Body fat analyzers: How accurate are they?

I am 46 years old and exercise regularly. My BMI is 24.1, which is in the normal range. A hand-held device used at my health club to measure body fat says my body fat percentage is 40 percent, which is extremely high. Which number should I believe?

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Mayo Clinic physical medicine and rehabilitation specialist Edward Laskowski, M.D., and colleagues answer select questions from readers.

Answer

Body mass index (BMI) is based on a formula that uses both weight and height to estimate body fat and the associated health risks. Your BMI is a general measurement that can help guide your diet and exercise program. However, BMI doesn't provide a specific body fat percentage. And the body fat percentage you get from hand-held body fat analyzers can vary depending on many factors, including how hydrated you are when the measurement is taken. In fact, it's difficult to get an accurate body fat measurement from most commercially available body fat analyzers. If you're concerned about your body fat percentage, skip the body fat analyzers and ask your doctor about more accurate measurement techniques.