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Is BMI an important factor in measuring overall health?

Body Mass Index (BMI) is the most common way to classify obesity in adults. However, BMI is often discounted as an inaccurate measure of an individual’s health. While there are special circumstances in which BMI may not be the most accurate indicator of obesity, a vast majority of the time BMI is an important and valuable measurement that provides insight into a person’s risk for disease.

What is BMI? How is BMI measured?

BMI is a calculated value used to measure obesity. While BMI does not directly measure an individual’s body-fat percentage, there is a strong correlation between BMI and body composition.  To accurately calculate BMI, a person’s weight (in pounds) should be divided by his/her height (in inches) squared, and then multiplied by the conversion factor of 703.1 For adults, BMI values are as follows:2

  • BMI <18.5 is considered underweight
  • BMI between 18.5-24.9 is considered normal/healthy
  • BMI between 25-29.9 is considered overweight
  • BMI >30 is considered obese 

Why is BMI considered not reliable? Does BMI account for muscle?

People often say that BMI is not an accurate depiction of health since it does not take increased muscularity or the location of body fat into account. While it is true that BMI values do not account for muscle mass, this would only impact highly conditioned athletes.3 Additionally, body fat in the waist and chest (abdominal adiposity) is thought to be more dangerous than weight that accumulates in other areas. However, BMI is still important because it predicts disease risk accurately and effectively, regardless of the location of body fat (for anyone who is not a highly conditioned athlete).4

What else does BMI not take into account?

Individuals often state that BMI is not a reliable measure. While that is not true, there are factors that BMI does not take into account, including:6

  • Muscle mass
  • Bone density
  • Body fat percentage
  • Your age
  • Your activity level

All of these factors, as well as data from blood work, also contribute to overall health.

Is BMI useful? Yes!

The importance of BMI steps from its role in identifying potential risk of disease. BMI has a longstanding history as the go-to measure for obesity, and as such, years of research have proven that BMI provides insight into health risks associated with being overweight or obese. High BMI values strongly correlate to an increased risk of coronary heart disease, type 2 diabetes, and hypertension. Since these diseases develop over time, a high BMI can serve as an early warning sign that someone is at risk. Additionally, a high BMI has also been associated with sleep apnea and gallbladder disease, along with increased body and joint pain.5

Is BMI a good indicator of health?

BMI alone is an accurate health indicator, but the value is even more useful when examined in conjunction with other measurements, such as metabolic syndrome values. Assessing other values along with BMI provides an overall picture of a person’s health, and may highlight early signs of disease risks even if the individual falls into a healthy BMI range.

What are other similar methods to accurately measure health?

For adults, measuring both BMI and waist circumference likely provides the most value in predicting weight-related disease risk, and helps alleviate concerns that BMI alone is not a reliable measure.7

  • To accurately measure waist circumference, individuals:
  • Hold a tape measure on the abdomen just above the hip bone
  • Ensure the tape measure is snug around outer layers of clothing
  • Keep the tape measure parallel to the floor (make sure it is not twisted)
  • Wrap the tape measure around the waist

Waist circumference is also a key factor in metabolic syndrome as it indicates central obesity. If the waist measurement is more than 40 inches for men and more than 35 inches for women, the individual is considered to have central obesity.

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Sources:

1, 2, 3, 5, “About Adult BMI.” Centers for Disease Control and Prevention. 2015. http://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html.

4, “Why Use BMI.” Harvard School of Public Healthhttps://www.hsph.harvard.edu/obesity-prevention-source/obesity-definition/obesity-definition-full-story/#references.

6, “What your BMI doesn’t tell you.” WebMDhttps://www.webmd.com/diet/features/bmi-drawbacks-and-other-measurements#3

7, “Why use BMI?” Harvard Obesity Prevention Sourcehttps://www.hsph.harvard.edu/obesity-prevention-source/obesity-definition/obesity-definition-full-story/ 

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