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Why calculate BMI?
BMI is a widely used measure because it’s easy, convenient, and non-invasive. Anyone can quickly calculate their BMI at home with no information other than their current height and weight. You can calculate it yourself using a formula, or you can use any number of free online BMI calculators. While this can give most people a general idea of whether they are carrying extra weight, it falls short in some important ways.
What does BMI leave out?
Body Fat Proportion
First, BMI provides no information about how much fat a person is carrying. It’s commonly known that muscle is denser than fat, so a person who is very muscular can be classified as overweight or even obese when looking at BMI alone; conversely, a person with very little muscle mass can appear to be within a healthy weight range while actually carrying an unhealthy proportion of body fat. This is clearly exemplified in cases of elite athletes like British Olympic runner Christine Ohuruogu and NFL quarterbacks Tom Brady and Brett Favre, whose BMIs label them all as overweight.
Body Fat Location
The BMI measurement becomes even more problematic when it leads people to believe they are healthy when their body fat actually puts them at risk for serious illness. This can be the case in so-called “skinny fat” individuals—people who appear thin and have BMI in the healthy range but whose bodies contain dangerous amounts of visceral fat. Studies have shown that people with this condition of “normal weight obesity” are at high risk for cardiovascular disease and metabolic problems, which can cause premature death. In fact, a 2008 study concluded that ¼ of normal-weight adults in the U.S. have some sort of heart health problem.
People who eat more sugar and refined grains have been found to store more visceral fat. Visceral fat can coat organs and appear less prominent that subcutaneous fat, which resides just beneath the skin and may actually provide some protective benefit to those with high visceral fat. Visceral fat has been linked to a number of health issues, including heart disease, diabetes, and stroke.
How can I better understand my body composition?
A few options exist that provide more information about body composition. Calipers measure subcutaneous fat but don’t provide any direct information about visceral fat. Body fat scales and hydrostatic weighing have become popular and can provide more accurate measures of overall body fat, but these methods give no information about the location of body fat and can sometimes produce inaccurate results.
Dual-energy X-ray absorptiometry body composition analysis (DXA BCA) uses low-dose X-ray technology to provide accurate information about how much fat your body contains and where it’s stored. This can be useful not only for assessing how much and what type of fat your body is carrying but also in identifying areas of muscular imbalance, informing your nutrition and exercise plans. If you’re just about to undertake a new nutrition and exercise regimen, getting a baseline DXA BCA before you begin and repeating the scan throughout your program can give you an accurate picture of your progress toward your goals, helping to motivate as well as guide your efforts. Some providers, like Iowa Radiology (using BodyLogicTM technology), offer single scans or a series of three to help you track your progress.
What is DXA body composition analysis like?
DXA BCA is a quick and simple test. The exam itself takes just three to five minutes and involves lying face up on the exam table while an arm of the machine passes over your body. The technologist can review your results with you immediately following the scan, and some offices will also send a report to your health care provider of choice with no referral needed.
A DXA body composition analysis can provide you with more insight into your weight and overall health than looking at BMI alone. For more information about ways to keep your health in check, subscribe to our blog.
Resources
Armstrong, Brock. Is BMI an Accurate Way to Measure Body Fat? ScientificAmerican.com. https://www.scientificamerican.com/article/is-bmi-an-accurate-way-to-measure-body-fat/. Published June 22, 2019. Accessed March 13, 2020.
Bruso, Jessica. Foods to Avoid for Visceral Fat. Livestrong.com. https://www.livestrong.com/article/39247-visceral-fat-foods-avoid/. Published February 26, 2016. Accessed March 13, 2020.
Lewis, Tanya. BMI Not a Good Measure of Healthy Body Weight, Researchers Argue. LiveScience.com. https://www.livescience.com/39097-bmi-not-accurate-health-measure.html. Published August 22, 2013. Accessed March 13, 2020.
Porter SA, Massaro JM, Hoffmann U, et al. Abdominal Subcutaneous Adipose Tissue: A Protective Fat Depot? 2009;32(6): 1068-1075. https://dx.doi.org/10.2337/dc08-2280. Published June 2009. Accessed March 13, 2020.
Sifferlin, Alexandra. The Hidden Dangers of “Skinny Fat.” Time.com. https://time.com/14407/the-hidden-dangers-of-skinny-fat/. Published March 12, 2015. Accessed March 13, 2020.
