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I was reading your article about BMI and WHR today. I didn't understand what one had to do with the other. What is a good Waist to Hip Ratio and what is a bad one?
As a physician I look to have an idea of how my patient's health might be overall. I am looking for certain risk factors for disease, and the research has come to show that being overweight or obese can be an issue. In looking at my patient's weight I want to have a guide of what a healthy weight is, but we now also know that the distribution of the weight on the body is an important factor.
Body Mass Index (BMI) is an indirect measure of weight as it relates to height. It's not a perfect measurement, but for most folks it can give us an indication of whether they are overweight or obese. Because it is an inexpensive measurement, BMI is widely used in research to substitute for much more sophisticated measures of body composition, including such things as body fat percentage. Because the measures only take into account height and weight, the measure can be inaccurate for those who are very muscular (they may weigh a lot, but the weight is in healthy muscle not fat).
This is where Waist to Hip Ratio (WHR) comes in (there's a calculator and guidelines for optimal waist to hip ratio at that link). The research has shown that those with a high BMI who have their excess fat centered at the waist are at higher risk than those with the weight more evenly distributed. A ratio in women over 0.8 or 0.9 in men is considered to be too high.
Keep in mind that these are indirect measures and good doctors use them as guidelines. There are a lot of risk factors for conditions such as heart disease. This handout (PDF) discusses some of the others.
Thanks for writing,
Timothy S. Harlan, MD, FACP