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BMI can oversimplify weight categories by ignoring natural fluctuations

BMI is a quick-and-dirty formula for categorizing individuals as "underweight," "healthyweight," "overweight," or "obese," based on height and weight - but it's far from perfect. Weight, like most elements of health, is a spectrum, not a series of boxes. Gaining or losing one pound could cause a person to skip between the "healthy" and "overweight" categories if BMI is the only measure taken into account. Not only does this mean that two equally healthy people whose weight differed by a single pound could be subject to very different treatment healthwise - it also ignores factors like daily height and weight fluctuations.

This morning, Obesity Panacea hosted a post by PhD student Ash Routen, whose recent research involved calculating schoolchildren's BMIs based on height and weight measurements taken throughout the day.

Routen measured 74 U.K. children's heights and weights in the morning, and then measured them again that same afternoon. He found that all the children were shorter in the afternoon, and that only the girls were heavier. Depending on the percentiles determining the various weight status categories (population-monitoring versus clinical cutoffs for the various categories), over the course of the morning either one or two girls has shifted from "healthyweight" to "overweight," and one moved from "overweight" to "obese."

These verbally drastic shifts in categorization resulted from minimal, natural fluctuations in height and weight. Routen concludes that studies of schoolchildren using BMI as a tool for determining health should be standardized, all taking place at the same time of day. I would add that actually observing people to see how healthy they look and taking factors like body fat versus muscle mass into account shouldn't be underestimated - especially when it comes to categories with such potentially harmful cultural and medical baggage.

Photo by cogdogblog

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