What is BMI?

You may have heard of the term BMI before in relation to health, but what does it actually mean? BMI stands for Body Mass Index, which is essentially an indication of how healthy you are based on your weight and height. You, your GP, or other health professionals can use BMI as a measure of your current health levels. 

 

How Is It Calculated? 

Calculating BMI is a very straightforward process – for adults, the only two things needed for the calculation are height and weight. You can calculate your BMI manually or alternatively, you can use a BMI calculator which will do the calculations for you, you simply have to enter your information. It should be noted that for young people aged 2 – 18 years old, their age and gender must also be taken into account when calculating BMI. 

To manually calculate your BMI, you can use the following formula: 

 

weight (kg) / [height (m)]2  


OR


[weight (kg) / height (cm) / height (cm)] x 10,000 


To put it simply, you can just: 

  1. Take your weight (kg) and divide it by your height (cm)
  2. Divide this number by your height (cm) again 
  3. Then multiply that number by 10,000 
  4. Round this to 1 decimal place and that’s your BMI


For example: Someone’s weight is 67 kg and their height is 175 cm. 

  1. 67 / 175 = 0.38286
  2. 0.38286 / 175 = 0.00219 
  3. 0.00219 x 10,000 = 21.87755
  4. BMI = 21.9 

 

What Does My BMI Mean?

So now you’ve got your BMI, what does it actually mean? For most adults, the ideal BMI is between 18.5 to 24.9 as this is classed as the healthy weight range. 
 

Here are the different BMI ranges: 


Underweight – Below 18.5
Healthy Weight – Between 18.5 and 24.9 
Overweight – Between 25 and 29.9 
Obese – Between 30 and 39.9

 

How Accurate Is It? What are the Limitations? 

Although BMI can provide an indication of whether or not someone is of healthy body weight, it is important to note that BMI has its limitations and there are certain factors that should be taken into consideration. The following highlights some limitations:

 

Muscle – BMI doesn’t take body composition into consideration, so someone with a lot of muscle mass may have a high BMI which would put them in the ‘overweight’ or ‘obese’ range, even though they’re in good health. This is due to the fact that muscle is denser than fat so people with a lot of muscle such as bodybuilders and athletes, for instance, may be ‘heavier’ in theory but will actually be very healthy, despite what their BMI says.

 

Body Type – BMI also doesn’t take different body types into account and in particular, how fat is stored in each one. For example, there could be 2 different people who have the exact same BMI but one stores more fat around the waist area – this indicates that they are at higher risk of developing diseases such as heart disease and diabetes as the buildup of fat around this area is linked to higher blood fat levels and blood pressure due to the fat being around your organs. 

 

Ethnicity – Health risks can affect ethnic groups differently, so if there are 2 people who have the same BMI but are of different ethnicities, they may not necessarily be on the same level of health. For instance, Asians may be at higher risk of certain diseases, such as diabetes, at a lower BMI compared to other ethnic groups. 

 

It is important to remember that various other factors can affect health so BMI alone cannot always be taken at face value as an exact representation of how healthy you are. There are some instances whereby BMI shouldn’t be used as an indicator of health at all – e.g., if you’re pregnant (speak to your doctor or midwife if you have any concerns regarding your health or weight) or if you have or may have an eating disorder (please speak to your GP for health advice).

 

​​​​​​​​​​​​​​Quick Tips for Maintaining a Healthy Weight

  1. Stay active – Make sure that you’re doing exercise regularly, even if it’s just going for a walk once a day.
  2. Eat protein – Ensure that you’re getting enough protein in your diet.
  3. Stay hydrated – Remember to drink sufficient water every day. 
  4. Well-balanced diet – Try to eat a well-balanced dish for every meal. 

 

References

https://www.cdc.gov/nccdphp/dnpao/growthcharts/training/bmiage/page5_1.html

https://www.nhs.uk/common-health-questions/lifestyle/what-is-the-body-mass-index-bmi/

https://www.webmd.com/diet/features/bmi-drawbacks-and-other-measurements

https://www.bhf.org.uk/informationsupport/heart-matters-magazine/medical/measuring-your-waist

https://www.healthline.com/nutrition/maintain-weight-loss#TOC_TITLE_HDR_10