BMI is Not a Good Indicator of Health
Body mass index (BMI) is a commonly used metric of health assessment. Currently, BMI is used to diagnose “obesity” and to determine if people qualify for certain medications, surgical procedures, and other health treatments. But does body mass index actually tell us anything about a person’s health?
If you’re new here, hello and welcome! My name is Hannah and I am a non-diet dietitian here to help you improve your relationship with your food and finally find food freedom.
In this blog we will cover:
What is BMI?
The history of BMI
The issues with BMI
Better alternatives to assess health status
What is BMI?
Body mass index (BMI) is a ratio of height to weight. More specifically, it is your weight in kilograms divided by your height in meters squared.
Based on this equation, BMI is used to classify individuals as “underweight”, “normal weight", “overweight”, or “obese”. It’s important to note that I put these terms in quotation marks because terms such as “overweight” create the assumption that there is a correct weight that people should be at, and it you are above it, you are abnormal or different.
Bodies are beautifully diverse and being classified as “overweight” on BMI standards does not mean that your body is “wrong” or “unhealthy”.
All that said, these are the current BMI classifications:
Underweight: <18.5
Normal weight: 18.5-24.9
Overweight: 25.0-29.9
Class 1 Obese: 30-34.9
Class 2 Obese: 35.0-39.9
Class 3 Obese: >/= 40.0
The history of BMI
BMI was founded in the 1830s by a Belgian statistician, sociologist, astronomer and mathematician by the name of Lambert Adolphe Jacques Quetelet. It was known then as the Quetelet Index and was created due to Quetelet’s interest in finding “l’homme moyen,” or “the average man”.
Quitetlet explicitly said that BMI could not and should not be used to indicate the level of fatness in an individual, yet BMI is currently used to diagnose if an individual is underweight, normal weight, overweight, or obese, which is then used to estimate an individual’s risk for disease. This has become increasingly controversial as there is no evidence that shows that an individual’s weight causes health issues. There is correlation, but correlation does not equal causation. You can read more about that here.
The issues with BMI
BMI was not used as the standard for diagnosing “obesity” until the 1980s. It is frequently used because it is inexpensive and simple to calculate. However, BMI only takes height and weight into account, and there are MANY more indicators of health than just an individual’s weight. Providers that abide by BMI as a diagnostic tool tend to assume someone’s behaviors and health status based purely on their body size.
BMI does not consider body composition
When you weigh yourself (or when you see someone else’s weight), you do not know how much of this weight is muscle mass, fat mass, water weight, or weight of all the organs that humans just so happen have. Unless you are also assessing body composition, body weight tells us nothing aside from a person’s mass on planet Earth.
Bodybuilders and others with relatively large amounts of muscle mass are often classified as “obese” based on BMI standards, simply because their muscle is quite heavy. Does this mean that these people are unhealthy or have a chronic “disease of obesity”? Maybe, maybe not. It’s not as simple as a number on the scale.
BMI is rooted in race bias
BMI was based off data from a group of white European men. News flash - we are not all white European men. Again, bodies are diverse. How boring would it be if we all looked the same?
The creation of BMI is based on a very poor sample group that cannot be used to generalize health information for the entire population without proper representation.
BMI sets unrealistic weight standards for both men and women
Speaking of differences in body size and composition, there are also physiological differences between biological men and biological women. Again, we aren’t all meant to weigh the same.
These standards can create disordered relationships with food and bodies. I have worked with many people (both men and women) who have expressed feeling guilty for not having a body size within a “normal” or “healthy” BMI. This can result in chronic restriction and dieting as an attempt to obtain a goal weight.
BMI can result in dismissal of health conditions
Some medical providers will see a patient in the “overweight” or “obese” category and immediately tell them to lose weight without taking into consideration any other measurement of health. The say things like “If you just lose weight, your medical condition will go away”. Many people at a higher BMIs will avoid going to the doctor because of this weight stigma.
I have heard countless stories from clients who have gone to their doctor for a sore throat and left with only the advice to go on a very low calorie diet. Healthcare is not true care when it is rooted in fat phobia and anti-fat bias.
BMI specifications favor pharmaceutical companies
In 1998, the BMI ranges changed overnight, making millions of people suddenly “overweight”.
The cutoff for being considered “normal weight” used to be 27 for women and 28 for men, but it was lowered to 25 for all in 1998. The decision was based on a report funded by pharmaceutical companies that make weight loss drugs. If more people – and more doctors – thought that patients were “overweight”, and need to lose weight “for health”, then they could sell more weight loss medications.
Better alternatives to assess health status
Rather than using BMI or simply looking at a person’s body and making assumptions about their health, I vote we dig a little deeper. While we’re at it, we also need to remember that health looks different for everyone and that health is not a moral issue i.e. you are a not a better person for being “healthy” and a worse or less deserving person if you are “unhealthy”.
Here are a few metrics of health that we can (and should) use beyond just body weight.
Body composition
Lab values
Dietary recall
Mental health and stress management
Sleep quality and quantity
Relationship with food
Access to food
Body image
Bottom line
BMI is provides very little insight to health status. If you do not fit within the “normal” BMI classification, that is okay. The size of your body does not paint the full picture.
