Myth of the Day: BMI is the Bible
It’s Halloween. If you’re anything like me, you’ll wake up tomorrow with a candy corn hangover and bear down for the upcoming firehose of holiday temptations.
Don’t get me wrong: I love the holiday season. Pumpkin pie and candy canes make life worth living. But for many of us, the next two months will be open season for self-sabotage and guilt.
But instead of depriving ourselves of pleasure and plum pudding, let’s simply pause and pace ourselves. Let’s anticipate the remorse many of us will feel in the New Year, and decide right now to be more intentional about how we feed our bodies — and how we talk to ourselves about weight.
The next three weeks of this newsletter will be a myth-busting series on diet, exercise, and weight loss.
These are tricky subjects. There is no one-size-fits-all recommendation on healthy eating and weight. But literally hundreds of you responded to my recent poll, asking me to write more about weight loss. So here we go.
One of you wrote me this:
Hi Dr. McBride, Is BMI an accurate depiction of health? I recently had a doctor tell me I was "borderline obese" based on my BMI, despite being incredibly active and healthy, strength training 3+ times a week, doing cardio 5-7 times a week, and eating a diet mostly consisting of unprocessed fruits, veggies, etc., I have an amazingly low cholesterol and LDL levels, and lots of muscle... I was shocked and hurt that she said this (not to mention her lack of collecting any data on past eating disorders, mental health state, diet, exercise, etc)
This woman’s story highlights many common misconceptions about weight — from patients and doctors alike — and helps frame today’s post.
Myth #1: BMI is the bible
Body mass index (“BMI”) is defined as our weight in kilograms divided by the square of our height in meters. The BMI categories are:
Underweight = <18.5
Normal weight = 18.5–24.9
Overweight = 25–29.9
Obesity = BMI of 30 or greater
BMI is kind of like the SAT: it gives us one data point, but says nothing about our overall worth or ability to thrive in the world. BMI maps height and weight, but tells us nothing about body composition (muscle versus fat), metabolism, and overall health. Physicians who rely solely on BMI to recommend weight loss deprive patients a more nuanced conception of their health. Patients who anchor their health outlook and goals to this number potentially do themselves harm.
What matters more than BMI is context.
For people living with overweight or obesity, how is your cholesterol and blood sugar? Do you have a family or personal history of metabolic problems like insulin resistance, thyroid disturbance, or PCOS? What is your appetite like? Does your exercise routine include strength work? How are your knees and hips? Do you snore? Do you stress-eat or restrict? Or do you look at your “thin” friends who eat more than you do and wonder what the hell is going on with your body? What are your (and not necessarily your doctor’s) health goals — to lose weight, to get stronger, or perhaps to feel more in control of your health without losing a pound?
In other words, the key is for doctors to focus on the genetic, hormonal, behavioral, nutritional, and psychological context around weight and BMI — and for patients to gain the tools, information and agency to change when it’s needed, possible, and desired for them.
While the potential health effects of overweight and obesity are real and important, sometimes people with a higher-than-ideal BMI don’t need to change anything at all.
Take the newsletter reader above. She is a perfect example of someone whose BMI is technically “too high,” but whose cholesterol, nutritional inputs, and exercise routine are excellent. If I were her doctor, I would not counsel her to lose weight if 1) she doesn’t have any medical or psychological reasons to lose weight and 2) her nutritional and exercise habits are sustainable and satisfying.
Instead, I would reinforce the positive impacts of healthy eating and regular exercise on her overall health. I would counsel her on the potential risks of extra weight balanced with the downsides of altering her already-great lifestyle choices. I would continue to check in with her on her habits and goals.
On the flip side, I have many patients whose BMI is “normal” but whose calories come largely from processed food, sugar, and alcohol; whose high cholesterol is rooted in lifestyle more than genetics; and whose body fat percentage is higher than ideal. I don’t tell these patients that they’re “healthy” just because they have a normal BMI — nor do I shame them for their habits. Instead, we delve into the psychological, genetic, and biological roots of their behaviors, assess their health ambitions, and come up with a reasonable and sustainable way to affect change over time.
We are more than our BMI.
As we ponder the next few months, let’s replace shame with realistic goal-setting. Let’s focus on healthy habits rather than the number on the scale. Let’s remind ourselves how good we feel — mentally and physically — when we make healthy choices and save room for pumpkin pie.
Tune in next week for part two of myth-busting about weight and weight loss.
Meanwhile, check out this week’s podcast episode!
This week, we go Beyond the Prescription with award-winning journalist, producer, and documentarian Soledad O'Brien. She discusses her new film, The Rebellious Life of Mrs. Rosa Parks, the first-ever full documentary of one of the most celebrated — and misrepresented — Americans of the 20th century. We discuss the importance of storytelling to accurately portray historical figures; to lift up marginalized populations; and to educate us all. Soledad talks openly about the personal and professional challenges she has faced as a woman of color and her “life hacks” for taking care of her physical and mental health.
As always, my newsletter subscribers get early access to the pod every Monday night before the official Tuesday launch. Give it a listen now on Apple, Spotify, or wherever you find podcasts. And I’d be thrilled if you could rate and review the show. It helps me a ton!
I will see you next week. Until then, be well.