Is BMI an accurate predictor of Health?

Is BMI an accurate predictor of Health?

We all consume fat in the form of food that we eat and our body stores it. The fat content is too high or too low is based on the fact that where our body stores it. In both cases there is a danger of illness or disease, So how do we measure this fat content? Well, it can be done using a Dual-energy absorptiometry (or DXA) machine which scans and provides us with this information. 

Another method that is very handy; is "calculating BMI"

BMI stands for Body Mass Index and is one of the most well-known and most used ways to measure body composition. So now let us understand how does it calculate our health status and also is it the only criteria to judge our health and how effective it is as an indicator for our health.

History of BMI 

Let’s start with the history of BMI. It was first developed by Adolphe Quetelet from Belgium during the 19th century. During the 1970s and based especially on the data and report from the Seven Countries Study, researchers noticed that BMI appeared to be a good proxy for adiposity and overweight-related problems. Since then it is in use. 

How to calculate BMI

Mathematically, BMI is calculated by applying a simple formula i.e.

BMI = weight (kg) / height (m2)

The BMI value calculated acts as a measurement on the below-mentioned chart and determines your category for people aged over 20 years

How does BMI help us? 

BMI is quick to calculate, affordable and easily accessible hence allowing health professionals to screen a person’s health profile. 

BMI is used to assess risk for diseases, especially heart disease and diabetes. 

As BMI increases, so does the risk of developing these and other weight-related diseases, including stroke and some cancers.

A BMI >25 means that the person is at a high risk of heart disease, diabetes, arthritis, mental health and cancer 

While BMI < 18.5 means that the person is undernourished or malnourished and may have immunity issues, respiratory problems, digestive disorder, bone mineral deficiency, cancer 

BMI is intended for adults only, as children and adolescents are constantly growing. This makes it difficult to have set values for BMI cut-offs for young people. However, in adults who have stopped growing, an increase in BMI is usually caused by an increase in body fat. 

So if BMI is able to point out this risk then can we say that BMI is the right indicator to assess the health condition of a person? 

To begin with this there is an interesting fact that Adolphe Quetelet had stated that BMI should be studied for giving a snapshot of a population’s overall health rather than for an individual. Many scientists and leading research organizations also resonate with the same thought because of certain limitations.

There are several factors that are not covered under BMI like : 

1. Body Fat Percentage –  Body Fat Percentage calculates the percentage of body fat in the body. BMI has a limitation in that it does not distinguish fat from muscle. For example : 

BMI will exaggerate the body fat value for : 

      • People who are into bodybuilding will have a lot of muscle bulk hence a high BMI but are not overweight

      • Professional athletes because of their greater muscle mass 

      • Pregnant women 

BMI calculations will under evaluate the amount of body fat for:

      • Elderly people 

      • People with a physical disability, who are unable to walk. They have muscle wasting hence their BMI will be lower

BMI is also not an accurate indicator for people with:

      • Eating disorders like anorexia nervosa

      • Extreme obesity

2. BMI does not differentiate between different ethnicity of people as it was observed by WHO in 2004 that Asian people who had a higher risk of Type 2 diabetes had lower BMI. Hence one size fits all cannot be the strategy for patient care.

3. BMI does not tell anything related to where the fat is stored. To explain it fat on the thigh and butt region will not give a clear indication about possible cardiovascular risk as compared to the fat in the upper body (visceral fat).

So if BMI is not the candidate for being the right indicator for health then what should be the right predictor for health?

Waist circumference: Many consider Waist circumference as a better indicator of increased disease risk.

Fat or potbelly irrespective of body size implies that there is a greater risk of obesity-related complications. If the waist circumference is more than 90 cm in men and 80 cm in women then they are identified to be at high risk 

Reference : 
https://www.insider.com/is-bmi-accurate
https://www.betterhealth.vic.gov.au/health/healthyliving/body-mass-index-bmi
https://theconversation.com/body-mass-index-may-not-be-the-best-indicator-of-our-health-how-can-we-improve-it-143155
MJ 2016; 355 doi: https://doi.org/10.1136/bmj.i5855 

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