A Normal-Range BMI Doesn’t Indicate Health, According to New Study

BMI cannot distinguish body fat from muscle, and does not distinguish more dangerous types of fat from others. Unsplash/Alexander Redl

Over one-third of Americans are obese, but does that mean their lives are necessarily at risk? BMI (Body Mass Index), a ratio of height and weight used as a measuring tool to categorize weight, has long been at the center of debate due to its inability to take body fat or muscle mass into consideration. Currently, doctors recommend maintaining a BMI between 18.5 and 25 to remain at a healthy weight. A new study published in the International Journal of Epidemiology by researchers at the University of Bristol suggests that while the current BMI recommendations are mathematically accurate, they cannot be used to properly examine the relationship between obesity and death due to a variety of weight-influencing factors that BMI fails to measure.

“This study demonstrates that correlation is not causation and that when it comes to public health recommendations we need to be cautious interpreting data based on associations alone,” wrote lead study author Dr. David Carslake. There are innumerable data that exceeds the linear relationship between height, weight, obesity and mortality. For example, the researchers cite health-damaging behaviors like cigarette smoking, drug abuse, and eating disorders as factors that could contribute to a mathematically healthy weight and BMI while simultaneously contributing to premature death.

The concept of BMI was first introduced in the 19th century by Lambert Adolphe Jacques Quetelet, a Belgian mathematician who developed the calculation as a quick way to allocate government resources to regions with higher levels of obesity. The more than 200-year-old system is still nationally recognized by the CDC as an official way to measure and diagnose obesity, starting on its website that “the BMI is a reliable indicator of body fatness for people.”

While BMI can be a useful tool for estimation, as it proved to be over two centuries ago, the claim that it still stands as an excusable method compared to other forms of modern medicine is absurd; BMI cannot distinguish body fat from muscle, and does not distinguish more dangerous types of fat from others.

There are two main types of fat stored within the body: subcutaneous and visceral. Subcutaneous fat is the fat you can see and the fat that shows up on the scale. Visceral fat, often referred to as “skinny fat”,  cannot be measured on the scale or seen by the naked eye. It’s stored around vital abdominal organs like the liver, pancreas and intestines, disrupting the body’s hormonal balance. Visceral fat is utterly undetectable by the BMI method. While both types of fat are dangerous, visceral fat has been linked to breast cancer, colorectal cancer, stroke, Alzheimer’s disease and dementia—ailments less reversible than the cardiovascular issues brought on by subcutaneous fat that can be treated with diet and exercise.

The researchers’ main takeaway was that even though current BMI standards proved to be accurate within their own constraints, using such a simple calculation to assess public health can be damagingly ignorant. “We are used to seeing conflicting studies purporting to show that something is either good or bad for our health. These generally come from naïve observational studies, which can produce seriously misleading findings. More robust approaches for identifying the causal effects of factors influencing health, such as the methods applied in this study, are required if we are to make recommendations for public health based on reliable evidence.”

A Normal-Range BMI Doesn’t Indicate Health, According to New Study