Reinforcing the Truth: BMI Lies

Refreshing an old topic: BMI

This is not really new information, but it’s worth addressing again. BMI lies. Regularly. In a few ways, actually. And it’s probably better to monitor “central obesity” — the fat we carry around the mid-section — because that is more closely related with health hazards. So let’s discuss:

BMI, that would be your “body mass index”, is normally used as a tool to assess your general health. It takes your total weight (in kilograms), and divides it by your height (in meters) squared. It’s just trying to answer the question: is your total mass appropriate given the size of your body?

BMI calculation

But is it equipped for this? BMI was originally developed in the early 1800’s to study growth patterns in adults, and wasn’t adopted as an obesity measure until the World Health Organization picked it up in 1995. It seemed like a simple, easy to understand tool as a reference for a person’s general health status — and it is! But it’s flawed too.

Santa BondWe now understand that BMI has a number of issues. Trying to distinguish between James Bond and Santa Claus? BMI sees the same person — no help there. Revamping your lifestyle to lose body fat but gain muscle? BMI is not your friend — it may go unchanged. And (perhaps most importantly), looking for support that your “pear-shaped” body is healthier than your friend’s “apple” shape? BMI again provides no support to your case.

Waist-to-hip ratio (WHR) does a nice job of teasing out some of these issues. WHR uses some math (sorry) to compare the size of your waist (usually at the top of your pelvis — about the level of your “belly-button”) to the size of your hips (usually at the level of your hips — the “greater trochanters”). “Normal”, in this study, was defined as a WHR of 0.89 for men or 0.80 for women, and “obese” was defined as a WHR of >1.0 for men or >0.89 for women.

WHR calculation

The nice thing about WHR is that it is a relative measure of your size, it should change as you change your body, and it distinguishes between general body size and increased size around the middle.

It also appears to be a far-better predictor of health issues than BMI too. The study that spawned the news article linked at the beginning, which spawned this posting, identifies that “central obesity”, especially in men, is a far better predictor of health issues than BMI values. This is especially true for men with “normal” BMI values, but unhealthy WHR values — people who might otherwise identify themselves as healthy.

Based on their analyses, the authors determined that for two men of average BMI, one with central obesity and one without, there is an 87% increased mortality risk for the man with central obesity. Yikes. Results showed that similar findings were recorded when comparing “average” BMI men with central obesity to “overweight” or “obese” men with no central obesity — the central obesity certainly appears to be the major player!

To be clear: WHR is also a flawed measure which needs to be considered as a part of a health assessment rather than in isolation. These tools merely provide a piece of information about a person’s well-being — but the more pieces we collect, the more we understand. So using any single tool on its own is generally inadvisable.

In Conclusion
  1. BMI lies
  2. WHR is a better predictor of poor health
  3. Increased central obesity predicts poor future health more than increased total BMI
  4. WHR lies too — it just does so less than BMI

Dr. Jim Gilliard is a chiropractor in Burlington, ON — if you have questions, comments, or wish to book an appointment, contact him at your convenience by leaving a comment below, visiting his website, via email at drjimgilliard@gmail.com, by phone at (905) 634-6000, or in person at Endorphins Health and Wellness Centre.


Primary Reference:
  1. Sahakyan KR, Somers VK, Rodriguez-Escudero JP, Hodge DO, Carter RE, Sochor O, et al. Normal-Weight Central Obesity: Implications for Total and Cardiovascular Mortality. Ann Intern Med. 2015;In press:1–11.

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