Is your BMI an accurate reflection of your health?

For decades, health experts have been using the body mass index (BMI) scale as an indicator of body fat distribution and as a predictive factor for overall health outcomes.

But in a new perspective in the journal Science, researchers from the Perelman School of Medicine say that body mass index is not an accurate measure of body fat – and does not account for important factors like proportion of muscles to fat, fat distribution and differences in body composition that have to do with gender or race.

Obesity paradox

Based on recent studies that suggests obesity sometimes protects against death from chronic diseases, the researchers claims that this "obesity-morality" paradox indicates the need for more studies on how BMI is associated with health. Evidence that certain people with normal BMI are metabolically unhealthy and therefore fall under the radar of their doctors until it is too late further complicates the problem, the research team noted.

"There is an urgent need for accurate, practical and affordable tools to measure fat and skeletal muscle and biomarkers that can better predict the risks of diseases and mortality," said study author Dr. Rexford Ahima in a statement.

Population studies on obesity often fail to assess how intentional or unintentional weight loss or gain affects associations between BMI and health risks, the authors noted.

An outdated system?

The medical community had been using BMI calculations since the system was invented by Belgian mathematician Adolphe Quetelet in 1832, but BMI often does not accurately reflect the picture of a person's health, Ahima asserts.

For example, a person can be overweight because of a variety of reasons – genetics, psychological problems, behavioral issues – and they can also carry fat in different areas of the body. Growing research suggests that excess fat around the middle of the body, for instance, could be indicative of health problems. Or a healthy woman of normal weight with large breasts could also get a high BMI reading that suggests she is headed for trouble.

"Advances to improve the measurement of obesity and related factors will help determine the optimal weight for an individual, taking into account factors such as age, sex, genetics, fitness, preexisting diseases, as well novel blood markers and metabolic parameters altered by obesity," Ahima said.

To understand better how BMI relates to chronic disease, research on molecular pathways and metabolic factors that are altered by obesity would be helpful, the authors concluded.

Source: Penn Medicine