Science and Tech
Feeling Fat? Don't Measure Your Weight Loss This Year With BMI

Marla Desat | 9 Jan 2015 16:00
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BMI, staging systems, and you

Measuring the height and weight of many people is easy and cheap, and BMI provides a great measurement to evaluate and track large populations like a country or a continent, but there are many other factors to consider when talking about an individual person's BMI and their health. When medical professionals evaluate whether a patient's weight warrants intervention, there are several factors to consider beyond BMI. AM Sharma from the University of Alberta Department of Medicine, and RF Kushner of the Northwestern University Feinberg School of Medicine, reviewed the limitations of BMI and proposed a staging system for obesity treatment in a 2009 paper. Staging systems use a variety of factors to describe a patient's condition, often including quality of life and the presence of related diseases or disorders, called comorbidities. Similar staging systems are already used for describing cancer progression, congestive heart failure, and kidney failure.

BMI chart

Sharma and Kushner argue that applying BMI to individuals has limited use for doctor's decisions, stating that "individuals with the same BMI value can have an almost twofold difference in total body fat, whereas conversely, individuals with the same amount of total body fat can present with a wide range of BMI." Sharma and Kushner advocate instead for including other risk factors when evaluating obesity, by including obesity-related risk factors (hypertension, diabetes, sleep apnea), physical symptoms (fatigue, aches and pains), psychological symptoms, and functional limitations. The paper presents a few case studies, pairing the WHO classification of weight with a stage rating ranging from 0 to 4. A woman with a BMI of 32 but no other risk factors would be classified by this system as Class I, Stage 0, and does not need medical intervention, while a man with a BMI of 36 who also has hypertension and sleep apnea would be classified as Class II, Stage 2, and intervention would be recommended.

Sharma and Kushner also warn against using changes in BMI as a measure of success, noting, "Change in obesity class does not necessarily imply improvement or deterioration in overall health or well being. Conversely, relatively small changes in weight of only 5-10%, although associated with significant health benefits, may not be reflected by changes in obesity class."

Of course, most of us aren't able to use this staging system on a daily basis to measure our fitness goals, but it's a useful reminder of all the other aspects of health and weight loss beyond the number on the scale. Knowing all the ways that BMI breaks down when we apply it to ourselves is great start for changing how we think about weight loss goals. So, if you're feeling regret after stuffing yourself on holiday meals and thinking that 2015 is going to be the year that you lose 20 pounds or that you get your BMI down to under 25, considering picking a different metric for your fitness goals. Resolving to walk 10,000 paces a day, to spend more time playing outdoors with children, pets, or friends, or to find other ways to measure your health without weight loss as a proxy can be much more sustainable and rewarding than fighting a number. Happy New Year!


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