BMI – What is it and why is it important?

bmiWhen you have an appointment at the clinic, a health-care provider often takes your vital signs. Vital signs generally refers to measurement of your body temperature, blood pressure, heart rate, weight and height. From the weight and height, your BMI can be calculated.

What is BMI and why does your physician monitor it?

Catherine McNeal, MD, PhD, Internist, Pediatrician and specialist in lipid disorders, explains BMI and discusses why it’s important.

Every little bit you can lower your BMI is a step toward improving your health and lowering your risk of developing the diseases associated with obesity.

BMI is your body mass index, which is your weight in kilograms (kg) divided by your height in meters squared (m2).

“The BMI is a way to adjust your weight for your height. A short person will have a lower weight than a tall person, but he may have the same BMI,” explains Dr. McNeal.

BMI is a measure used by the medical community to define normal and abnormal weight adjusted for height. The definitions are:

  • Underweight: Below 18.5 kg/m2
  • Normal: 18.5 – 24.9 kg/m2
  • Overweight: 25.0 – 29.9 kg/m2
  • Obese: 30.0 – 39.9 kg/m2
  • Morbidly obese: 40.0+ kg/m2

Calculate your BMI here


According to the Centers of Disease Control, of U.S. adults:

  • More than two-thirds are overweight
  • More than one-third are obese
  • 4.7 percent are morbidly obese

Normal and abnormal BMI values, Dr. McNeal says, are defined differently in children because they are growing and because BMI is different in boys and girls. Consequently, normal and abnormal values in children are based on percentile values — that is, how they compare with other children their age and gender. Please see our blog on BMI in children.

BMI as a Predictor of Health Risk

The higher your BMI is the greater the risk is that you might develop other health-related problems.

A BMI higher than 25 kg/m2 can increase the likelihood that you may develop a number of problems, including type 2 diabetes mellitus, high blood pressure and an abnormal amount of fat in the blood. Each of these “risk factors” can increase the chance of developing cardiovascular disease (heart problems and stroke, for example) and/or other serious health issues, says Dr. McNeal.

Tracking BMI is a way of monitoring your risk quickly and easily.

A BMI in excess of 25 kg/m2, according to the CDC, can put you at greater risk of:

  • Heart disease
  • High blood pressure
  • Problems with blood sugar ranging from an impaired fasting blood sugar (i.e., a fasting blood sugar above 100 mg/dL but below 126 mg/dL) to type 2 diabetes mellitus (a fasting blood sugar above 126 mg/dL on at least two separate occasions)
  • Low HDL cholesterol and high triglycerides
  • Stroke
  • Osteoarthritis
  • Early degenerative arthritis – from the increased weight stress on bones over time
  • Polycystic ovarian disease
  • Sleep apnea
  • Certain cancers, such as breast and colon
  • Infertility
  • Difficulty with pregnancy

What to Do?

Every little bit you can lower your BMI, Dr. McNeal says, is a step toward improving your health and lowering your risk of developing the diseases associated with obesity.

“Not getting overweight in the first place is probably the easiest way. But if you are overweight,” Dr. McNeal says, “at least trying to make sure you don’t continue to gain extra weight is the next best thing. Optimally and probably over an extended time gradual weight loss to reach a normal BMI will help to ensure better health as a person ages.”

Dr. McNeal’s advice: “Find some small thing that you can change and start there. For example, a 30-minute walk at a normal walking pace probably burns off only the amount of calories in a slice of bread — about 100 calories. Although this is only equal to about 1/35th of a pound, done consistently over time, this change can add up to a measurable loss in weight. Consistent exercise can also help to prevent loss of muscle mass or may even gradually increase muscle mass (depending on the type of activity), which well help to lose weight.”

Dr. McNeal suggests beginning with a slightly smaller portion sizes, eating fruit instead of drinking juice, reducing or eliminating other sugared beverages, and eating out less frequently or sharing an order when you do eat out.

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BMI – What is it and why is it important?