurate measurements). The good news is that this is also a relatively cheap method, the only thing needed for conducting the test is a tape measure and a marker, and the test can be repeated numerous times, thereby eliminating the chances of error. However, it is not reliable for people who are very over weight or under weight and even you do not belong to this category these measurements are still off by four percent!
The 7 site skinfold test estimates the body fat by making use of skin fold thickness measurements. To carry out the test a caliper is used to take measurements from three to nine different sites on the body. The tester will pinch the chosen sites to raise two layers of skin in such a way that only the top skin and adipose tissue are raised and not the muscle. Three readings at each site should be taken, and the two closest should be kept for calculations. The sites used most frequently are triceps, chest, midaxillary, subscapular, supraillac, abdominal, and thigh. All measurements should be taken while standing up and same side (preferably right) should be used for all measurements. Next a calculation is done which is based on the sum of all these measurements. One disadvantage is that different prediction equations are used for different age groups and ethnic backgrounds. There are over 3,500 valid equations
Skinfold test is fairly easy to do and not expensive. The accuracy of the tests however, depends on how experienced the technician is and the quality of the calipers. Another factor is that the calipers need to calibrated, which leaves margin for error. Needless to say, a professional using the more expensive models will get more accurate results than an amateur using the cheap home variety. The more obese a person the harder it is to pinch, so greater the chances or error.
Although the skinfold test does not give a precise measure of the fat in the body, it is a good indicator of the change in the body composition over a span of time. The other problem with the test is that it only measures the fat that is found under the skin, but does not take into account the fat found in the abdominal cavity. So two individuals can have the exact skinfold measurements, but if their fat deposits are concentrated in different parts of their bodies, their fat percentages according to this method will vary greatly.
Although all the methods of measuring body fat discussed are good when used as general guides to approximately determine if your body fat is in a safe zone, or the danger area. None of these is precise. The BMI and girth measurements do not even measure the amount of fat found in a body directly, and while the BMI is fairly accurate for most adults it is not suitable for the elderly, who do not have much muscle mass. The girth method also cannot accurately forecast the percentage of body fat, but can only point towards the changes in composition of the body over a period of time. While the skin fold method does actually measure the amount of fat in the body it too has its shortcomings. Generally speaking, older people have less body density for the exact same skinfold measurements and this indicates a higher body fat percent. On the other hand, older people who are athletic may not fit this scenario, and cause the formulas to misjudge their density.
None of these measurements can be taken at face value. It is however possible to eliminate errors by repeating the tests frequently, getting a professional to do, and only to use the results of these tests as a guide.
1. Katie Clark, MPH, RD (http://www.thedietchannel.com/node/1744)
2. Considine RV, Sinha MK, Heiman ML, Kriauciunas A, Stephens TW, Nyce MR, Ohannesian JP, Marco CC, McKee LJ, Bauer TL, et al.: Serum immunoreactive-leptin concentrations in normal-weight and obese humans. N Engl J Med 1996;334:292-295.