Alternative body mass index in the test

AI-supported combination of body weight and blood values ​​also includes health markers

BMI 2.0: Scientists have developed an alternative to the common body mass index (BMI) – the biological BMI. This is not only based on body weight in relation to height, but also includes numerous biomarkers in the blood. According to the analyses, this reflects the actual condition of a person better than the usual BMI and bypasses previous misclassifications. In addition, it also makes the positive effects of diets and lifestyle changes more visible, according to the team in “Nature Medicine”.

For decades, the body mass index (BMI) has been a common tool to classify people as underweight, normal weight, overweight , or obese. It can be calculated by dividing your weight in kilograms by your height in meters squared. People with a BMI between 18.5 and 25 are considered normal weight, those with lower values ​​are considered underweight and those with higher values ​​are considered overweight. The threshold for obesity is a BMI of 30. A high BMI is also considered a risk factor for a number of chronic diseases, including diabetes, cardiovascular disease and cancer.

BMI graph
The traditional BMI formula misattributes many people.© CollageM/ Getty images

A new formula for BMI

But the BMI calculation with the previous formula is problematic because it assigns almost a third of all people to the wrong weight class. This is the case, for example, with athletes with a high muscle percentage. The muscle mass makes them heavier than average, which makes them appear overweight on paper. Even when people are actually overweight or obese, the current BMI often falls short. Because studies show that there are different forms of obesity and overweight, which differ in key characteristics and risk factors.

To take these differences into account, researchers led by Kengo Watanabe from the Institute for Systems Biology in Seattle have now developed a new, biological body mass index. To do this, they carried out extensive blood tests on around 1,000 people of various weight classes, which recorded more than 1,100 blood components, including proteins and metabolic products, as well as genetic risk values.

In a further step, the scientists developed adaptive algorithms that identified the most meaningful values ​​in the analysis results and, on this basis, determined a “BMI 2.0”, the so-called biological BMI.


Biological BMI causes shifts

The result: The biological body mass index via blood test and artificial intelligence classified around 30 percent of the test subjects in a different BMI class than the conventional calculation. For example, there were people who would traditionally be considered normal weight but still ended up with a biological BMI of over 25. The reason: Her health was worse than her weight would suggest.

Conversely, people who would be classified as obese based on the traditional BMI also ended up in the normal weight class on the biological BMI. They were healthier than their weight would suggest. According to the research team, the biological BMI is therefore better suited to get a holistic picture of a person’s state of health.

Better indicator of change

“We now have the ability to use advanced molecular measurements as a more comprehensive representation of a person’s metabolic health that can be used to make more accurate clinical recommendations for individuals,” says Watanabe’s colleague Noa Rappaport. According to this, obesity, metabolic diseases and chronic diseases can be treated in a much more individual and targeted manner on the basis of the biological BMI.

According to the researchers, the biological BMI also offers advantages for overweight people who are in the process of losing weight. If the test subjects in the study changed their lifestyle for the better, i.e. they exercised more or ate healthier, then the biological BMI responded better and fell earlier than the conventional one. Unlike just looking at the scales, the BMI 2.0 reflects health changes more clearly. The analyzes also showed which blood values ​​react more quickly to positive lifestyle changes and which only with a longer delay.

More motivation to lose weight

This feedback is also important for people who, despite diet and exercise, initially do not lose weight or only lose weight very slowly. “Monitoring blood composition during a weight-loss program could help participants keep motivated because they would get quick feedback on how the lifestyle changes are affecting their health, even if they’re not losing weight,” the research team writes.


According to the scientists, such a delayed weight loss is not that unusual. As part of their study, they were able to observe that obese but “internally” healthy people often only lost weight slowly. (Nature Medicine, 2023; doi: 10.1038/s41591-023-02248-0 ) 

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