The myth of the Body Mass Index (BMI)

doodle_magnifying_glassAlmost everyone has heard of the Body Mass Index (BMI). It is one of the common metrics doctors use when judging how healthy we are. Schools calculate it to identify children who are “obese.” You can find it commonly discussed in all kinds of media.

But, what exactly is the BMI and what does it mean to our health?

The BMI is a calculation of height and weight in relation to each other. The calculation is: weight / height². If using metrics (kilogram / meter²) it’s as simple as that. If you’re using English or Imperial measurements (pound / inches²) then you multiply your total by 703.

The range of values is categorized according to particular standards, and labels are given to the resulting categories.

Current guidelines are:

  • Underweight <18
  • Normal weight 18-25
  • Overweight 26-29
  • Obese 30+

First calculated by Adolphe Quetelet in 1830, a Belgian mathematician, to try to describe the “average man”, it was meant to be used as a statistical device, not as an individual health indicator.The main thing the BMI does not show is how healthy or unhealthy that person may be. For example, Tom Cruise has a BMI of about 26, in the overweight category, and Sylvester Stallone is considered obese with a BMI of 37. These two stars spend a lot of time and money to stay in shape and healthy – so we need to go beyond BMI to understand health, at least in these cases.

Weight is a combination of fat, bone, muscle, other tissues, and water.

The exact amounts of each are different from person to person and people of very different body compositions may have the same BMI. In other words, three different people may have the same BMI, but they may have different amounts of fat or muscle or be different heights or weights.

According to Linda Bacon in Body Respect, when she investigated why the United States lowered the BMI standards in 1998, in the absence of supporting research, she discovered:

“…that they got a lot of pressure to conform to international standards…the [World Health Organization] relied on the International Obesity Task Force (IOTF) to make the [BMI] recommendations. At the time, the two biggest funders of the IOTF were pharmaceutical companies that had only weight-loss drugs on the market.”

In the research, BMIs in the extreme ranges, very low or very high, are correlated with poorer health outcomes. Clear enough, right? Maybe not! Further analysis shows us that this simple correlation does not mean high BMIs themselves are the cause of poor health outcomes.  Fitness, for instance, is a huge indicator of positive health outcomes, regardless of BMI.

The fact that we continue to use BMI to gauge individual health is a travesty. Health outcomes would improve significantly if BMI was completely thrown out and a weight-neutral emphasis on healthy habits was employed by health professionals. This is one of the reasons I practice Health at Every Size®. In my practice, I’ve learned that focusing on healthy habits has a much greater chance of creating states of wellness than intense focus on weight loss.

Written by DeAun Nelson


My philosophy is that we are all in this together. If you have compassion and care for yourself, that compassion and care will extend to those around you. Naturopathic medicine is all about treating the whole person. In my mind, this means treating not just individuals, but communities. We all have incredible bodies that do incredible things, even when we are suffering. We live, breath, laugh, and love. You are an important being who deserves respect and judgement-free care.