What is the BMI?
Due to risks associated with excess body fat, it is important to identify when health problems are most likely to occur. One indicator is the BMI, which is a measure of body fatness based on an individual’s weight and height. It is calculated by dividing your weight (in kilograms) by your height (in metres squared). For example, if you weigh 75 kg, and your height is 1.78 m, your BMI is 23.67. A BMI of between 20 and 25 is considered healthy, while a BMI over 25 indicates you have excess body fat. The BMI is a well established measure of health and weight because it is cheap and easy to calculate, and is often used for large groups in scientific research and data analysis. But, individually it has less relevance for men, because it fails to differentiate between body fat and muscle mass. Men lose less muscle mass with age compared to women.
The research on BMI
A study reported in the online journal PLoS ONE (the Public Library of Science) found that BMI can often misclassify the health status of men. Researchers compared data from over 1393 patients at a medical clinic who had their height and weight measured, along with a scan to determine their percentage of body fat. BMI measurements categorised 26% of patients as very overweight, while body fat percentage scans showed the figure to be 64%. Overall, 39% of male and female patients were said to be of a healthy weight based on the BMI, yet body fat percentage scans classified them as very overweight. More specifically, 25% of men were misclassified as obese by BMI, possibly because men have a greater level of muscle mass compared to women. These inaccuracies led researchers to define the BMI as outdated, imprecise, and not a good indicator of heart health.
Practical tips to measure your health
Another failing of the BMI is that it fails to identify where your excess weight is located, yet this is important for men. A man who has a muscular upper body with a slim waist could have the same BMI as a man with flabby arms and a big gut. However, these two hypothetical men can have very different health profiles. Fat stored around the abdomen (where men typically store excess body fat) is thought to be associated with a higher risk of illness and disease compared to fat stored around the hips and thighs (which is more common in women). A far more reliable and accurate measure of your health and level of body fat is your abdominal girth. According to the Measure Up Program (www.measureup.gov.au) run by the federal Government, a man’s waist (at the navel) is best below 94 centimetres. A measurement above 94 centimetres is associated with an increased risk of chronic illness. There are also other measures of your health and level of body fat that may not be so scientific, but can be very important, such as:
References available upon request
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