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BMI Under Scrutiny: International Commission Calls for a Rethinking of Obesity Diagnosis

Sabine Schneider · August 18, 2025

One billion people worldwide are considered overweight or obese. In this country, that affects about one in four adults. But does that mean everyone affected suffers from symptoms of illness and dies earlier? No.

For several years now, the so-called body mass index—BMI for short—has been the subject of criticism. Until now, this value has been used to determine whether a person is overweight or underweight based on a simple calculation. But what does weight actually tell us about a person’s health?

An international commission (Commission on Clinical Obesity) comprising 56 experts developed new definitions of obesity this year and recommends a revised approach to diagnosis. This is intended to provide more targeted help to severely overweight individuals, while at the same time reducing misdiagnoses and overtreatment. In this context, the experts also hope to reduce the stigma faced by those affected in society.

The BMI Under Scrutiny

How useful is the BMI calculator today?

The internet offers a wealth of websites where you can calculate your own BMI. The simple formula is: weight in kilograms divided by height in meters squared. A value below 18.5 kg/m² indicates underweight; overweight begins at 25 kg/m²; and values above 30 kg/m² have traditionally been diagnosed as obesity. A value of 40 kg/m² or higher is categorized as third-degree obesity.

However, these figures say nothing about a person’s body fat percentage or muscle mass. Someone with a lot of muscle may be mistakenly classified as overweight. Furthermore, some heavier individuals show no symptoms of illness at all, while “normal-weight” individuals with high-risk fat distribution are not even examined in the first place because it goes unnoticed.

The BMI therefore does not allow for conclusions about an individual’s state of health. In the past, this has led to misdiagnoses, unnecessary risks, and costs. Medical resources were depleted—without any benefit to those affected.

Other key factors in body composition include age, gender, and ethnic differences, none of which are taken into account when calculating BMI. For example, in Asia, the BMI threshold for obesity is already 27.5 kg/m², since the population is, on average, slightly shorter than in other parts of the world. However, height ratios are now slowly converging.

According to the commission, an optimized obesity diagnosis should primarily serve the public and alleviate the burden on the healthcare system.

The Role of Visceral Body Fat

To better assess the risk of complications from excess body weight, medical professionals focus on the distribution of visceral body fat—that is, the fat in the abdominal cavity and around the organs. To a certain extent, fat accumulation in this area is normal and healthy; however, amounts exceeding this threshold have been shown to be a major risk factor for cardiovascular disease and type 2 diabetes.

If one relies solely on BMI as a measure, excessive visceral body fat can easily be overlooked.

New Classification of Obesity

The international commission has therefore agreed in its report on new classifications of obesity:

Clinical Obesity

Experts use this term to describe obesity that constitutes a chronic disease, as organ dysfunction is already present due to excess weight. Clinical obesity is regarded as a progressive disease, the further progression of which can lead to severe dysfunction of target organs and life-shortening complications.

In this case, prompt and targeted medical care is crucial.

Preclinical Obesity

This type is not considered a chronic condition, as no organ dysfunction is detectable. In this case, there is only an increased health risk, which can be reduced through preventive measures and careful counseling if necessary.

In order to make an individualized diagnosis—which is the Commission’s primary concern—other parameters must be examined, not just the BMI.

“A thorough and balanced definition of obesity is long overdue in order to address the medical and socioeconomic challenges,” explains Prof. Stefan Richard Bornstein, a member of the commission and director of the Center for Internal Medicine at the Carl Gustav Carus University Hospital in Dresden, as well as a researcher at the German Center for Diabetes Research (DZD).

Step by Step Toward an Individualized Diagnosis

The experts advocate for a multi-phase diagnostic approach to clinical obesity. The first step involves taking a medical history and conducting a physical examination. This is followed by a series of standard laboratory tests, including a complete blood count, blood glucose measurements, a lipid profile, and kidney and liver function tests. If necessary, further diagnostic tests are performed.

In the end, the experts presented 18 criteria for determining clinical obesity. All of these are signs that indicate organ or tissue dysfunction, as well as severe limitations in daily life caused by excess weight. The parameters include, among others, elevated blood pressure, lymphedema, shortness of breath, etc.

Modern Alternatives to BMI

Is the BMI calculator still useful at all? The Body Mass Index can still serve as an initial indicator of a potential health condition or as a basis for initiating further examinations; it is particularly useful for values above 40 kg/m², as obesity in this range is generally associated with serious health consequences.

In contrast, bioelectrical impedance analysis and the waist-to-hip ratio are considered modern alternatives for more accurately assessing one’s health status.

Bioelectrical Impedance Analysis (BIA)

This analysis can determine body fat percentage, muscle mass, and body water content in just a few minutes and is completely painless. Disadvantages: The measuring devices are relatively expensive, and the result may differ from the actual value depending on stomach contents. Therefore, no meal should be consumed before the measurement.

Waist-to-Hip Ratio (WHR)

This very simple measurement method compares the waist circumference to the hip circumference. Both are measured with a tape measure, and the waist measurement is divided by the hip measurement. This provides a good estimate of visceral fat.

Conclusion

The BMI calculator is insufficient for diagnosing obesity, as the values do not provide insight into an individual’s health. According to the panel, a distinction should be made between chronic disease with organ dysfunction and obesity, which is considered only a risk factor for secondary diseases but has not yet caused any impairment.

Using a series of diagnostic criteria, the international commission aims to facilitate the diagnosis of clinical obesity requiring immediate treatment. In cases of preclinical obesity, counseling is recommended, along with further preventive measures only if necessary.

Through this distinction, the experts hope to quickly improve the individual situation of patients, relieve the burden on the healthcare system by reducing misdiagnoses, and protect those affected from unnecessary risks.

If you are overweight and would like to gain clarity about your health status, please contact obesity centers.

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