Skinfold measurements

One of the main determinants of the number of subjects required to reach the desired statistical power is the precision of the measurement tool utilized. More precise measurements will reduce the number of subjects required. As an example, if a study is being conducted to assess the influence of a dietary supplement on body fat, several measurement tools could be used to assess this outcome. These tools range from low levels of cost and precision (e.g. skinfold measurements) to moderate levels (e.g. bioelectrical impedance) to high levels of cost and precision (dual x-ray absorptiometry - DXA). A study that uses skinfold measurements to measure the outcome will require many more subjects than one which employs DXA. Therefore, it is often less expensive in total to utilize a more expensive measurement tool, because the more precise tool will allow the study to have sufficient power with a smaller number of subjects. 

The patients were weighed three times a week, and skinfold measurements were taken periodically of the abdomen, triceps, subscapular areas, using skinfold calipers according to the procedure outlined by the manufacturer (Cambridge Scientific Industries, Inc., Cambridge, Maryland). 

Skinfotd measurements. Skinfold thickness is measured by pinching the skin and using calipers to measure the layers of skin and subcutaneous fat that are located to the side of the pinch. The skinfold measurement is a fairly direct measure of the subcutaneous fat at the tocahon of the pinch, but the usual goal of the method is to gain an indication of total body fat-... 

Ultrasound. The technique of ultrasound is familiar to pregnant w omen who have had their fetus examined, i e, to determine the growth and position of the fetus. In nutritional studies, ultrasound is used to determine the thickness of subcutaneous fat. The technique gives results that are similar, but not quite idenhcal, to those acquired from skinfold measurements. Skinfold measurements tend to be difficult to acquire in very obese subjects, and here ultrasound may be the preferred technique,... 

Pregnant women have provided a striking illustration of subcutaneous fat (Taggart ei ai, 1967). The pinch test or, more accurately the skinfold lest, was performed on 84 women during the course of their pregnancy Data were taken at the indicated times, i.e, from week 10 of the pregnancy until 8 weeks after birth (Figure 7.1). Skinfold measurements were acquired at various sites of the body. 

A number of different sites have been used to apply the pinch. The most commonly used site is over the triceps muscle of the arm. Hence, the site is called the "triceps skinfold" site. The measurement is taken halfway between two bones, the scapula and ulna. More specifically, the measurement is taken halfway between the acromion process of the scapula and the otecranon process of the ulna (Figure 7.9). A picture of a dietician taking a triceps skinfold measurement is shown in Figure 7,9. 

Measurement of Body Fat by Skinfold Measurements Measurement of Body Fat by Densitometry Assessment of Body Fat by Computed Tomography Signaling Pathways for Regulating Adipocyte Formation Genetic Factors in Obesity... 

FIGURE 7.3. Adipose tissue thickness in people in the general population (solid bars) and in obese persons (dashed bars). Adipose tissue thickness was measured by ultrasound measurements (not by the usual technique of skinfold measurements) at the gluteal site (G), femoral site (F), hypogastric site (H), and epigastric site (E). The epigastric site that was used was one-third the distance down from the tip of the sternum to the umbilicus. This site was somewhat thicker in men than in women. The femoral site was one-third the distance down from the anterior superior Uiac spine (wide part of the pelvis) to the patella (knee). This site was much thicker in women than in men. Biopsies were also taken at the indicated sites and examined imder the microscope to acquire fat cell size. (Redrawn with permission from Krotkiewski et ah, 1983.)... 

Skinfold measurements reflect the thickness of layers of fat at specific points of the body. In contrast, the technique of densitometry is sensitive to the proportion of fat in the entire body. Density, whether measured by chemists, physicists, or dieticians always means mass/volume (grams/ml). The density of a human being is often measured by using rmderwater weighing. This technique requires a tub of water, a scale for measuring the subject s weight, and a special chair that is attached to the scale. The subject needs to have defecated and urinated shortly... 

Body composition is a more sensitive indicator of infant nutritional status than measures of size. Depending on the method used, measurements can provide the mass of lean tissue, fat tissue, total body water, and bone. Methods vary greatly in terms of invasiveness, feasibility, cost, technology, need for trained personnel, accuracy, reliability, and precision. The most feasible methods for assessing infant body composition include anthropometry (e.g., skinfold measurements), dual X-ray absorptiometry (DEXA), and isotope dilution. A recent review concluded that for intergroup comparisons, skinfold thicknesses were useful, but for individual infant assessments, DEXA was recommended (Koo, 2000). In the absence of reference data based on a large sample of infants, the interpretation of body... 

Pinch Jests for Hidden fat. Skinfold measurements are more precise versions of the long used pinch tests for obesity. In a pinch test, one selects an area of the body where fat is likely to be deposited and grasps a double fold of skin between his thumb and forefinger. Excessive fat is present when the thickness of the double fat is an inch (2.5 cm) or more. Special calipers are available for accurately measuring skinfold thicknesses. The use of these calipers is shown in Fig. 0-6. 

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