BMI — body mass index — comes up in almost every intake conversation I have. It's something clients mention frequently when they describe why they decided to seek nutrition support.
"My doctor said my BMI is too high."
I understand why it gets so much attention. BMI is fast, accessible, and gives a quick reference point. But as a measure of individual health, it has significant limitations that are worth understanding — especially if you've been told your BMI is a problem.
What BMI Actually Measures
BMI is a ratio of weight to height, calculated by dividing weight in kilograms by height in meters squared. That's it. It was originally developed in the 1800s as a statistical tool for population studies — not as a clinical measure for individual health assessment.
It does not measure body fat percentage. It does not distinguish between muscle mass and fat mass. It does not account for where fat is distributed in the body, which matters enormously for metabolic health. It does not factor in age, sex, ethnicity, fitness level, or any of the individual variables that actually predict health outcomes.
What BMI Gets Right
At the population level, BMI correlates with certain health risks. Very high BMI is associated with increased risk of cardiovascular disease, Type 2 diabetes, and joint problems. Very low BMI is associated with increased risk of nutrient deficiency, bone density loss, and immune dysfunction.
As a rough screening tool, it can flag individuals who might benefit from further assessment. That's a legitimate use.
What BMI Gets Wrong — Consistently
It misclassifies a significant number of people. Highly muscular individuals — athletes, people who strength train regularly — often fall into "overweight" or "obese" categories despite having very low body fat and excellent metabolic health markers. Meanwhile, individuals with "normal" BMI can have high visceral fat and poor metabolic health.
Research has also consistently shown that BMI thresholds were developed based primarily on white European populations and perform differently across ethnicities.
A number that doesn't account for who you are, how you're built, or how you actually feel is a very limited measure of your health.
What I Use Instead
In my practice, I look at the full picture: blood work (glucose, A1C, lipid panel, inflammation markers), blood pressure, energy levels, sleep quality, digestion, strength and mobility, and how someone feels day to day. These are the measures that actually tell us how someone's body is functioning.
I also use waist circumference and waist-to-height ratio, which are better predictors of metabolic health than BMI because they reflect visceral fat distribution specifically.
BMI is one data point among many. In our work together, we look at the full picture.
Health is more than a number. Let's look at the full picture together.
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