Are we giving too much ‘weight’ to body mass index?


Chances are, if you are conscious of your weight and health, you will know what the body mass index (BMI) is and you will know whether you are in a healthy range, according to the index.

No? Let us explain. According to Health24, BMI is a simple index of height-for-weight, and is commonly used to indicate overweight and obesity. It is calculated as follows:

BMI is calculated by dividing weight in kilograms by height in metres squared. For example, if you are 1.65m tall and weigh 85kg: weight ÷ height squared = 85 ÷ 1.65 x 1.65 = 85 ÷ 2.72 = 31.25. The result is a BMI of 31.25.

 According to the BMI, between 18 and 25 is a healthy weight; between 25 and 30 is overweight; and anything over 30 is obese.

The problem with BMI

Although the BMI is a simple mathematic formula to use as a guideline, people have been questioning its accuracy. If you’re extremely muscular and your number is over 30, would you still be classified as obese?

While a number can be a good guideline, it has often been said that doctors and medical practitioners cannot solely diagnose patients as “obese” because of a number. They would need to take factors such as medical history, body fat percentage, muscle-to-fat ratio and overall fitness and diet into account.

Let’s take a theoretical case: A 30-year old woman is 1.69 m tall and weighs 72 kg. She eats healthily and exercises five times a week, including strength exercises and marathon training. Her body fat percentage is 20% and her waistline is within the healthy region of less than 80cm in circumference.

If we do the maths, her BMI is 25.21 which is technically overweight – a term you would definitely not use if you saw her in person.

This also means that many professional sportsmen would be placed into the obese category, as their muscle density is greater than that of a regular person.

Why BMI is not that good

According to research, nearly half of the people classified as overweight or obese are actually healthy when other factors are taken into account.

And Robert Shmerling from Harvard’s Health publication wrote in this article that BMI itself cannot measure health, but is simply a number representing a person’s size.

But size still matters

While BMI might not be the be-all and end-all of health, we should keep in mind that a healthy body weight lowers your risk for chronic illnesses and other medical problems.

Doctors and health professionals will still use BMI along with your medical history to determine whether you are overweight or obese, but you will get a more accurate analysis by having your overall body fat and muscle mass measured as well, according to

A healthy, happy medium

Instead of obsessing about the numbers too much, you can maintain a healthy body weight by eating a balanced diet and doing regular exercise without quick fixes or fad diets. It is also important to monitor your weight as you grow older and to realise that your metabolism is slowing down.

This article is provided through a sponsorship from Pfizer in the interests of continuous medical education. Notwithstanding Pfizer's sponsorship of this publication, neither Pfizer nor its subsidiary or affiliated companies shall be liable for any damages, claims, liabilities, costs or obligations arising from the misuse of the information provided in this publication. Readers are advised to consult their health care practitioner for specific information on personal health matters as this is not the intention or purpose of the publication. Specific medical advice or recommendations on the clinical management of patients will not be provided by Pfizer. In this regard Pfizer does not support the use of products for off label indications, nor dosing which falls outside the approved label recommendations and readers must refer to the Package Insert of any product for full prescribing guidelines. 

We live in a world where facts and fiction get blurred
In times of uncertainty you need journalism you can trust. For only R75 per month, you have access to a world of in-depth analyses, investigative journalism, top opinions and a range of features. Journalism strengthens democracy. Invest in the future today.
Subscribe to News24
Voting Booth
Have you entered our Health of the Nation survey?
Please select an option Oops! Something went wrong, please try again later.
32% - 9428 votes
68% - 19893 votes