Body Mass Index or BMI is a unit of measurement based on an individuals height and weight. It defines an individual’s anthropometric height and weight characteristics and classifies them into groups.
If your BMI falls between 18.5 and 25, then you are considered ‘normal weight’. Anything below 18.5 is considered ‘underweight’ and anything between 25 and 30, then the individual is considered ‘overweight’. A BMI over 30 is considered ‘obese’.
In the current health climate, we need accurate and practical yet affordable tools to measure both internal biomarkers such as our fat and skeletal muscle as well as the more easily measured external factors such as our height and weight. These are useful in predicting disease risk and mortality.
| BMI | Classification |
|---|---|
| Less than 18.5 | Underweight |
| 18.5–24.9 | Healthy weight range |
| 25–29.9 | Overweight |
| 30 and over | Obese |
CLINICAL LIMITATIONS OF THE BODY MASS INDEX (BMI):
When it comes to adults, BMI acts as a surrogate measure of body ‘fatness’ because it does not differentiate between excess weight and excess body fat. Furthermore, it does not distinguish between what could be excess fat, muscle or bone mass. I believe that BMI is flawed in the way that it does not take into account important factors such as age, sex, fitness, genetics, health predispositions and more. All of these variables can influence the relationship between one’s BMI and body fat percentage.
From an anatomical and metabolic perspective, BMI alone is not a thorough enough measurement to classify one as obese. Obesity refers to an excessive accumulation of body fat and BMI does not differentiate between one’s lean body mass and one’s fat body mass. Hence, BMI should serve as an initial screening for overweight and obesity, rather than be the ‘be all and end all’. It is important that factors such as dietary intake, fitness, fat distribution, genetic predisposition and more are taken into account when identifying an individual’s health classification in one of the above areas.
One example of how BMI results could be skewed is the fact that on average, females have greater amounts of total body fat than males with an equivalent BMI. In a similar way, muscular individuals or those with an athletic build, may have a higher BMI because of increased muscle mass and we know that muscle weighs more than fat.
The BMI traditionally is meant for adults and does not work in the same way in children. Whilst, it is generally calculated in the same way, the results are interpreted differently. For children and young adults between the ages of 2-20 years old, BMI is interpreted relative to the child’s age and gender, due to the ever changing growth pattern of individuals between these ages.
IS IT USEFUL AT ALL?:
Whilst for an individual this may not be a perfect measure, when it comes to population-based health and studies, the BMI has been useful as a determination of public health policies. It has also been widely used to identify risk factors associated with illness and disease. In general, I would conclude that BMI is merely a guideline and should be used in this way.