Live Well – You and I and BMI

These days I’m attempting to walk a delicate balance between diving into obesity research, and framing everything I say in a size positive-way. It’s not easy. We keep hearing about a worldwide obesity epidemic. With it there is a slew of health problems both on a personal and a public health level, as well as size-related discrimination. Bullying, depression, unemployment, guilt, and self-loathing are part and parcel with obesity.

Here’s what I want you to know: size does not equal health.

Current World Health Organization standards use the Body Mass Index (BMI) to classify people according to a height to weight ratio. A BMI of 18 – 24 is considered ‘healthy’, 25 – 29 is ‘overweight’ (I’ve heard this definition is changing to ‘pre-obese’), and a BMI of over 30 is considered obese.

But. BMI does not take body composition into account.

Take, for example, hockey players. If you go onto the website of any NHL team you can find the height and weight of every player listed there. I spent a few minutes plugging info from some of the star players into a BMI calculator, and every single one of those strapping, fit lads was ranked as either overweight or obese. Clearly they’re not.

BMI is an excellent tool for tracking obesity, but it is way too blunt to be applied to individual health. And get this; a massive study was done following over 20,000 men which examined the relationship between fitness (measured by a VO2 max test) and fatness (measured by BMI) and the data showed that you were more likely to die from a cardiovascular event if you were lean and unfit than if you were fat and fit. The authors concluded that the heath benefits of being lean were limited to those who were lean and fit. I don’t know about you, but for me that’s motivation to get moving!

On the flip side, BMI is the dominant risk factor for type 2 diabetes; with a BMI of over 30 there is an 80% probability of developing the disease. However, a sizeable number of ‘normal weight’ people also develop the disease, and new research is showing that diabetic patients of normal weight are twice as likely to die as those who are overweight and obese. Similar findings have been documented in patients with cardiovascular disease, heart failure, stroke, high blood pressure, and kidney disease.

Why this happens isn’t really certain at this point. There are a number of hypotheses including genetics, obesity being protective during illness due to the body having extra energy it can use, and flawed assessment methods (BMI doesn’t take into account body composition or metabolic abnormalities). Fitness is also an important factor. According to a recent study at the University of Sydney, regular aerobic exercise may not result in weight loss, but it does decrease fat in the liver, where it possibly does the most metabolic damage.

So, lets not get hung up on numbers, but nor should we ignore them completely. Eat a balanced diet of nourishing real food, and move your body. I’m super excited about some upcoming Live Well guest posts from a couple of my favourite fitness experts, and I’ll be writing more about finding balance in your diet. Stay tuned!


  1. Kat says

    Thanks for summing up all that confusing information. The batteries died in the scale last month and we haven’t replaced them, choosing instead to focus on activity and happiness (what a novel concept!) rather than the number on the scale. It’s great to read reinforcing blogs like this one.

  2. Ceri @CucinaCeri says

    Likewise – a really well written and interesting post. I threw away the scales years ago, having spent a lifetime worrying about BMI and the like, which is confusing when you’ve spent time in the gym replacing fat with muscle. I much prefer to go on the way clothes fit (and occasionally test fat %.. if I can stomach the results!). Looking forward to reading more!

    • themuffinmyth says

      Thanks Ceri! I had my fat % measured years ago when I worked at a facility with a fitness lab and they did hydrostatic (under water) weight measurements. I’ve got no idea what it is now, but I don’t really care. I do weigh myself once a week (and only once a week) which is an old habit from my weight watchers days, but I try not to stress out about the numbers.

  3. Kathryn says

    This was such an interesting post, thank you so much for sharing. I’ve taken to discounting BMI because it seems to be so inaccurate but it’s interesting to see that it is a predictor of some health problems and there are some really interesting (and worrying) patterns emerging from some of the research. I look forward to seeing more posts in this series.

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