1. BMI is a weight-to-height ratio that’s used to categorize people by body mass.

It’s considered an indirect measure of body fat because it’s not actually a measure of how much fat is on your body. It’s an equation that has been found to get a number that is, moderately associated with more direct measures of body fat.

Healthcare professionals use BMI because direct measures of body fat, while more precise, are technically sophisticated and expensive. They are typically only available in labs and research settings. On the other hand, BMI takes just a quick calculation.

2. You get your BMI by dividing your weight in kilograms by your height in meters squared.

So, for someone who weights  68k) and is 6’ (or 1.82m) tall, the equation would look like this:

68 / 1.82*1.82 = 20.5

A BMI of 20.5 puts you in the “normal weight” range according to the BMI categories. You can check out BMI tables to see all the other ranges.

3. BMI’s most obvious limitation is that it can’t discriminate between body mass that comes from muscle and body mass that comes from fat.

For example: People with a good deal of muscle mass might have a BMI that puts them in the overweight range. When in reality their body fat percentage may not be high. On the other hand, elderly persons who are portly but have low muscle mass might have normal or even low BMI scores. This means BMI is underestimating body fat, not flagging a potential health risk that should be followed up on.

This is important because what doctors really care about when it comes to health is adiposity. Or how much of your mass is body fat, specifically how much you have and where you have it. The reason for this is that high percentages of body fat can be associated with cardiac risks.

4. A better way for you to get some potentially useful health-related info about body fat is to measure your waist circumference.

Having abdominal fat can be an indicator that you have visceral fat, or fat around your internal organs. This can increase your risk of diabetes, cardiovascular disease, and more.

To get your waist circumference, measure around the very top of your pelvis (on your bare skin) with a tape measure. A waist circumference of 35 or more for women and 40 or more for men is associated with increased health risks. This is a helpful, non-BMI way to gather some data about your abdominal fat.

5. If you’re happy and healthy, there’s no medical reason to lose weight.

Let’s say that by average or normative standards you weigh “too much” for your height. If you feel good, you’re happy, you’re leading an active lifestyle and eating a healthy diet, and your labs don’t show anything with respect to metabolic syndrome risks, there’s no reason to try to lose weight or lower your BMI.

The goal is a healthy lifestyle and reducing [your risk of disease]. we are happy as long as you are.