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Healthcare providers often look at patients’ body mass index (BMI) as an indicator of health and potential risks. We’re told that “normal” BMI is between 18.5 and 25, and anything outside this range is classified as underweight, overweight, or obese. However, these measurements are broad generalizations that were meant to reflect observations of large populations, not guide individual health advice. Because BMI uses no information other than a person’s height and weight, it provides no insight into the amount of fat an individual carries or how that fat might impact their health.
Where did BMI come from?
BMI is based on Belgian mathematician Adolphe Quetelet’s attempt around 200 years ago to describe a “normal” human body. He observed that following puberty, “the weight increases as the square of the height.” In 1972, physiologist Dr. Ancel Keys proposed this observation could be used to assess body fat. Since that time, we’ve been told that BMI above the “normal” range puts us at risk for a wide range of obesity-related conditions, such as diabetes, high blood pressure, metabolic syndrome, heart disease, stroke, cancer, and other serious health problems.
Is there a better way to measure obesity-related risk?
Recently, the American Medical Association (AMA) adopted a new policy recognizing several problems with the use of BMI in clinical settings, including racial bias as well as failure to account for individual differences and variations across sexes and age groups. Due to BMI’s questionable value in individual assessments, the AMA advises doctors to use the measurement in conjunction with other measurements of risk such as visceral fat, body adiposity index, relative fat mass, body composition, waist circumference, and genetic and metabolic factors when assessing obesity-related health risks.
Body composition analysis (BCA) provides precise information about the proportion and location of body fat, giving healthcare providers a window into actual health risks rather than leaving them to guess based on broad generalizations. BCA uses a low-dose X-ray procedure commonly known as a DEXA scan to create images of the body, allowing doctors to identify the proportion and location of body fat as well as the proportions of muscle and bone. This is much more information than can be gathered through methods like waist measurement or body adiposity indexing.
How does body composition relate to individual health?
Because BCA provides a detailed picture of body composition, it avoids the perils of BMI, which can both misidentify and fail to identify body fat-related health risks. A 2016 report published in the International Journal of Obesity found that out of 40,000 people studied, just 70% who had normal BMI were also within healthy ranges of heart and metabolic measures like blood pressure, cholesterol, and insulin resistance. 47% of subjects classified as “overweight” and 16% of those with “obese” BMI measures also fell within those healthy ranges. While there is clearly a correlation here, BMI is far from an exact predictor of cardiovascular and metabolic health.
How can BCA guide better health care?
BCA does more than measure body fat; it distinguishes between visceral and subcutaneous fat, which can have very different health impacts. Visceral fat is what doctors worry about. This is the fat that surrounds internal organs and may not be visible from the outside. Subcutaneous fat resides just under the skin and is generally considered harmless; in fact, it could even play a protective role in a person’s health. With BCA, patients get specific information about their body composition, and doctors can give them more individualized guidance about how best to safeguard their health. Because of its ability to visualize bone, muscle, and fat, BCA can play a vital role in managing weight loss, guiding athletic training, and supporting healthy aging.
Iowa Radiology offers DEXA body composition analysis for patients in the Des Moines area. Appointments are scheduled for 30 minutes, and the painless, non-invasive scan takes only 3 to 5 minutes. To learn more about imaging at Iowa Radiology, visit our services page.
Resources
American Medical Association. AMA adopts new policy clarifying role of BMI as a measure in medicine. Published June 14, 2023. Accessed December 21.2023. https://www.ama-assn.org/press-center/press-releases/ama-adopts-new-policy-clarifying-role-bmi-measure-medicine.
Ametefe CY, Osei-Yeboah J, Owiredu WKBA, et al. Performance of Body Adiposity Index and Relative Fat Mass in Predicting Bioelectric Impedance Analysis-Derived Body Fat Percentage: A Cross-Sectional Study among Patients with Type 2 Diabetes in the Ho Municipality, Ghana. BioMed Research International. Vol. 2023, Article ID 1500905. https://dx.doi.org/10.1155/2023/1500905.
Cerqueira MS, Araújo dos Santos C, Silva DAS, et al. Validity of the Body Adiposity Index in Predicting Body Fat in Adults: A Systematic Review. AN/Adv Nutr. 2018;9(5):617–674. https://dx.doi.org/10.1093/advances/nmy043.
Chen, A. If BMI Is the Test of Health, Many Pro Athletes Would Flunk. NPR. Published February 4, 2016. Accessed December 21, 2023. https://www.npr.org/sections/health-shots/2016/02/04/465569465/if-bmi-is-the-test-of-health-many-pro-athletes-would-flunk.
Livingston M, Castro-Sloboda G. Your BMI Doesn't Matter as Much as You Think. Here's Why. CNET. Published January 19, 2023. Accessed December 21, 2023. https://www.cnet.com/health/nutrition/your-bmi-doesnt-matter-as-much-as-you-think-heres-why/.
Shmerling RH. How useful is the body mass index (BMI)? Harvard Health Publishing. Published May 5, 2023. Accessed December 21, 2023. https://www.health.harvard.edu/blog/how-useful-is-the-body-mass-index-bmi-201603309339.
Tirrell M. Doctors urged to move beyond BMI alone as a health measure. CNN Health. Published June 19, 2023. Accessed December 21, 2023. https://www.cnn.com/2023/06/19/health/bmi-doctors-health-measure-wellness/index.html.
Villines C. Ways to lose subcutaneous fat. Medical News Today. Updated December 21, 2023. Accessed December 21, 2023. https://www.medicalnewstoday.com/articles/319236.
