Читать книгу Nutrition For Dummies - Carol Ann Rinzler - Страница 59

A tape measure or a weight chart is a low-tech tool anyone can handle. But science loves complexity, so weight experts have several complicated ways to figure out if you’re fat. Here are three of the most interesting. Warning: These are not your handy home tests — they’re performed in some doctor’s office but more likely in a research hospital or bariatric clinic.

 Bioelectric impedance: Your body is full of fluids packed with electrolytes, such as sodium and potassium, ions that conduct the electrical impulses that send messages back and forth among your cells. Muscle tissue contains more fluid than fat tissue, so a body with more muscle than fat is less resistant to an outside electrical current. To measure your body's resistance to electrical current (a phenomenon known as impedance), the technician conducting the test places electrodes at your wrists and ankles and zaps a harmless low-intensity electrical current through your body. Then she calculates how resistant your tissues were to the current. The final number indicates how much body fat you have.

 The BOD POD: This egg-shape chamber measures how much air you displace when you step in. Because muscle is denser tissue than body fat and displaces more air, the tech running the test can calculate the amount of fat in your body by looking at your weight and then at the amount of air you push aside when you enter the chamber.

 Dual-energy X-ray absorptiometry (DEXA): This test uses X-rays to measure muscle, bone, and body fat. The test — which takes about ten minutes — produces an image of the tissues that allows the tech to estimate the amount of body fat.