BMI stands for body mass index and is a way to determine if you’re weight is appropriate for your height. A high BMI is associated with increase risk for disease. It is the most often used tool in medicine to evaluate for overweight and obesity. It is useful for studying populations of people as a predictor of future disease risk, but has potential problems and pitfalls when applied to any given individual. Far from being an ideal tool BMI is simple to obtain and the main reason it is used most often.
How to Calculate BMI
BMI is simply calculated by taking you weight (either in pounds or kilograms) and dividing by your height squared (in inches or meters). When using inches and pounds the formula requires a conversion factor of 704.5. For instance, if you weigh 165 pounds and are 68 inches tall your BMI is 165 divided by (68 times 68) times a conversion factor of 704.5. When you do the calculation you get 25.14. There is no conversion factor if using the metric system.
If you are not good at math there are tables that can be used to determine your BMI.
The video below is helpful in understanding BMI.
How to Interpret BMI
- A BMI between 18.5 and 24.9 is considered normal.
- A BMI below 18.8 is considered underweight.
- A BMI of 25 to 29.9 is considered overweight
- A BMI of 30 to 34.9 is considered obese
- A BMI of 35 to 39.9 is considered severe obesity
- A BMI greater than 40 is considered morbid obesity.
To be considered a candidate for bariatric or weight loss surgery one must have a BMI greater than 40 without other disease, or a BMI between 35 and 39.9 in association of other disease like type 2 diabetes, high blood pressure, heart disease, and sleep apnea.
I Have a High BMI but Have Lots of Muscle
This is where BMI is not useful. Having a high BMI is unhealthy when the extra weight is in the form of fat as the real health concern is the portion of fat relative to body weight. Muscular athletes typically have high BMIs because of the addition muscle mass, but are not felt to be at higher risk of disease.
Body composition measurements are the best way to determine actual fatness, but require special testing. Another method to determine health risk related to body size is to measure waist size. This is done by placing a tape measure at the top of the iliac crest or top of hip bone and wrapping it around the abdomen parallel to the floor and measuring after exhaling. A waist size over 40 inches in men and 35 inches in women are considered to represent an increased health risk.
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