What is Body Mass Index (BMI)? Questions

Body mass index, or BMI, is a scale designed to measure body fat relative to height. According to the National Heart, Lung and Blood Institute (NHLBI), having a high BMI can increase your risk for heart disease and other serious health issues. However, BMI doesn’t take into account other factors about your body that are also important for determining your overall health. Keep reading to learn more about how BMI works and how it compares to other methods of measuring obesity.

What is body mass index (BMI)?

Body mass index (BMI) is a measure of body fat based on height and weight that applies to adult men and women. For most people, BMI is not a perfect measure of how healthy or fit they are, but it’s a useful tool for screening whether your weight could be putting you at risk of health problems.

For example, researchers have found that:

  • People with BMIs in the normal range (18.5-24.9) may still be at risk for health problems related to carrying too much weight if they have other risk factors such as high blood pressure or high cholesterol levels.
  • Adults who have a BMI between 25 and 29 have an increased risk for heart disease and type 2 diabetes compared to adults with lower BMIs; this increased risk increases as their BMI rises into the obese range (30-39). This means that adults who are overweight should take action now so they can lower their health risks before they become obese.

Is BMI the best way to measure obesity?

BMI is a good measure of obesity, but it’s not perfect. For example, BMI doesn’t take into account what your body fat percentage is and only takes into account height and weight. It also doesn’t take into account how much muscle mass you have or any other health factors that might affect your health.

If I have a high BMi, does it mean I’m overweight or obese?

The answer to this question is no. BMI is not a measure of fatness; it’s just a ratio between height and weight. BMI may be useful as one indicator of body fatness, but it can’t take into account other factors that can influence your health, such as how the fat you carry is distributed, how much muscle you have, and even your age.

Another important point: Body mass index doesn’t tell you anything about what kind of weight gain or loss might be best for your health. For example, if someone gains 20 pounds by adding muscle instead of fat (something we call “lean mass”), their BMI won’t change at all!

So if you’re worried about being “overweight,” don’t focus on something like BMI—your doctor will help figure out the best way for you to lose weight and keep it off so that it improves both your heart health AND overall well-being.

Does having a high BMI mean I have heart disease?

Having a high BMI is associated with an increased risk of developing heart disease and stroke, but it’s not the only thing that contributes to these conditions. Other factors include smoking, high blood pressure and diabetes.

It’s important to remember that just because you have a high BMI doesn’t mean you will develop heart disease or stroke. Having a healthy diet and lifestyle can help lower your chances of getting these conditions.

Does BMI consider where we carry body fat?

BMI does not take into account the amount of body fat that you have. In fact, it doesn’t distinguish between muscle and fat at all. BMI is based on your height and weight, so if you have more muscle mass than someone else with a lower BMI, you can have a higher score.

Additionally, BMI doesn’t consider body shape or bone density (which can affect how your body stores fat). For example:

  • Someone who has an hourglass figure—wide hips, narrow waist—may have trouble losing weight because they carry their pounds around the middle of their bodies instead of in their arms or legs; this person might be considered obese even though there isn’t much fat on them.
  • A person who’s very tall with little lean muscle may end up with a high BMI simply because they weigh more than someone shorter but with more lean mass.

If my BMI is low, does that mean I am at a healthy weight?

Adding a few pounds to your frame might not be the worst thing in the world, but it does have its downsides. Excess body fat is associated with a number of serious health issues including heart disease, type 2 diabetes and cancer. Here are some things to consider when calculating your BMI:

  • If your weight falls on the low end of normal range (less than 18.5), this can be a sign of an eating disorder or malnutrition. Talk to a doctor if you think you may need help getting healthy again.
  • If you fall into the overweight category (between 25 and 29), it’s important that you start taking steps toward losing weight through dieting and exercise so that your risk for these diseases is reduced over time.
  • If your BMI indicates obesity (30 or higher), then it’s especially important that you take steps toward losing weight immediately since obesity has been linked with increased mortality rates overall among adults in most countries around the world.”

What is an underweight BMI?

An individual with a BMI of less than 18.5 is considered to be underweight, while someone at the other end of the spectrum with a BMI of 40 or more is considered morbidly obese. If your BMI falls between 18.5 and 24.9, you are considered to be in the normal range—that’s good news!

A person whose body fat is within the normal range faces no risk of obesity-related diseases such as type 2 diabetes and hypertension (high blood pressure).

The Centers for Disease Control and Prevention (CDC) defines weight status using ranges that differ slightly from those used by researchers and health professionals:

  • Underweight: Less than 18.5
  • Healthy weight: 18.5–24.9
  • Overweight: 25–29.9
  • Obese I: 30–34.9
  • Obese II: 35–39.9
  • Obese III/severe obesity: 40 or greater

Having a high BMI doesn’t automatically mean you’ll have heart problems or other health issues.

Although having a high BMI is associated with an increased risk of health problems, it doesn’t automatically mean you’ll have them. For example, if your weight is mostly due to muscle mass and not fat, your health may be fine.

Muscle weighs more than fat, so a person can be overweight or obese but still appear fit. That’s because the body mass index (BMI) doesn’t take into account muscle mass and what percentage of your body weight comes from fat versus muscle tissue. Additionally, some people lose weight in their thighs and hips while maintaining their chest size as they age — which would increase their BMI without reflecting any real change in their health status!


That being said, if you’re worried about your weight or if you have any questions about your health, it’s always best to talk with a medical professional. There are also a variety of online tools that can help you calculate your BMI. And remember, BMI is not the only way to measure obesity.