New metabolic BMI shows risks that the scales overlook

Anna Sandner

6.2.2026

Translation: machine translated

Researchers from Leipzig and Gothenburg have developed a new metabolic BMI. The metBMI visualises metabolic health and uncovers disease risks where the classic view of the height-to-weight ratio fails. This makes it possible to recognise impending dangers such as diabetes and cardiovascular diseases even before the first symptoms appear.

Imagine you're driving to the MOT. The inspector only looks at your car from the outside, measures the length, width and weight, nods with satisfaction and sticks the sticker on it. She doesn't see that the engine is stuttering and the oil is leaking. Sounds absurd? It is. Nevertheless, our health assessment using the classic body mass index works in a similar way.

The BMI reliably tells you whether you are considered normal, overweight or underweight in relation to your height. It does not tell you whether you are healthy or ill.

The classic: square, practical, inaccurate

The conventional BMI is one thing above all: unbeatably simple. Weight divided by height squared, done. This has been the standard for decades. No expensive equipment or tests are needed, everyone can work it out for themselves at home. Extremely practical.

The problem with this? Complex biology cannot be summarised in such a simple formula. The BMI does not distinguish what your weight consists of. It lumps the 90 kilos of a well-trained athlete (muscles) into the same pot as the 90 kilos of a person with a lot of dangerous belly fat. For your health, however, it makes a decisive difference whether the weight is due to fat or muscle. And above all: BMI is blind to your metabolism. It shows you whether you fit into dress size S or L. But it says nothing about how your cells work or whether inflammation is already forming in your blood vessels.

This would be acceptable if the value only served as a rough guide. However, in the healthcare system, the BMI often acts as a hard «gatekeeper»: access to stomach reductions, modern weight loss drugs or inclusion on the waiting list for donor organs is often strictly dependent on BMI limits. Here, a simple calculation formula decides medical fates, although it is not sufficiently meaningful for this complex risk assessment. The new metabolic BMI could change this. It is not a tool for the calculator in the bathroom at home, but a precise clinical instrument to visualise real health risks where the classic BMI is blind.

The metBMI: a look under the bonnet

The fact that the traditional BMI is used as a harsh assessment criterion in medicine means that quite a few high-risk patients are simply overlooked. The «TOFI» types (Thin Outside, Fat Inside), who are slim but have an unhealthy metabolism. This is exactly where the metabolic body mass index comes in.

Dr Rima Chakaroun, researcher at Leipzig University Medicine and lead author of the study, summarises it like this: «Our metabolic BMI reveals a hidden metabolic disorder that is not always visible on the scales. Two people with the same BMI can have completely different risk profiles depending on the function of their metabolism and fat tissue».

Instead of scales and measuring tapes, the researchers from Germany and Sweden used high-tech analyses (mass spectrometry) on almost 2,000 people. They were looking for metabolites - tiny degradation products of our metabolism, the «exhaust gases» of our internal engine, so to speak. Out of 1,000 substances, they filtered out 66 that are extremely accurate predictors of how healthy someone is. The result is the metabolic BMI (metBMI).

The results showed that people of normal weight with a high metBMI had a risk of diabetes and heart disease that was up to five times higher than people of the same weight but with a low metBMI.

The trail leads to the gut

The researchers found explanations for this by taking a closer look at the gut. People with poor metBMI often had an impoverished microbiome. They lacked bacteria that convert fibre into valuable butyric acid. Butyric acid nourishes the intestinal wall and has an anti-inflammatory effect. If it is missing, the metabolism comes under stress - regardless of what the scales show.

The results of the study are promising: lifestyle determines metBMI more than genes. A gut-healthy diet can improve metabolic status, even if weight stagnates.

Anna Sandner

Senior Editor

Anna.Sandner@galaxus.de

Science editor and biologist. I love animals and am fascinated by plants, their abilities and everything you can do with them. That's why my favourite place is always the outdoors - somewhere in nature, preferably in my wild garden.

---

News + Trends

From the latest iPhone to the return of 80s fashion. The editorial team will help you make sense of it all.

Show all

These articles might also interest you