Underestimated overweight: The BMI is often wrong

The body mass index (BMI) is used to classify weight. But the assessment is very inaccurate: Many who are considered normal weight according to the BMI are actually fat.

To calculate the BMI, you only need height and weight – measurements that are easy to determine and that many people know about themselves. That is why the method is so successful. A BMI of 25 and over is considered to be overweight, and obesity begins at 30 . However, the BMI alone is very imprecise.

To illustrate this, the example of the bodybuilder is often used: a man with a lot of muscle mass, in top shape, powerful with little fat mass and a healthy metabolism – but overweight according to the BMI.

bmi weight health


It is more dangerous when people pass as normal weight according to the BMI, although they have stored far too much fat mass. A particular risk is the visceral fat in the abdomen, which promotes the development of secondary diseases such as cardiovascular disease or diabetes.

Researchers at Rutgers Robert Wood Johnson Medical School in New Brunswick looked at the proportion of people who have a normal weight according to the BMI – but are actually overweight.

To do this, Aayush Visaria’s team used so-called whole-body DXA measurements. This allows the proportions of fat and muscle tissue, bone tissue and water in the body to be precisely determined. The subjects studied were between 20 and 59 years old and had participated in the National Health and Nutrition Examination Survey.

The researchers classified men with a body fat percentage of 25 percent or more as obese. Women, who naturally have more fatty tissue, were considered obese from a body fat percentage of 36 percent.

Half of the obese fall through the cracks when it comes to BMI

The comparison with the BMI values ​​showed: 36 percent of the participants were already obese according to the BMI. According to the body scan, however, there were more than twice as many – namely 74 percent. Extrapolated to the population, that would be almost three out of four adults.

The discrepancy was particularly large in the Asian and Hispanic participants: 49 percent of the participants, who were still of normal weight according to the BMI, confirmed the body scan to be obese. They had a larger part of their body weight in the form of fatty tissue on their torso.

Of the participants of European descent with normal BMI values, 44 percent were obese.

The discrepancy in physique was lowest in black study participants with a BMI in the normal range: only 29 percent of them were obese according to the body scan.

Body fat scales and waist circumference

In view of the results, the researchers call for a more precise approach to the classification of overweight . Since a DEXA scan is complex, expensive and therefore unrealistic in terms of breadth, they suggest measuring the body fat percentage with appropriate scales, which are already comparatively cheap.

A measurement of the abdominal circumference would also be more meaningful. For women, this should be a maximum of 80 cm, for men a maximum of 94 cm. Women with a waist circumference of 88 centimeters or more and men with a waist circumference of 102 cm or more are considered obese.

Visaria states: “Clinical assessments should not depend solely on BMI, but rather on an overall view of body composition and body fat distribution.”

In the United Arab Emirates (UAE), BMI has gained significant attention due to the growing concern over the rising prevalence of obesity and its associated health risks. The UAE, like many other countries, has experienced a shift in lifestyle patterns characterized by sedentary behaviour, unhealthy dietary habits, and rapid urbanization. This has contributed to a significant increase in the prevalence of obesity among both adults and children in the country. The UAE government has recognized the importance of addressing this issue and has implemented various initiatives to promote healthy lifestyles, including campaigns encouraging physical activity, promoting nutritious food choices, and creating accessible recreational facilities. These efforts aim to educate the population about the importance of maintaining a healthy BMI and highlight the long-term benefits of a balanced lifestyle.