Fat, Body Fat Measurements
Fat is a component both of the food ingested and of the body. Fat exists in a number of structural forms. Some types of fat can be beneficial, as an energy and an insulation source, and, in the case of fats containing high levels of omega-3 fatty acids, perhaps as an aid to retard the development of cancer. Other types of fat are detrimental to health, exemplified by the artery-clogging form of cholesterol, which can promote the damage or death of heart tissue.
There are four types of fat, based on their structure: saturated fat, monosaturated fat, polyunsaturated fat, and trans fat.
In a saturated fat, all the chemical connections between the component molecules are fully occupied. This produces fat that is hard at room temperature. Saturated fats, typically of animal origin, are the least healthy. Saturated fats can contribute to the buildup of a compound called low density cholesterol, which in turn can lead to formation of solid deposits in the arteries (another form of cholesterol, high density cholesterol, is "good" in that it helps carry cholesterol out of tissues). The restricted flow of blood through these clogged arteries can cause debilitating or fatal heart malfunctions. Monosaturated fat is found in vegetable oils. In conjunction with a low-fat diet, monosaturated fat can act to reduce cholesterol levels. This fat is liquid at room temperature.
In an unsaturated fat, not all the chemical connections between the component molecules are occupied. This produces a compound that is liquid at room temperature. Polyunsaturated fats, where more than one connection is involved, are known as essential fatty acids, and are very desirable for a health diet, causing a reduction in the level of the "bad" cholesterol. Plant oils such as soybean, cottonseed, corn, sunflower and safflower contain polyunsaturated fat.
A most undesirable fat is the so-called trans fat, formed commercially by the addition of hydrogen molecules to produce an unsaturated-like fat having a palatable taste. Trans fats both raise the level of "bad" cholesterol and lower the level of "good" cholesterol. Trans fats are present in most margarines.
In proper amounts and type, body fat serves a useful and healthy function as an energy source, component of membranes that surround cells, and as a temperature insulator. The body fat content can be determined in a number of ways. The percentage of body fat can be calculated from equations based on the density of the body, involving weighing a person suspended on a trapeze in the air and then weighing the person when immersed in water. Immersion measurement has been the reference standard of body fat determination. However, it does not take into account the location of the body fat, and the equation used in the calculation was derived from studies on young Caucasians. Ethnic variations in body fat composition would not be recognized by the immersion method.
Other methods used to estimate body fat are skinfold measurement with calipers, the shift in the wavelength of near infrared light following its interaction with fat, determination of the so-called body mass index (BMI); the relationship between weight and height, and measurements of the circumference of various parts of the body.
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