BMI and Your Health: How Are They Connected?

Among all the numbers your healthcare provider records at your appointment — blood pressure, cholesterol, body temperature, etc. — your body mass index, or BMI, is the one that may be most likely to stick in your memory. BMI is a number based on your height and weight, which helps your provider determine whether you have obesity, overweight, within a normal range, or underweight.

BMI can be a sensitive topic, and it has its critics. “Unfortunately, there is no perfect tool [to measure one’s health],” says Anisha Abraham, MD, interim chief of the division of adolescent and young adult medicine at Children’s National Hospital in Silver Spring, Maryland. Instead, it is one of several measurement tools, including blood pressure, blood sugar, and others, that tell us different things and are pieces of a larger puzzle, she says.

Body fat percentage is another one. Frank Contacessa, MD, an internist in Armonk, New York, says that it’s a better factor to consider in a holistic health assessment. Still, it’s more challenging to measure than BMI.

Here’s an overview of how and why BMI is used, and what yours may mean.

BMI is a common measurement when considering a person’s future potential health issues because it’s quick, easy to calculate, and free, says Linda Anegawa, MD, a Honolulu-based board-certified physician in internal medicine and obesity medicine.

When measuring health risks across a population, BMI can be advantageous, especially because it’s more widely used than other weight measurement approaches, says William Yancy, MD, a professor of medicine at the Duke University School of Medicine in Durham, North Carolina.

To calculate your BMI, take your weight in kilograms and divide it by your height in meters squared. Alternatively, take your height in inches squared, divide that by your weight in pounds, then multiply by 703.

Here is the BMI range, and how the CDC describes each:

• Below 18.5 is underweight (too low)
• 18.5 to 24.9 is normal weight (just right)
• 25 to 29.9 is overweight (high)
• 30 or higher indicates obesity (very high)

There are two sides to this argument. On one hand, many public health experts say that knowing your BMI is good information to have — and that if your BMI is considered too high or too low, getting it back into a healthy range can potentially reduce your medical costs and possible risk of future health problems.

On the other hand, some healthcare professionals choose not to emphasize BMI. “I do not focus on a patient’s BMI when I counsel them on being healthy,” Dr. Contacessa says. “There is no single indicator of total health. You have to look at the totality of a person, including a family history, lifestyle review, and physical exam.”

The flaws of using BMI as a measure of health are well documented.

“If BMI is the only thing your doctor uses, you should also use other measurements,” says Yancy, who advocates for knowing your waist circumference. “That’s actually a better predictor of your health, as carrying fat around your midsection is riskier than other parts of your body.”

The more fat you have around your middle (visceral fat), the more your health may take a hit, regardless of BMI, echoes Patrick M. O’Neil, PhD, director of the weight management center and a professor in the department of psychiatry and behavioral sciences at the Medical University of South Carolina in Charleston.

These details about what makes up your body weight and where on the body it’s distributed matter and are needed to determine potential health risks. “One could have a higher BMI and yet be free of health conditions,” Anegawa says. “On the other hand, some individuals with lower BMIs have very significant weight-related diseases, such as prediabetes and type 2 diabetes, hypertension, or abnormal cholesterol.”

Put differently, when it comes to BMI and your actual risk of health issues, it’s complicated.

Something to keep in mind is that a focus on BMI in the doctor’s office or your daily life may increase weight stigma and harm your mental health. “Overfocusing on BMI can affect self-esteem and emotional wellness,” Dr. Abraham says. “For example, I have had patients who developed body image and eating disorders as a result of being told that they had a high BMI and needed to change their weight.”

High Blood Pressure A higher BMI is linked to higher blood pressure readings.

Being underweight may also leave you with lower energy reserves if you do become ill. “People who are acutely ill have better survival or outcomes if they had a bit of fat storage to begin with. Those who are overweight seem to do best in these situations,” says Yancy.

• A BMI range that says you’re overweight or have obesity doesn’t necessarily mean you are unhealthy.
• Healthy eating and exercising habits may mean more than what the scale or BMI calculator says.
• Some research shows that being overweight may be protective of your health. In younger adult men, according to one study, being overweight was associated with a lower risk of death from any cause. The same was true of middle-aged women.

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• Rather than aiming for a specific BMI number, what may be most important is maintaining — or starting — healthy habits.