Is BMI beneficial for those who are serious about health? We’re breaking down the pros and cons of a weight measurement system that’s so simple it might be too simple.
Your body fat percentage isn’t the only indicator of your overall health, but it plays its role. It can be handy for women trying to manage their weight to get data and make well-informed decisions. That’s precisely what we’re taking you through today.
Here’s everything you need to know about body mass index (BMI), including how to calculate yours.
Oh, one quick note about sex and gender. Gender as a spectrum. In this article, we’re only using “female” and “male” to refer to the biological sex you’re assigned at birth.
Body mass index (BMI) is a formula used to measure body fat. Take your weight in kilograms and divide it by the square root of your height in meters. That’s your BMI score. You can also use the Centers for Disease Control and Prevention (CDC)’s online BMI calculator.
You’ve probably noticed that this formula doesn’t measure your body fat. What it does is compare your weight-vs-height to statistical averages. But according to the CDC, this is associated with more direct measures of body fat. In other words, most people can get an accurate picture of their health using BMI.
BMI uses the same scoring bands for all genders:
|18.5 or below||Underweight|
|18.5 to 24.9||Healthy weight|
|25 to 29.9||Overweight|
|30 and over||Obesity|
On average, BMI is a helpful way to explain health outcomes for most people. It’s quick, easy to understand, and used across the globe.
Using BMI, you can see whether you’re currently at a healthy weight. If not, you can adapt your lifestyle to gradually bring your score up or down to a sustainable level.
- kidney problems
- type 2 diabetes
- heart disease
- some cancers
BMI is simple, but it’s far from a perfect measurement of health. It’s geared towards averages, so it’s not as accurate for those with above-average heights – tall or short.
There’s a growing medical opinion that BMI is too simplistic. It can be particularly inaccurate when we account for:
- Body fat distribution
BMI and muscle mass
Muscle is more dense than fat, so one pound of fat will take up more space than one pound of muscle. Those with significant muscle definition and low body fat percentage might be considered overweight on the BMI scale.
Body fat distribution
People who are anatomically female have a different body fat distribution than those who are anatomically male. Women hold fat in different areas of the body than men.
BMI and age
Being overweight can have different outcomes as we get older. For postmenopausal women, an underweight BMI might be more serious than for someone who is younger.
BMI doesn’t account for ethnicity
As a health metric, BMI can’t account for genetic differences between ethnicities. Multiple efforts have been made to set different scoring bands for different ethnic groups, but these still aren’t perfect.
Decided BMI isn’t giving you the whole picture? There are other ways to measure body fat and get a snapshot of your health. Here are some alternatives.
Waist-to-hip ratio (WHR)
- Get a tape measure and a calculator
- Measure around your waist where it’s thinnest (usually around your belly button)
- Measure around your hips where they’re widest
- Divide your waist by your hips
The general idea is that your hips should be wider than your waist. A wider waist indicates more belly fat. For women, a WHR of .90 or lower is considered healthy.
Some limited evidence suggests WHR might be a more accurate predictor of health outcomes than BMI, especially in those who are elderly.
Now, this isn’t a perfect measurement of health either. It doesn’t account for height, age, or other criticisms we fired at BMI. While waist circumference alone can help track your fat loss journey, it’s less handy when comparing yourself with others.
If you want to get serious about your body fat, you might have to take a trip to the lab. A doctor can run different tests on you to get as accurate a picture as humanly possible. These might include:
- Skinfold measurements. Folds of skin are pinched and measured at different points around your body.
- Bioelectrical impedance (BIA). An electric current is passed through your body to estimate body fat percentage.
- Densitometry. Your weight is measured while you’re immersed in water and compared to your weight on dry land.
- Dual-energy X-ray absorptiometry. X-rays (which move through fat, muscle, and bone at different speeds) are used to calculate body fat percentage.
- Isotope dilution. You drink isotope-rich water and provide a sample of bodily fluids that tell doctors about your body’s performance.
Metrics like BMI give people the data to make informed choices about their well-being. But it could be a better system. Talk to a healthcare provider if you’re concerned with your body weight. They can run more useful tests to see where you’re at. They can also provide expert tips on how to enhance your health.