Body mass index, or BMI for short, is commonly used as a quick and easy way to determine if someone is within a healthy weight range. However, many health care professionals have been criticizing this measure for years, and a new study from UCLA researchers supports the argument that BMI is not correlated to overall health. As one of the study’s co-authors, Jeffrey Hunger, put it: “This should be the final nail in the coffin for BMI.”
What’s Wrong with BMI?
Body mass index is a ratio of height to weight (to be exact, it’s a person’s weight in kilograms divided by the square of the person’s height in meters.) It’s intended to provide a quick estimate of a person’s amount of body fat, allowing health care providers to determine if the individual is a healthy weight. In fact, many people center their weight loss or diet plan goals around BMI numbers. A BMI under 18.5 is considered underweight, between 18.5 and 24.99 is considered a normal weight, over 25 is considered overweight, and over 30 is considered obese. However, there are several problems with this method of estimation.
Standard Body Mass Index Graph
First of all, the BMI equation doesn’t distinguish between fat and muscle, meaning that a muscular athlete could be classified as overweight or even obese. The equation also doesn’t take into account location or different types of body fat. Visceral fat, which develops around muscles and organs and can change the way the body balances energy needs, is more harmful than subcutaneous fat, which develops directly under the skin. There’s no way for the simple BMI equation to distinguish between those types of fat that are relatively healthy and those that are less so.
The new study from UCLA suggests that BMI is not just an inaccurate measure, but that there’s no correlation between BMI and overall health. The researchers looked at data from over 40,000 individuals who participated in the National Health and Nutrition Examination Survey between 2005 and 2012, and they found no link between BMI and several important measures of cardiometabolic health, including blood pressure, triglycerides, cholesterol, glucose, insulin resistance, and C-reactive protein. This supports previous research from the study’s lead author, A. Janet Tomiyama, finding no clear connections between weight loss and improvements related to blood pressure, diabetes, blood glucose levels, and cholesterol.
Based on the study, an estimated 54 million Americans who are classified as overweight or obese based on their BMI are actually in good health. Conversely, an estimated 21 million people whose BMI puts them in the ‘normal’ range could actually be considered unhealthy based on cardiometabolic measures. The researchers recommend that people focus on eating well and exercising on a regular basis, rather than obsessing over weight or BMI as a measure of health.