You’ve more than likely heard of the Body Mass Index (BMI) before – but what do you know about where it came from and its accuracy in predicting health outcomes?

Keep reading to find out what the evidence says! I KNOW you’ll be TOTALLY SHOCKED!

A timeline of BMI

1800’s

BMI was invented nearly 200 years ago by Belgian mathematician Adolphe Quetelet for the purpose of statistically analysing populations. His work focussed on identifying characteristics of “the average man” and studying patterns among groups of people.

In the case of BMI, Quetelet’s goal was to collect information about height and weight of the population to find the mean within it. It was with this purpose in mind that he developed “Quetelet’s Index”, now known as BMI. Quetelet stated that his equation could not and should not be used as an assessment of individual health status.

1900’s

Weight wasn’t considered a health indicator until the early 1900s, when life insurance companies in the U.S. began to compile tables of height and weight to determine how much to charge potential policy-holders.1 These tables were developed by actuaries trained in risk-assessment, and were based on the self-reported (read: inaccurate) heights and weights of people who held life insurance policies during a particular period of time.

For these tables, weight and height were the only factors considered – age, gender, ethnicity and other important characteristics were not taken into account.

The 50’s

Despite being poorly designed and inaccurate, the tables were adopted by physicians in the 1950s and 1960s to evaluate the health of their patients - and BMI entered the doctor’s office.

The 70’s

In the 1970s, researcher Ancel Keys (of ‘Starvation Study’ fame) undertook a study to determine the most effective measure for measuring body fat.2 He and his colleagues compared three measures: height to weight (i.e. Quetelet’s Index), skin fold measurements, and underwater weighing. They found that that Quetelet’s Index was “slightly better” than the other options, with a reliability of about 50% - in other words, the measurement only correctly diagnosed “obesity” about half of the time. It was by Ancel Key’s in this study that Quetelet’s Index was renamed Body Mass Index, or BMI.

In the early to mid 1980s that definitions of “overweight” and “obesity” began to be tied to BMI.

The 90’s

Then, in 1995, the World Health Organisation published a report recommending that the BMI thresholds for what was considered “overweight” and “obese” be lowered. This report was primarily created by an organisation called the International Obesity Task Force, who were funded by several pharmaceutical companies that produced weight loss drugs.3 By lowering BMI cut offs, the number of people who believed they needed to lose weight increased by millions overnight. This led to an increase in sales of weight loss drugs, thereby creating a surge in the profits of the pharmaceutical companies who paid for the report - yet another example of the diet industry creating insecurities and then profiting from the promise of “fixing” them.

The Present

Since then, BMI has been used faithfully by doctors and other health professionals as an objective and scientific assessment of health for most of the 21st century so far. But it’s time for that to change!

THREE REASONS WE SHOULD NO LONGER USE BMI AS A PREDICTOR OF HEALTH

So we know that BMI’s beginnings were indisputably dubious; but if that’s not reason enough to move away from BMI, let’s have a look at what the research says:

1. BMI cannot be applied to the wider population

When Quetelet collected the anthropometric information to form the basis of BMI, he did so from a group of white European men, without taking into account the huge variations in healthy body weights of different genders and ethnic backgrounds. 

For example, research has found that BMI overestimates health risks in Black populations and underestimates them in Asian populations.4,5

BMI also cannot differentiate between fat mass and muscle mass, meaning that a person with a large muscle mass will register as having an “unhealthy” body. BMI is also inaccurate for people of varying heights, as it divides weight by more in shorter people than in taller people, giving the impression that taller people are in larger bodies than they actually are.

Diversity is valuable (and inevitable!) and BMI is far too simple to account for this.

2. BMI is an inaccurate predictor of health

BMI is used with the intention of providing information about how at risk of illness a person is – but it doesn’t do this well!

One study that demonstrates this is a 2016 study into the cardiometabolic health of 40,000 people with a range of BMIs. Their results found that 30% of participants in the “healthy” BMI range were actually metabolically unhealthy based on their blood pressure, cholesterol levels and inflammatory markers. Additionally, almost 50% of “overweight” participants and almost 30% of “obese” participants were metabolically healthy based on the same measures.6

Additionally, a systematic review of 97 studies into mortality rates found that people within the “overweight” BMI category actually lived the longest!7 And that people in the “grade 1 obesity” category (BMI 30-35) had similar mortality rates to people within the “healthy” category.

In other words, despite its intention, BMI is actually a pretty poor predictor of health.

3. Weight cycling within a “healthy” BMI has worse health outcomes than maintaining your weight at an “overweight” or “obese” BMI.

Weight cycling (losing and gaining weight repeatedly) causes significantly poorer health outcomes than simply maintaining a higher weight. A study of 6.7 million people found that those with the greatest fluctuations in weight had a 53% higher risk of death from all causes than those whose weight remained stable – regardless of whether that stable weight was within a “healthy” BMI or not.8 This is thought to be related to the strain that weight fluctuations place on the heart, blood vessels, kidneys and nervous system.

There is even research that shows that weight cycling may account for all of the negative health outcomes associated with a higher BMI.9

In other words, it’s time to get off the diet cycle and work towards finding your healthy set point!

ASSESSING AND IMPROVING HEALTH WITHOUT THE BMI

If we know BMI is an inaccurate way of predicting the health status of individuals, how are we supposed identify when someone is at risk of poor health?

Instead of using weight, the current best-practice is to collect information such as pathology, vital signs, clinical symptoms, family history, environment and so on give a more accurate and holistic view of a person’s health.

And what about improving your health? That’s where HAES comes in!

Health At Every Size (or HAES) is a health-promotion model that focuses on implementing healthy behaviours rather than manipulating weight. Instead of fixating on achieving “healthy” BMI, it is far more beneficial to improve health-promoting behaviours, such as nutrition intake, movement, tobacco and alcohol use, sleep, stress, bowel health and more!

If you want to let go of BMI and find a healthier life without trying to shrink your body, that’s where Ari comes in! Explore her offerings to determine what will align best with your needs – whether that’s one-on-one coaching, workshops or a self-paced course, you can learn more here.

Let’s connect!