Why BMI Isn't The Be-All End-All Of Health
First of all, the 17th century creator of this formula was a mathematician rather than a physician, making his assignations as to whether a certain weight is healthy or not somewhat dubious. It's also a formula that he intended to be used to asses the fatness of entire populations rather than individuals.
Yet because BMI seemed to be a simple and seemingly scientific way to distinguish the skinny from the fat, it eventually became the gold standard for "diagnosing" someone as obese or overweight.
Unfortunately, using BMI to determine whether or not someone is overweight and to make important assumptions about their health could be disastrous for the not-insignificant percentage of the population for whom the measurement may be way off base.
First, the BMI formula assumes a high proportion of fat relative to muscle, so it can be wildly inaccurate for athletes and fitness buffs. Many super-muscular men would find themselves in the "obese" category when a body fat test or even a quick glance would show anyone that it wasn't the case.
BMI also doesn't account for the fact that women tend to have more body fat than men, or that even people of the same height may have quite different frame sizes and body shapes. Being "big-boned" is more than just a cliched excuse for those extra pounds; larger bones really will be heavier, so bigger boned people way be healthier at a higher weight than the truly petite.
For an idea of whether or not you're in that category, try wrapping your thumb and index finger around your wrist. If they overlap, you likely have a smaller frame; if they can't touch, you probably have a bigger one; and if they meet, you've probably about average.
Curvier women also need to take into account that they may have a good deal of fat in their breast and hip areas, which is less dangerous than abdominal or "visceral" fat, the kind which is most readily associated with ill-health effects.
The BMI formula also fails to account for possible differences in what an "unhealthy" weight is likely to be for people of different races. Asians tend to be metabolically "overweight," at a lower BMI than most Caucasians judging by body fat percentage and health markers, while the reverse is true for Polynesians and African Americans.
Such discrepancies may account for the fact that, when other measures are taken into account, more than 30 percent of people with "normal" BMIs were actually found to be metabolically unhealthy, while 15 percent of people who were even in the "very obese" category (BMI over 35) were healthy.
On a related note, nearly forty percent of people classified as merely "overweight" by BMI were actually "obese" when taking into account body fat, and about a quarter of those categorized as "obese" were not!BMI has also been shown to bear a different relationship to health in older populations, who may actually greater risk if their body weight drops too low than if they happen to be carrying a few extra pounds.
Even big-boned and athletic youngsters might be misidentified as "overweight" compared to other children their age and height, which could set the stage for lifelong image issues.
If being placed in a certain BMI category were only a matter of vanity, these discrepancies wouldn't be such a big deal. Yet these unreliable measures can have significant real world effects.
BMI can be used by insurance companies to determine premiums or as a factor determining admittance to eating disorder treatment programs, and it can certainly affect the health advice one might be given by their doctor, which could have ill effects on both smaller and larger folks.
If a doctor relies too heavily on BMI, they may "prescribe" weight loss to someone who doesn't actually need it, potentially leading them into a futile and painful cycle of yo-yo dieting when they were really at a healthy weight for them all along. They may also zone in on a person's unhealthy weight as the cause of any unusual symptoms and fail to diagnose other critical health issues.
Doctors may also fail to prescribe a healthier lifestyle to patients who don't present as obese or overweight according to their BMI but whose body fat percentage 0r unhealthy lifestyle puts them at significant health risk.A cleaner and healthier diet (that isn't necessarily a lower calorie diet) and regular exercise have also shown measurable benefits for plenty of physical and mental health conditions that have nothing to do with one's weight, but a doctor might not even think to mention it unless a patient is tipping the scales!
While waist circumference or waist circumference relative to hip circumference have been shown to be better indicators of health than BMI measurements are, these are harder to standardize, and methods that specifically measure body fat tend to be less available and more expensive.However, what you shouldn't do is take BMI's fallibility as a reason not to worry your weight at all rather than go out of the way to get yourself some better metrics. Though noone has the right to judge anyone on their body size, the health problems that can spring from an unhealthy weight and an unhealthy diet are very real indeed.You can, though, take your BMI categorization with a grain of salt. If you're eating healthy, moving often, and feel good and feel good about yourself, maybe your weight just isn't so big a deal, while if you're a not-so-heavy junk food junkie or couch potato, maybe it's time to give your lifestyle a second glance.