Calculating someone’s BMI is the most common way to find out if they are a healthy weight, but a doctor has slammed the tool.
Dr. Karan Raj, a UK-based NHS surgeon, claims the calculator “should not be used” as an isolated tool to predict health risks.
What is Body Mass Index?
Body Mass Index (BMI) is a widely used medical method to measure if someone is a healthy weight for their height. It’s calculated by dividing an adult’s weight in kilograms by their height in metres squared, the NHS explains.
The resulting number determines whether you are underweight, healthy weight, overweight or obese:
- Below 18.5 – underweight
- 18.5 to 24.9 – healthy weight
- 25 to 29.9 – overweight
- 30 to 39.9 – obese
- 40 or above – severely obese
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These numbers are slightly different for people of Asian, Chinese, Middle Eastern, Black African or African-Caribbean descent.
The idea was first devised by Belgian astronomer and mathematician Adolphe Quetlet between 1830 and 1850, but the modern term Body Mass Index was coined by physiologist Ancel Keys in a July 1972 paper in the Journal of Chronic Diseases.
Since then, it’s been adopted by medical professionals across the globe and the World Health Organization (WHO) recognizes it as an effective way of determining whether someone is a healthy weight.
Doctor slams BMI
However, Dr. Karan Raj slammed the idea in a viral TikTok video, asking: “Why are we still using BMI as a measure of health?”
“Clearly you can have two people of the exact same BMI bit wildly different health statuses,” he said, suggesting that the tool is not helpful.
The doctor explained that BMI doesn’t account for body fat composition, muscle mass, waist circumference or any health behaviors. BMI measures whether a person is carrying too much weight but not too much fat. For example, people who have a lot of muscle, like professional sportspeople, can have a high BMI without much fat.
He added that the body fat measurement has a “racial bias” as different ethnic groups have varying degrees of risk for health conditions at the same BMI. People of Asian descent tend to carry a higher body fat percentage than Europeans, so have a bigger risk of conditions like heart disease and diabetes at a lower BMI.
The doctor said that Body Mass Index is useful across big populations, and can help to highlight an “at risk population” that may benefit from lifestyle. However, it “should not be used in individual cases as an isolated tool to predict someone’s health risks”.
In his opinion, no singular metric should be used to determine overall weight-related risks to health.
Tackling obesity
While the tool does have limitations, it is one of the only ways to diagnose obesity, which can result in many health issues.
According to the latest WHO figures from 2022, 1 in 8 people in the world were living with obesity. 43% of adults aged 18 years and over (2.5 billion) were overweight and 16% (890 million) were classified obese.
People living with obesity are at risk of many conditions including type 2 diabetes, coronary heart disease, some types of cancer including breast and bowl, and stroke, the NHS explains.
Dr. Karan Rajan, better known as Dr. Karan Raj, is an NHS Surgeon with more than 10 years of experience, and a Clinical Lecturer at Imperial College London and the University of Sunderland.
