Is It Accurate?

Have a question about your low-carbohydrate lifestyle for our experts? Ask it here.
Karen Collins, MS, RD, CDN

Your question:
Is BMI still considered an accurate assessment of a healthy weight?

The expert answers:
Yes. But there are a few exceptions that may apply. Because muscle weighs more than fat, researchers have always warned that the Body Mass Index (BMI) overestimates body fatness in athletes with low body fat and a lot of muscle.

Likewise, BMI underestimates body fat in the elderly or people who have lost a lot of muscle. Body fat can be accurately assessed by underwater weighing. Trained fitness professionals using calipers or other special equipment can also closely calculate how much body fat a person has.

But in the absence of these specialized techniques, BMI has been shown to more closely represent body fatness than a simple weight measurement.

Furthermore, studies show that people whose BMI classifies them as overweight experience a greater risk of cancer, high blood pressure and high cholesterol. Because most Americans lead a lifestyle that is too sedentary, a high BMI usually comes from fat, not muscle.

Thus, a BMI reading is a good place to start when determining health risks due to excess weight. By taking a waistline measurement -- another easy test -- you can better assess health risks from body fat. For women, a waist measurement of 35 inches or more indicates high risk. For men, the significant figure is 40 inches or more.

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