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What do you know about the Body Mass Index, otherwise known as the BMI? It was drilled into my head during school as a way to categorize people based on their height and weight. There is a sweet spot called “normal”; otherwise, you can fall too high, or too low on the index. Falling outside the “normal” range comes with health risks….or so I was taught. But the more I looked into this tool, the less reliable it seemed. Does it really identify health risks? How accurate is it? Should we really be putting so much weight behind the BMI (pun intended).
Before we dive into the history of where the BMI even came from, here’s a quick reminder:
This is the BMI (can you tell it was developed in Europe with kg and meters?- ha!)
BMI = weight (kg) / height2
For the US: BMI = (weight (lb) ÷ height2) x 703 (inches)
Surely, it was designed with the best of intentions.
The BMI was developed in the 1830’s by Lambert Adolphe Jacques Quetelet- a Belgium astronomer, mathetitican, and statistician. It was developed as a quick way to assess the general population for statistical purposes, NOT as an indicator of health and was originally called Quetelet’s Index.
Takeaway: A smart guy who has nothing to do with the medical field developed the BMI for statistical purposes, NOT for health purposes.
So if the inventor of the formula didn’t intend for it to measure health, what happened?
Insurance companies (notice: NOT medical doctors), that’s what happened! They noticed that being larger in size was possibly linked to a decrease in lifespan. So, they needed a quick and easy way to quantify the risk and to determine what to charge potential policyholders. Insurance companies began to create height/weight tables using Quetelet’s Index. Their tables were based primarily on white men. In time, physicians began to use the tables to evaluate their patients’ health.
Takeaway: Insurance companies were using it to make more money.
Ok, weird, so where did “The Body Mass Index” come from?
The BMI officially got its name in 1972 after a study done by researcher Ancel Key’s and his colleagues. The study was to find an easy and cost effective way to measure body fatness. In theory, body fatness is linked to health concerns; the more body fat you have, the higher your risk. On the flip side, you can have too little body fat which comes with its own risks. The study compared skin calipers (where you pinch your fat and measure how much is being pinched), water displacement (where you are submerged underwater with the displacement of water being different for fat vs muscle) and the BMI formula. Skin calipers took some time and effort and the subject to be present while the underwater weighing was, well, not really convenient or cost effective at all. It was found that the BMI formula was just as effective for measuring body fatness, or obesity as the other two options. They all measured body fatness correctly about 50% of the time, aka, they were all wrong about 50% of the time as well. Not great. But not any worse than the other two options, and a little quicker and easier.
Takeaway: The BMI is the “best” way to measure body fatness of the not so great options. Additionally, it’s not very accurate (it’s basically a 50/50 shot of being correct)
But it has the categories of overweight, obese, etc, they have to mean something.
In 1993, the World Health Organization (WHO) assembled an Expert Consultation Group who developed the categories of the BMI: underweight, normal weight, overweight, and obese. These were published in 1995 for the world to use. Before this time, obese was not regularly used as a health term. One would think the terms were linked to health conditions. For example, you would think moving up on the BMI scale would put you more at risk for heart disease or diabetes. However, you would be wrong, the categories are based on nothing.
In 1998 The National Institute of Health changed the criteria for overweight and obese to match the criteria the WHO was using. Originally, people with a BMI of 27.8 (men) and 27.3 (women) or greater were classified as overweight. This label (and it was only one, you were either a “normal” weight or overweight) was based on a percent of the population, 85% of the population to be exact. However, when the US aligned with the WHO and made a BMI of below 25 a normal weight, millions of Americans now bumped up to overweight even if they didn’t gain a pound.
Takeaway: The categories of overweight, obese, morbidly obese, do not correspond to any health conditions or risk for disease. They are completely made up and have been changed overnight.
There are so many things wrong with the BMI, from how it was developed, to how it’s currently being used.
It was based on men, and only men. Women and children were not taken into account when gathering the initial information in the 1830’s. The policy holders for insurance were predominantly men, and the study done in 1972 was on men. No women or children were in the mix. Yet, it is used on women and children.
Speaking of children- this should in no way be used to evaluate them. Children tend to grow out, then up, then out, then up, making it a useless tool to label kids’ weight as normal or anything else, as they probably aren’t done growing yet.
It does not account for body composition. Muscle, fat, bone density, frame size, age, gender. None of it is taken into consideration. Just height and weight.
It is not linked to any type of health conditions. In fact, more research is being done saying that people in the overweight category may have better health outcomes. We don’t know yet. Better yet, research is showing that up to about 25% with a normal BMI can have underlying health conditions and about 30% of overweight or obese people are perfectly healthy.
Bottom line, the BMI is not all it’s cracked up to be. Say you’re 5’7” and weigh 191 pounds. If you gain one pound, you now moved from the overweight to the obese category. So what? Your health didn’t change with one pound, but your label did. It doesn’t account for muscle mass, bone density, or frame size. It doesn’t take gender or ethnicity into account (and side note, women need more body fat than men). Plus the categories are COMPLETELY MADE UP. Instead of forcing people into categories based on their height and weight (and literally nothing else), how about trying to look at the bigger picture, like blood work, blood pressure, family history, eating habits, exercise routine, sleep, and stress.
What are your thoughts? I’m finding it hard to find a situation where BMI would be helpful.
Stay Happy, Stay Healthy
This blog was written by Chris Henigan MS, RD, LDN, co-founder of Simple Start Nutrition. For more blog posts and nutrition information follow @simplestartnutrition on Instagram and Facebook. Also feel free to contact us, by visiting our website (simplestartnutrition.com) to schedule an appointment to discuss your nutrition related needs. We’re here to help.
References:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4890841/
https://www.medicalnewstoday.com/articles/255712#are-people-misclassified
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