Commenting on Body Mass Index

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In my introduction to calorie restriction (CR), I mention body mass index:

Weight loss should be mentioned in the context of CR, even though it is not the primary goal of a CR diet. Medical experts agree that being overweight is harmful to your long term health in many different ways. Excess weight increases risk factors for conditions ranging from diabetes to cancer to Alzheimer's. It is no exaggeration to say that if you are overweight, you will have a shorter, less healthy life - many recent studies suggest that even a little excess weight is very bad for you. Bearing this in mind, it is an excellent idea to check your Body Mass Index (BMI) and consult with your physician about your weight.

Greg Ferguson e-mailed the following comments:

Use of BMI is not a good indicator of good body composition -- I put to you that the use of a fat percentage indicator is much more reliable.
For example, I am average height, in my mid-30's and am lean enough that I have a "six-pack" stomach, yet at 5'10, 190 lbs, my BMI of 27.3 would indicate that I am overweight. My fat percentage is 9%. I am most certainly not fat.

BMI is an outdated concept and following it leads to a reduction in life span. People become "skinny fat" -- they drop their overall weight, but it is the muscle and bone mass they lose to do so.

For men, aiming to keep body fat between 7 to 10% is an excellent plan. For women, aiming to keep body fat at approximately 19 to 20% is an excellent plan. Women require additional body fat for reproductive health. Maintain body fat through a combination of cardiovascular activity, smart diet choices using fresh vegetables and good protein sources and regular weight training is a much, much healthier goal and has been proven to extend life span and vitality throughout that life.

About.com has more background on body fat percentage as a measuring tool and what is currently considered average. Anyone else want to weigh in on the merits of various ways of estimating your body composition and how that relates to health and calorie restriction?