What Your BMI Might – and Might Not

The body mass index (BMI) has long been used as the gold standard to indicate high body fatness. But your BMI may fall short at telling the whole story when it comes to your health.

As we become more health aware as a society, many of us already have a pulse on what our basic health numbers like blood pressure and cholesterol mean. But how well do you know your BMI? The BMI, or body mass index, measures how healthy your weight is in relation to your height and offers your provider a guess as to what your risk may be for weight-related issues down the road. While your BMI may not necessarily reveal the whole picture, understanding it is important because any change to it has the potential to affect your health for the better or for the worse.

How is your BMI calculated?

To calculate your BMI, all you need is your weight and your height. BMI calculators are available online to quickly crunch the numbers for you, or you can try your hand at plugging your numbers into this formula:

The BMI number you get lets you know where you fall within the following weight categories:

Below 18.5 – underweight

Between 18.5 and 24.9 – healthy weight

Between 25 and 29.9 – overweight

30 and higher – obese

What a high BMI could mean for your health

Paying attention to your BMI is important because a high BMI means you are at elevated risk for a number of serious health problems, and the higher the BMI, the more elevated your risk. For example, people who are overweight or obese are much more likely to have the tell-tale markers of heart disease like hypertension and high cholesterol and are also at higher risk of cancers of the uterus, gallbladder, kidney, and cervix. A rise in BMI often comes with a rise in insulin resistance as well, a warning sign that diabetes may not be far behind.

How reliable is the BMI as a health indicator?

A high BMI can be concerning to be sure, but just like any health measure, the BMI has limitations and is not a true indicator of health on its own. For one thing, the BMI does not differentiate between fat and lean mass, or the muscles and bones in your body, so it does a poor job of predicting how much fat versus muscles you actually have. Muscle is denser than fat, so very muscular people like athletes may have BMIs that classify them as obese even though they have a low percentage of body fat. Secondly, BMI does not say if the kind of fat you do carry is visceral fat, the alarming kind of fat that is stored around your waist and can envelop vital organs, heightening the risk for heart disease even more.

I just learned I have a high BMI – now what?

If you fall within the overweight or obese category, your provider may also want to measure around your waist to get an even clearer picture of your health risks. If your waist size is bigger than 35 inches as a female or 40 inches as a male, and most of your fat is around your middle instead of your hips, your risk for heart disease and diabetes rises. But the encouraging news is that there is something you can do about it. Even if you do have a high BMI and waist size today, just a small drop in weight, even as little as 5 to 10 percent, can lower your risk for many obesity-related conditions.

The bottom line about your BMI

Your BMI is just one of many tools your healthcare provider uses to gain insight about your health, and on its own, it cannot indicate how healthy you really are. Your BMI need not define you. But like any health marker we rely on, a BMI out of the normal range can help warn us of potential trouble down the road and should not be ignored. The great news is that your BMI is not set in stone. It can change for the better – and your risk for disease can lower - the more weight you lose. So, adopting a long-term healthy lifestyle with lots of physical activity, nutritious eating, and portion control will help to trim your waistline and keep you thriving for years to come.