BMI Is BS: Why You Shouldn't Let It Affect Your Body Image

BMI, or body mass index, has long been the standard measuring tool for assessing body fat. While there are many sites online that calculate BMI easily, the essential calculation is just one's weight in kilograms divided by the square of one's height in meters. The form of measurement is used on adults over 18 and is meant to indicate weight health. If someone's BMI is less than 18.5, they're considered underweight according to this system. A typical range is anywhere from 18.5 to 24.9, while anything above 25 is deemed overweight and anything over 30 is considered obese, per this standard of measurement.

BMI was developed in Belgium in the 1830s by a mathematician named Lambert Adolphe Jacques Quetelet. Initially called the Quetelet Index, it was revolutionary, but as time has passed, we've come to learn how reductive the form of measurement really is. For one, the research around that time that created the index was based on one demographic. Accredited member of the American Society for Clinical Pathology Sasha Ottey told Endocrine Web, "Most health information (like BMI) is based on white men in the early 1800s, but ethnicity, body type, lifestyle and sex differences need to be included in the care of any patients." Women and people of color have been left out of this research, reducing body health assessment to a simple number that was designed for white men. This leads us to conclude that BMI might not be the most helpful way to relate to our bodies or our sense of health and well-being.

How BMI left behind the female body

Since body mass index was created in the 1830s for the male body, there wasn't a thorough accounting of how this form of measurement would work for a female body. Physiologist Chris Dempers told Cleveland Health, " ... [T]here are key differences across genders that could affect [BMI's] reliability as an indicator of health." Women and men need different amounts of fat in their bodies, and measuring them with the same formula simply isn't as effective. Men need a baseline of 2% to 5% of fat while women need a baseline of 10% to 13% of fat in their bodies. Women typically have a higher percentage of body fat compared to men, while still being equally healthy. Based on this, why would a mathematical equation that was made as a one-size-fits-all umbrella be an accurate predictor of health?

Our bodies are simply too complex to be measured by one mathematical equation. Dempers notes that BMI doesn't account for hormone fluctuation and the significant bodily changes that can come after menopause. "As you go through menopause, your hormone levels decrease," Dempers explained. "As hormones decrease, it causes decreases in muscle mass and increases in belly fat." A woman can have a BMI that falls in a healthy range, when she might actually have more body fat than is healthy. Since the BMI is so reductive, it might not provide accurate information, and can make us feel worse about ourselves or give us an inaccurate sense of our health.

BMI doesn't take into account the modern body

When the BMI was created nearly 200 years ago, the average body was different than it is today. Belgium women in the 1830s weren't as tall or muscular as the average woman is today. Physiologist Chris Dempers explained to Cleveland Health, "BMI was developed 180 years ago, and they were getting most of their data from corpses. Since then, the average height and weight for females and males have also increased."

Female athleticism wasn't understood or practiced in the same way it is today either. A muscular body weighs more, as do strong, dense bones, so someone might register as having a high BMI when their actual body fat might be quite low. On top of this, BMI often gives inaccurate ranges for people of color. Dr. Kunal Shah told VeryWell Health: "BMI has been shown to overstate risk in Black individuals but understates risks in Asians."

So what are better systems for understanding our health in relation to body fat? One way is measuring a person's waist-to-hip ratio, which is one's waist measurement divided by one's hip measurement. A measurement of .85 or higher is considered concerning for one's health. A skin-fold measurement is also useful, as it takes into account the different fat placement in a woman's body compared to a man's. However, even these are simply one tool to assess a complex, changing body. A high BMI shouldn't alter our relationship with our bodies. It's not as comprehensive a tool as we previously thought.