What Does Your BMI Really Tell You?
By Jeanne Hendricks, Manager, Virtua Nutrition and Weight Management
Body-mass index (BMI) calculators can be a helpful tool to indicate your risk for disease, but they don’t tell the whole story. They just offer a starting point to look at overall health.
What is BMI?
BMI is a number that measures weight in relation to height. You can use a BMI calculator, or calculate it yourself by dividing your weight (in pounds) by your height (in inches) squared and multiplying by 703. Here’s an example if your weight is 150 pounds and height is 5'5" or 65”.
- Calculation: [150 ÷ (65)2] x 703 = 24.96
The results are classified on the following scale:
- 18.5 or under: underweight
- 18.5-24.9: average
- 25-29.9: overweight
- 30 or over: indicates obesity
What does BMI tell you?
A high BMI may indicate that you’re at risk of developing health conditions like cardiovascular disease, type 2 diabetes, hypertension or high cholesterol. However, it’s important to keep in mind that BMI only measures weight in relation to height.
What doesn't BMI tell you?
BMI doesn’t directly measure body fat or account for different variables that may affect weight and health.
For example, two people with the same BMI might have completely different body types and health conditions. To accurately assess your risks for health conditions associated with a high BMI, you also must consider family history, personal medical history, and other individual factors like muscle mass or bone density.
What affects BMI?
Muscle mass and bone density can result in a high BMI for people who aren’t overweight.
If someone is active—even if they're not an athlete—their muscle mass is going to be a bit higher. Since muscle increases weight, it could technically put them in an overweight category in BMI parameters.
Bone structure has a similar effect. People with larger frames are likely to have higher BMIs, but that doesn’t automatically mean they are at higher risk for disease.
Alternatives to BMI
There are other measurements that more accurately indicate if your weight can affect your health, but they are more difficult to measure.
Waist-to-Hip Circumference: This measurement compares waist circumference to hip circumference. If waist and hip circumference are close to each other, it may indicate that body fat is being stored in the abdomen around the organs. This puts people at higher risk for cardiovascular disease, type 2 diabetes, hypertension and high cholesterol.
Body Fat Measurement: This metric uses an instrument called calipers to pinch the skin and measure body fat.
Both waist-to-hip circumference and body fat measurement should be done by healthcare professionals who know how to do the measurements correctly to produce accurate results.
Hendricks stressed that BMI is useful because it’s an equation anyone can do if they know their height and weight. It’s a quick indicator to understand if you could be at risk for weight-related diseases.
However, she encourages people not to just focus on that number. Focusing on overall health is most important. If you can focus on that, the weight will fall to where it needs to be.
Updated February 15, 2017