Parents, doctors, therapists, dietitians and patients: don’t even think about using BMI as a measure of “state!”
You have heard me say in my blog posts many times that, at Kartini clinic, we try to focus on “state,” not “weight.” That is, the state of good health as opposed to a given weight. As measures of this state of health, we use our metabolic labs, including measurements of thyroid health, sex hormones, leptin, glucose, insulin, cortisol and others. We also look at the return of menstrual cycles (related to those same labs), return of energy and normal socialization.
What we don’t look at is BMI, and here’s why:
Postulate a young girl who is 5 feet 7 inches tall and weighs 300 pounds. She would have a BMI of around 47: way off the chart for normal. Prior to the onset of her eating disorder symptoms, say, she eats heartily but normally –not markedly more than her peers, but every bite seems to stick to her. This metabolism runs in her family and many of her family members have type 2 diabetes and are very large but successful people. Nonetheless, she is quite active and loves to hike, although (because of her knees) she cannot hike as long or as far as some of her friends. She has low blood pressure and reasonable cholesterol. She is a straight A student, has the lead in the school musical for her singing talent and has never been in trouble.
Around age 16, our model girl gets the flu, is very ill and unable to eat for the better part of a week and loses about 10 pounds. At this point something seems to click in her brain and not eating feels good. She skips every meal except dinner after singing practice and has joined a gym. She has no time for her friends because she is now focused on weight loss. The next time we catch up with this young girl she weighs 210 pounds, 70% of her premorbid weight. And now her BMI is 33.
She goes to see her pediatrician and guess what the pediatrician says? “Good for you for losing all that weight! But your BMI is still in the obese range and you need to use your extraordinary willpower to lose a few more pounds — maybe another 40.”
This would be foolhardy advice indeed, as we are now talking about a “normal” BMI of 26, but a loss of nearly half of her body weight.
If the doctor took her nose up out of the BMI chart and looked at the patient, she would see a tired, pale young woman whose hair was lackluster and possibly falling out, whose tendon reflexes were slow and whose skin was doughy (low thyroid); such a patient would almost certainly be bradycardic (heart rate very low) and, with this catastrophic weight loss, probably orthostatic (blood pressure that drops dramatically when she stands up quickly) as well. She would need to be in the hospital.
If all you knew about such a patient was her BMI, you would think that she was healthy, and definitely “not too thin.” If you were were so misguided as to believe that only skinny people could have anorexia nervosa you would miss this diagnosis entirely.
I do not know how many times I have been told by a parent that their pediatrician dismissed their concerns about their child’s weight loss as “not a problem” because they were “still on the normal BMI chart.”
Cease this madness! BMI is not an accurate measure of a healthy state.