Top 3 Weight Loss Myths: Myth Two
We Should All Be a BMI of Less Than 25
There is a lot of focus by society, and unfortunately even in the medical community, on BMI.
The magic point at which apparently we can be assured that an individual is perfectly healthy.
But is BMI all it is cracked up to be?
What is BMI?
As per the WHO, ‘Body mass index (BMI) is a simple index of weight-for-height that is commonly used to classify overweight and obesity in adults. It is defined as a person's weight in kilograms divided by the square of his height in metres (kg/m2).’
The ‘normal range’ for BMI is 18-25kg/m2. Overweight is defined as 25-30kg/m2 and obesity over 30kg/m2.
Where did it come from?
BMI as a measure was invented in the 1830s by a Belgian mathematician, Lambert Adolphe Jacques Quetelet. It was developed with the purpose of finding “l’homme moyen,” - ‘the average man’ in a quest to determine patterns of deaths at a population level. It was not developed to determine the health of an individual.
In 1972 a Physiologist named Ancel Keys took BMI and proposed that it be used to relate obesity and body build to disease and death rates.
So what does BMI do?
Essentially it compares your size to the size of the average white man living in Belgium in the 1830s.
Measuring BMI is quick and easy. When individuals fall far outside the average, it does give some idea of an increased risk of weight related issues.
What does BMI not do?
BMI doesn’t take into account your race, age, gender, genetics, muscle mass, lifestyle factors - diet and exercise levels, smoking, alcohol. It doesn’t take into account your cholesterol or blood sugar.
In an article in the International Journal of Obesity, BMI classification was compared with health. Nearly half of overweight individuals, 29% of obese individuals and even 16% of those who had a BMI of over 35 were found to be metabolically healthy.
And 30% of normal weight individuals were cardiometabolically unhealthy.
What does this mean? That BMI was wrong in predicting ‘health’ in more than 30% of individuals.
The Dangers of Just Using BMI
When we use BMI to determine health, it is wrong a lot of the time!
It can distract from the steps we should take - healthy eating, enjoyable movement, more sleep, less stress - to a vague objective of weight loss
It is demotivating - getting to a BMI of 25 is out of the reach of many individuals
It is a distraction - weight is not the only factor involved in many medical issues - such as joint pains, infertility, PCOS, and higher weight does not preclude individuals from having an eating disorder
It sets an often times unattainable body ‘ideal’ - especially damaging for individuals not included in the original calculation of ideal BMI (women, people of colour)
What should we do instead?
Take BMI with a grain of salt - it is easy to measure, but may get it wrong a lot of the time
Ask your doctor to use markers than just your weight to determine health - and who would benefit from what interventions for their health
We should not use getting to a BMI of 25 as a goal for weight loss - the goal should be specific to you.
You are not your BMI - most times there are a lot of other things that we can do as well of or instead of weight loss to improve any medical issues and maximise your quality of life.
