Thursday, 16 February 2012

Understanding Your Body Composition

When discussing ones body weight, people always ask what their body mass index (BMI) is, as if it’s the most important thing to consider with regards to their health. Many of you will know that BMI is a calculation that is used to determine the ideal body weight according to ones height. The following formula can be used to calculate BMI:

BMI = Weight (kg) / [Height (m)]2

Obesity puts one at an increased risk for cardiovascular disease. Below is a table which gives normative values for BMI, as well as the associated risk of disease for a specific BMI range.

Classification
BMI (kg/m2 )
Risk of other obesity related medical complications
Underweight
<18.5
Low (but has risk of different set of other clinical problems)
Normal range
18.5-24.9
Average
Overweight
25.0-29.9
Mildly increased
Obese
>30.0
 
Class I
30.0-34.9
Moderate
Class II
35.0-39.9
Severe
Class III
>40.0
Very severe
Adapted from ACSM’s Guidelines for Exercise Testing and Prescription (7th ed.).

While BMI is a useful tool in determining appropriate body weight and associated disease risk, it has its limitations which it is important to be aware of when assessing your body weight for health.

BMI does not consider the composition of the body, that is, what portion is muscle and what is fat, a very important distinction to make. A higher fat percentage puts one at an increased risk for cardiovascular disease. However, it is possible that a person with a BMI that classifies one as ‘obese’, when in fact the person is a body builder and has a very high muscle mass. The image below illustrates this. On the other hand, one may be anorexic and have a high fat percentage.


The area of the body where the weight is carried must also be considered. Men tend to carry most of their weight in the waist area, whereas women tend to carry it in their hips. Carrying it in the waist area puts one at an increased risk for cardiovascular disease, as it is closer to the heart and other vital organs. Thus, it is important to monitor ones waist circumference as well when considering health risks. As a guideline, men should have a waist circumference below 102 centimetres and women below 88 centimetres.

So, don’t panic if you find out that a reading, such as your BMI, is slightly high. There are numerous other calculations and factors to consider when looking at your weight and your general well-being.


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