Body Mass Index and Weight: Why scales and ideal body weight are not your friend!

How many of us stepped on the scale this morning and scratched your head in disbelief?  Or inputted your height, and weight in one of those body mass index (BMI) calculators and almost flipped over in your chair when the readout said “Borderline Normal”, or “Overweight”?

I stepped on the scale this morning and weighed in at a handed 145 lbs so at five feet two and a half inches my BMI reads 25.7.  I’M OVERWEIGHT!  But don’t fear, I’m not here to talk about how to calculate your BMI but to actually say that we need to throw this measurement out the window along with people’s notions of what they believe is their ideal weight.

So why is BMI inaccurate and why do we still use it?

People use BMI because it’s easy.  All you need is height and weight and the formula and it spits out a number.  When we compare the number to an “Average” we get the following BMI categories (in kg/m^2):

  • Severely Underweight: less than 16.0
  • Underweight: from 16.0 to 18.5
  • Normal Weight: from 18.5 to 25
  • Overweight: from 25 to 30
  • Obese Class 1: from 30 to 35
  • Obese Class 2: from 35 to 40
  • Obese Class 3: over 40

Health Professionals still use this scale in order to determine a person’s general health status, but get this:  The data used to determine these categories was originally from a study in 1994 using 8550 males!  How relevant is this in our current day and age and does anyone else find it a little concerning that we are using data from only males?  The biggest issues are that BMI is not an accurate reflection of all the people of different weights and genetic backgrounds like I was saying in our previous blog about the genetics of weight loss, it also does not account for differences in bone density, body structure, muscles and age (we get shorter as we grow older even if our weight remains the same.)  There has been a lot of research in the past 10 years on how ineffective this  rating scale is, but for some reason it’s still prolific!

The point of concern is not necessarily people that are in the Obese classes.  The research has proven pretty sound regarding the effects of obesity on cardiovascular health and other diseases.  The general concern are people between the underweight and the overweight categories.  The research on these categories have shown that there is little statistic difference regarding cardiovascular health and potential for other diseases between them, even though the BMI categories claim that there is a difference.  The problems go even deeper though since our societal views on ideal body weight are strongly linked to BMI.  We see “Pretty” or “Beautiful” as a specific weight associated with BMI or ideal weight.  We as a society need to look at better functioning metrics for general health and loose the idea of what is considered to be idea, we are all unique so lets use measurements that reflect that.

Improvements in health should ideally be ratios and percentages since these are far more accurate than a measurement that bases itself against a standard like BMI and ideal body weight.  Body fat percentage and waist to height ratio are actually one of the more accurate set of measurement tools to determine health and also the potential for chronic illnesses.  We want to start seeing the percentages and ratios decrease as we exercise and eat properly.  Take note: we are moving beyond the normal weight loss metrics and into lifestyle management and prevention.  Let’s further simplify progress by eliminating body fat percentage as a regular method of determining change in health.  I suggest not using body fat percentage because most of our readily available measurement devices are pretty inaccurate (bio impedance scales and callipers) and the more accurate methods of measuring are quite expensive.  Grab your tape measure and lets get some waist to height ratios!

Measure your waist circumference horizontally one inch above your belly button (in inches) and divide by your height in inches.

Here’s how we read the Waist to Height Ratio:

  • If you are younger than 40, then anything ratio over 0.5 is critical.
  • If you are between the ages of 40 to 50 then critical values to see change are between 0.5 and 0.6.
  • If you are older than 50 then the critical value is 0.6.

Critical values mean that a person has a high chance of heart attacks, stroke, or other chronic illnesses.  Ultimately the whole point is to make sure that we stay below the critical ratios, and when we have achieved this we then look at focusing more on leading a healthy lifestyle.

We want to move away from achieving and ideal body into a functional and healthy human being.  Exercise and proper nutrition are part of leading a fulfilling life since they enhance our quality of life.  We are all unique so why strive towards the ideal when we should concentrate on who we are as individuals and as a community!

About Chris Tse

I’m a scientist turned owner of Blitz Conditioning, a Fitness Columnist at CBC Radio on Thursdays at 8:20 am, and owner of Tse Social Strategy. Follow me on Twitter or Read my full bio.


  1. Awesome! I like this new measurement system because it’s simple. (however, I’m definitely in the critical regime – 35/63 = 0.55 – whoops!). I wonder whether it is even possible for me to go below 0.5, which would be 31 inches when measured an inch above belly button. Perhaps this is a good target to focus on.

    • Hi Addie, thanks for the comment! Ultimately all of the measurements have their issues but, yes, it’s best to look at improving the whole body through healthy lifestyle changes and then the measurements are simply there as markers.

  2. Glad to see that Blitz has addressed this in a blog. This is something that has bugged me since my years of University, not just with BMI indexes but with IQ tests, and many tests used to measure or compare people against what the “standard” or “norm” is, or to try lump people into a category.

    Much of these tools were devised as one size all or designed for a specific population, and today, in many context, asking “what is specific” is pretty much asking to define what is “normal”.

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