Metabolic BMI reveals hidden health risks in normal weight individuals

People of normal weight may also be at risk of diabetes and similar diseases. A study from the University of Gothenburg reveals that those with an unexpectedly high so-called metabolic BMI have up to a five times higher risk level.

Conventional BMI offers too limited a view to accurately assess the risks of metabolic diseases, such as cardiometabolic diseases. BMI is based solely on a person's height and weight and provides a value to divide into the categories: underweight, normal weight, overweight or obesity.

Metabolic BMI (MetBMI), on the other hand, identifies obesity-linked changes in metabolism that can be present even at normal weight. The current study, published in Nature Medicine, identifies the magnitude of the risks faced by people whose metabolic BMI is higher than their conventional BMI.

Hidden metabolic disorder

The results show that unexpectedly high metabolic BMI is linked to a two to five times higher risk of a range of diseases and conditions: fatty liver, diabetes, abdominal obesity, insulin resistance, and even predicts poor/limited weight loss following bariatric surgery.

Our metBMI uncovers a hidden metabolic disorder that is not always visible on the scale. Two people with the same BMI can have completely different risk profiles depending on how their metabolism and adipose tissue function."

Rima Chakaroun, researcher at Sahlgrenska Academy, University of Gothenburg and first author of the study

The metabolic BMI developed by the researchers is based on advanced metabolomic analyses - comprehensive measurements of hundreds of small molecules in the blood that reflect cell metabolism. The measurement provides a far more accurate picture of an individual's metabolic health and cardiovascular disease risk than traditional BMI. The study analyzed 1,408 participants.

Linked to gut bacteria

A key finding of the study is a strong link between metBMI and the composition of bacteria in the gut, the gut microbiota. People with higher metBMI had a gut microbiota with reduced diversity and lower potential to break down dietary fiber into butyric acid, which has previously been linked to inflammation and increased disease risk.

The researchers suggest that metBMI could become a tool for identifying people with metabolically unhealthy obesity, even if they do not meet traditional BMI thresholds. Fredrik Bäckhed is a Professor at Sahlgrenska Academy, University of Gothenburg:

"The traditional BMI often misses people who have normal weight but high metabolic risk. metBMI can contribute to a fairer and more accurate assessment of disease risk and thus pave the way for more personalized prevention and treatment."

The study also highlights that genetic factors are less important for metBMI than lifestyle and environment, pointing to the possibility of influencing one's metabolic health through diet, physical activity and gut microbiota composition.

"The metabolites that heavily contribute to the metBMI prediction are in fact modulated or produced by the gut microbiota, making it something of a metabolic dial, says Bäckhed.