Is BMI still a reliable indicator of healthy weight?
Body mass index (BMI) was developed in the 1840s and has since been widely used by health professionals to give people an indication of their health. It is determined by the relationship between your height and weight and divides people into four categories:
1) Underweight – a score of less than 18.5
2) Normal weight – a score between 18.5 and 24.9
3) Overweight – a score between 25 and 25.9
4) Obese – a score of 30 or greater
Typically, the higher your BMI the more overweight you are. However, is this “one size fits all” the ultimate approach in giving us an accurate indication of our health? I’m afraid it is not. If you look closely, this calculation is based only on two variable factors; weight and height. The formula itself automatically assumes that the best method to figure out how much fat you carry is to divide your weight by the square of your height. It does not take into consideration other factors such as muscle, fat and bone proportion of an individual. Although it may be a suitable indication for people with an average proportion, it can create skewed results when applied to people outside the normal body range. For instance, a person with a higher fat content and lower muscle tone is more likely to have a lower BMI compared to someone with a significant muscle tone and low body fat. Also, BMI cannot distinguish between muscle and fat, where the later is more heavier and hence can tip more toned individuals into the overweight category.
According to the research by the University of Pennsylvania, BMI doesn’t not take into consider the different types of fat and the areas where the fat holds, each of which can have a different effect to individual’s health. For instance, belly fat, also known as the visceral fat develops deep within muscles and organs which can have a greater risk of developing health problems than other types of fat. In other words, an individual deemed healthy by BMI may have stored a high level of visceral fat which posing them at high risk of health problems.
So are there more reliable ways that we can use to give us a greater understanding of our body fat level? The answer is yes, but comes at a cost. CT scan and MRI scan can provide a clearer outlook by separating out fat from muscle. Dual-energy-X-ray-absorptiometry (DEXA) scan can distinguish fat from bone and muscle mass.
A more practical way, that can give us a deeper insight into our body composition would be:
1) Waist circumference ratio
This is an old fashioned way to see how much body fat is stored in our mid-section. Knowing your waist circumference can determine if you are at risk of heart problems. According to the Australian Heart Foundation, an adult male with a waist circumference of over 94cm and female of over 80cm regardless of height are at increasing risk of heart disease and stroke.
2) Waist to Hip Ratio
This is also a good way to indicate how much excess weight you are carrying. Simply using a tape measure and measure your waist line and your hips. Then divide the circumference of your waist line by the circumference of your hip. World Health Organisation suggests that individuals with a ratio of above 0.9 for male and 0.85 for female are classified as obese.
3) Body fat measuring using Callipers
This is a simple method to calculate out how much body fat you are carrying. Skin and fat measurements are taken from 4 areas (biceps, triceps, waist and shoulder blades) and then added up together to give a single figure (in millimeters). The figure is then matched against a chart that takes into consideration of your sex and age to determine your body fat percentage.
Although, these method can give us a rough estimation of our health. The evidence supporting those measurements and their ability to predict health problems is not definitive enough yet.
So until a more reliable way of measuring body fat becomes available, BMI is still the best option. However, I personally believe we should not just rely on one method but a combination of the above methods to give a meaningful, if not yet precise picture of our body composition.