Since the health risks of being overweight are mostly related to excess fat, many people think they should check how much body fat they have. Technology to estimate body fat levels has now become readily available. With the numbers you get, which are only estimates of your actual body fat, you can roughly chart your progress reducing excess fat.

Excess weight from body fat can damage knees and hips. It also produces hormonal and metabolic changes that increase the risk of diabetes, heart disease and several forms of cancer. Body Mass Index, known as BMI, is a way of expressing weight that can predict a person�s risk for all of these diseases. BMI is a good tool for most adults, but it can encourage people with more muscle or heavy bones to lose weight unnecessarily. It�s also inappropriate for those who are elderly or who have lost a lot of muscle.

There is general agreement that the BMI ranges for normal, underweight, overweight and obese weight categories are accurate. However, there are no corresponding universal standards for identifying healthy and unhealthy levels of body fat. One chart may list your body fat level as normal, while another may not.

Health experts emphasize that any body fat standards should allow for wide differences in inherited body types and changes that may be normal as we age. One accepted standard states that women should aim for a range of 19 to 35 percent body fat, while adult men strive for 8 to 25 percent. Athletes have slightly lower ranges, but going below 5 percent fat in men, or 16 percent fat in women, poses health risks and doesn�t increase performance.

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A special tank that weighs a person underwater or a special X-ray test known as DEXA are considered the best tools for measuring body fat. But now special scales are available that measure your weight and also estimate your percent of body fat based on Bioelectrical Impedance Analysis (BIA). These scales do not actually measure body fat. They measure how much your body resists a tiny electrical current. More body fat means more resistance. Based on the amount of resistance and other personal information, the scale calculates an estimate of your body fat percentage.

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BIA produces results close to the two traditional �gold standard� methods. However, in some studies, figures vary by two to five points. When precision is vital, BIA is not used. BIA cannot measure short-term changes in body fat due to diet or exercise, but it can record long-term fluctuations.

If you want to use a BIA body fat scale, choose your model carefully. Since the scale�s readings are based on standardized calculations, people who exercise even a few hours a week should get a model with an �athlete� mode that uses an adjusted calculation.

Carefully follow the scale�s directions, or your results can be significantly skewed. BIA measures how the tiny electrical current runs through fluid in the body, so anything that changes your fluid balance changes your results. Alcohol, caffeine, medications, hormonal changes, recent exercise or drinking, even use of the toilet, can affect the reading. Each time, test yourself at the same time of day under the same circumstances.

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Many health clubs and physical trainers offer another option for assessing body fat: special calipers designed to measure skinfold thickness in several spots. These measurements are then used to calculate an estimate of body fat. Their accuracy varies widely, however, depending on the skill of the person performing this test.

Since waistline fat poses the greatest health risk, you could also just measure your waist. A number of studies validate the greater health dangers associated with a large waist. A waist measurement over 40 inches in men, or over 35 inches in women, puts you at risk.