Friday, 8 May 2009

Is Your BMI Way Too High?

I got an email this week by a distressed male who had just discovered he had a BMI of 29. "what does this mean? am I obese?" . I understood his concern. I have a BMI of 25. Technically, I am overweight. I'm sure there are a lot of people who receive information and stats, but only part of the picture. So I thought I'd put things into perspective.

What is BMI?

BMI stands for Body Mass Index. BMI is one method used to assess you weight relative to your height. Its based on the idea that there is an ideal weight in relation to height and any deviation from that can highlight potential health problems.

How to calculate your BMI

Weight (in Kilograms) / Height Squared (Height in cm x Height in cm)

So I'll use myself as an example;

86kg (on a good day) / 1.85cm x 1.85cm (3.4cm)
= 86 / 3.4 = a BMI of 25.2

This would place me at the low end of the "Overweight" category. The major problem with BMI is that it does not differentiate lean muscle mass from fat mass, or even fat distribution.

BMI should be taken into account with your body fat percentage, as well as your hip to waist ratio. This will give you a more accurate picture of your body composition. Fat distribution is equally important. A problem area for men is abdominal obesity. This has strong links to Cardiovascular disease, type 2 diabetes, certain types of cancer and high cholesterol. So taking BMI in conjunction with your waist to hip ratio would be beneficial, so even if you had a BMI of below 25 but your waist to hip ratio (waist measurement / hip measurement) was close to 1 or above, then you would definitely want to look readdress your nutrition, physical activity, and your lifestyle.

Taking your body fat percentage is probably the easiest and most effective method of identifying your body composition. Make sure you take about 3 readings from correctly calibrated machines in one sitting, as there is a standard estimate of error of a few percent. A high body fat percentage will instantly tell you whether your health is at risk, but equally a very low reading of body fat percentage can be unhealthy.

There is an essential level of body fat required for your body to function and create the appropriate hormones. Essential body fat for female reproduction is generally 8 - 12% (ACSM Physical Fitness Assesment Manual: Lipcott Williams & Wilkins: 2005). Women with a body fat percentage lower that this may experience disruptions ovulating. There are issues for men as well, below are some links that will help to clarify body composition.

They key thing is to look at the whole picture. You know you better than anyone else. Are you physically active and getting exercise in? Do you drink too much or only the odd tasty beverage? Hows your nutrition? Taking your body composition is only a tool for you to let you know where you are in terms of health, and your lifestyle. The important thing is what are you going to do about it? and therein lies the question!

To find out more about BMI and BMI Charts Click here
To find out more about Body Fat Percentage and Charts click here
For more on Body composition click here

I found these useful pages on wikipedia, but remember, always check the source!

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