It’s Time We Stop Using BMI as a Measure of Health

Body Mass Index or BMI can be just one more lens through which we judge our bodies.  With eating disorders one often feels that they must be at the very low end, or better yet, below the healthy range. But what is a healthy range really? Recent research shows that by a certain age, mortality rates (the number of deaths in a given area or period, or from a particular cause) are actually lowest in the overweight category. A mathematician, not a physician, created BMI over two hundred years ago.  It doesn’t take gender, muscle mass or bone density into account. Therefore, as we all know by now, a fit, muscular, strong-boned person can easily fall into the overweight or even obese category.  

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Another interesting fact is that in 1998 the BMI ranges were actually lowered by the World Health Organization (WHO). Overweight BMI, which used to be 28 for men and 27 for women, was now 25 for both genders. BMI also does not tell us anything about the percentage of which type of fat our bodies possess.  Visceral versus subcutaneous fat for example, has different impacts on health. One’s ethnicity which may play a role in muscle and bone density, can further call into question the use of the same BMI ranges for every continent.

Something I find particularly disturbing is that schools across the country continue to calculate the BMI of their students and even send home letters placing them in categories of acceptability. A child’s growth should be a matter between the parents and pediatrician, not the school. This creates confusion, shame, and at times “special” physical education classes for those students who are in the overweight category. Imagine the shame this causes children. I have had clients end up in my office with eating disorder behaviors simply due to this practice.  BMI is not a good measure of health for children, especially for those that are younger. A full assessment of each child’s individual growth curve seems to make more sense. A child that has always rested above the 85th percentile for weight for example, should not be encouraged to reach the 50th percentile. The weight itself tells us little about the child’s skeletomuscular density. I have also had children end up in my office after they were counseled by their pediatricians to lose weight when their growth pattern was completely normal but above that 85th percentile. It shouldn’t come as a surprise that these clients ultimately received Anorexia Nervosa Diagnoses.  Fortunately, in 2016 the American Academy of Pediatrics released new guidelines for the prevention of obesity and eating disorders which, include discouraging dieting and focusing on healthy living and healthy habits rather than weight.

For an interesting documentary on schools and BMI visit https://www.thestudentbodyfilm.com 

Despite major pitfalls, BMI continues to be used as a measure of health, as does ideal body weight (IBW), which is yet another frustrating topic. I appreciate that Marcia Herrin, Ed.D., M.P.H., and Maria Larkin, MEd, RDN, LD, authors of Nutrition Counseling in the Treatment of Eating Disorders coined the term biologically appropriate weight or BAW. According to Herrin, “Biologically appropriate weights are weights that are easily maintained without the practice of dieting or other inappropriate food and exercise behaviors. A BAW reflects pre-morbid weight, normal physical and psychological function, genetic predisposition (ethnicity), gender and family history. In children and adolescents, a BAW supports normal growth and development and considerable improvement in an eating disordered patient's obsessions and preoccupations with food, shape, and weight. BAW in older patients is also associated with improvement in attitudes about food, shape, and weight. In older females, BAW are stable weights at which normal menstruation and ovulation are maintained and for males this is also a stable weight at which normal testosterone levels are restored.” 

 Read Herrin’s blog on What is Biologically Appropriate Weight

There are Better Parameters of Health 

To measure complete health we have to take into considerations such things as functional ability, psychological well-being, social networks, and quality of life. Besides diet and physical activity, we have to include alcohol consumption, smoking, drugs, and sexual lifestyle. But for those of you who like numbers, here are some that, until further research, seem more valid than BMI. 

Blood pressure It is still good for your heart to keep BP below 130/90. However lower is not always better. We want those numbers above 90/60 as well. And if orthostatic vitals are performed we want that blood pressure to remain relatively stable without large increases or decreases. Blood pressure drops from lying to standing greater than 20 systolic points or 10 diastolic points can indicated instability. 

Heart Rate Yes a lower pulse at rest typically means a more efficient heart. However if intake has been suboptimal, a heart rate below 60 bpm or what is called bradycardia can result. Tachycardia or a heart rate above 100 bpm isn’t ideal either; it can indicate something as simple as over-caffeination or as serious as abnormal thyroid activity. A healthy pulse falls somewhere between 60-100 beats per minute.

In terms of pulse another measure of health or fitness is how quickly that pulse can return to baseline after we are exposed to stress or exercise.

Serum lipid levels For now total cholesterol, LDL, HDL and TG remain markers of health. There continues to be much research on this topic including on Apo lipoproteins.  I will only speak of what I am currently aware of.

Total cholesterol should be below 200 mg/dL

HDL should be above 50 mg/dL for women and above 40 mg/dL for men 

LDL should be below 100 mg/dL for both women and men. 

Triglycerides (TG) should be below 150 mg/dL for both women and men.

For now by aiming for heart healthy fats on a daily basis and fatty fish twice per week along with more whole, plant foods and moderate exercise remains protective for the heart. 

Blood Glucose levels. Both low (hypoglycemia) and high (hyperglycemia) glucose levels in our blood are problematic. We more often focus on the high end of this equation due to the large numbers of people diagnosed with type 2 Diabetes. However when blood glucose drops below 70 mg/dL, fasting symptoms such as light-headedness, heart palpitations, and shakiness develop. Over time this affects ability to concentrate and focus. Eating a balance of nutrients including consistent complex carbohydrates throughout the day remains effective in fighting both hypo and hyperglycemia

Fasting Insulin Levels measures how well your body secretes and uses insulin. We want fasting insulin to remain below 25 mIU/L

Where do we go from here?

I imagine BMI will continue to be used as a measure of health for some time. I would like to say that I will stop using BMI in my clinical practice, but with clients’ insurance coverage for much needed treatment still riding on these numbers I cannot leave them out completely. What I can do however is continue to advocate for the proper medical care for each person based on all symptoms. I will take seriously when a child deviates from their own particular growth curve, regardless of their percentile. I will highlight all the ways in which someone struggles that has nothing to do with BMI. I will not invalidate anyone based on their weight.

I look forward to a time when less people fall for the fallacy that our health is contingent on being thin. Better yet, I look forward to a future when no person correlates their self worth with attaining a particular weight.