| BMI | Classification |
|---|---|
| Below 18.5 | Underweight |
| 18.5 - 24.9 | Normal Weight |
| 25 - 29.9 | Overweight |
| 30 - 34.9 | Obese Class I |
| 35 - 39.9 | Obese Class II |
| Above 40 | Obese Class III |
Body Mass Index (BMI) is defined as weight (kg) divided by the square of body height (m) and is expressed as kg/m2. Calculating BMI is a cost-effective way to screen and categorize individuals to determine risks of developing certain diseases such as osteoporosis, hypertension, cardiovascular disease and Type 2 diabetes. Although vastly used in medicine, BMI is believed to be too simple to predict such risks since it does not take into consideration factors such as muscle mass and physical activity level. For this reason, BMI should only be used as a screening tool. We recommend utilizing BMI in combination with other assessments such as Waist to Hip Ratio as a better alternative to predict health risk factors.
We will demonstrate how the calculator works with a simple example:
A male who weights 80kg and is 1.68m tall would like to know his BMI. Let's do the math!
BMI = weight(kg) / height(m)2 = 80 kg / (1.68m)2 = 28.34 kg/m2
According to the classification table, our subject would be classified as being overweight. But remember! BMI should only be used as a screening tool.
Underweight – If you find yourself in this category, it could be a sign that you are not getting enough healthy foods with the proper amount of key nutrients to maintain normal bodily functions. Having a malnourished body could lead to excess fatigue, increased difficulty fighting off illnesses and even osteoporosis.
Normal Weight – If you are part of this category you are considered healthy and at a low risk of developing some of the diseases listed. Keep up the good work!
Overweight – Being in this category usually indicates a moderate risk of developing heart disease, hypertension, stroke, and Type 2 diabetes. A better balance between calories consumed and calories burned is key to improve your status.
Obese – Being obese indicates a high risk of developing heart disease, hypertension, stroke, and Type 2 diabetes. On a positive note, obesity is highly preventable and can be managed through lifestyle changes. Some of these changes may include a decrease in sugar intake, increase in consumption of fruits, vegetables and whole grains, and increase in levels of physical activity.
* The classification table above should not be used for children and teenagers. Additional information on how BMI is utilized for that age range can be found at the Centers for Disease Control and Prevention (CDC) website.
As previously stated, BMI has its own limitations since it only takes into consideration an individual's height and weight to determine health risks. Because of this, other methods have been proven to be more effective at measuring body composition and determining risk factors, however, these require professionals with a high degree of expertise and are not as cost-effective. Some of these methods will be discussed in the following section.
In this section we will discuss alternative methods to BMI that are more utilized in a clinical setting, usually requiring a qualified professional. These methods require specific tools that are accessible to the general public and could be found for purchasing online or specialized stores. Other techniques such as Dual-Energy X-ray Absorptiometry (DXA), Hydrostatic Weighing, and Air Displacement Plethysmography (Bod Pod) are considerably more expensive and will not be discussed in this section.
This is the most common method to determine a person's body fat percentage. Most healthcare professionals will only require a caliper to obtain the measurements while others may utilize a tape measure and a pen for accuracy purposes. There are several types of calipers in the market and most of them are fairly inexpensive.
With this method, 3 to 9 anatomical sites are used to determine body fat percentage. Some of these sites may vary depending on the person's gender and the equation utilized. A detailed video explanation on how to acquire the measurements can be found here.
Once all the measurements are obtained, your health care professional will enter it all into an equation to calculate your body density. Only after that, he/she will be able to accurately calculate your body fat percentage.
The Bioelectrical Impedance Analysis (BIA) is a simpler alternative to the skinfold method as it does not usually require a health care professional. This method measures the resistance to flow of electric current passing through our body. It is based on the principle that lean body mass presents high conductivity given the amount of water and electrolytes present in this type of tissue while fat body mass has low conductivity, and therefore, high resistance.
Based on these scientific principles, the BIA instrument will calculate the amount of water in a person's body, along with its intra and extracellular distribution to determine body composition. Keep in mind that since the instrument assesses the amount of water in a person's body, hydration level plays a major role in the results obtained.
For additional information, we recommend visiting the Centers for Disease Control and Prevention (CDC) website. There you will be able to find in depth information on how BMI values are used and what are some of the trends within the United States population.