What is the body mass index (BMI)?

Although the health situation of the population already seems poor, unfortunately there are no signs that it will improve in the near future. It is true that we entered the new millennium with the conviction that average life expectancy would only increase, but since 2016 this indicator has stagnated.

1. What is BMI?
2. History of BMI
3. BMI indicators – from underweight to class II obesity
4. What are the exceptions when assessing BMI?

Furthermore, there are increasing indications that there may even be a decline. One factor that will inevitably push entire families and social groups to the brink of good health is body weight. The BMI index is used to assess the risk of health problems related to weight.

What is BMI?

BMI stands for “body mass index”. It is calculated by dividing body weight in kilograms by height in metres squared. It is used to divide adults into groups to facilitate the assessment of the overall health of selected individuals. It has been and continues to be used in primary care, insurance practices and advanced scientific research.

History of BMI

Certain correlations between weight and height were already observed in the 18th century. One of the famous statisticians made the first attempts to describe the average woman and the average man in numbers. Interestingly, BMI was already developed at that time, but it was called the Quetelet index (after its inventor). A little later, in the early 20th century, observations were made regarding the relationship between excess body fat and the incidence of disease and premature death. Quetelet's calculations were then abandoned in favour of a simplified version, i.e. the ratio of weight to height.

It is worth noting that the version of the body mass to height ratio used at that time (from 1959 to 1960) was primarily used by insurance companies, which calculated this ratio to assess the risk of disease and the potential loss of money associated with the payment of medical expenses. Interestingly, in the 1990s, Quetelet's method was revisited because the ‘dry’ weight-to-height ratio proved to be useless. This was supported by the WHO, the World Health Organisation.

BMI indicators – from underweight to class II obesity

BMI divides people into six categories. It is worth knowing that both extremes of this scale can be potentially dangerous to health. This mainly concerns underweight with a BMI of less than 20 and class III obesity with a BMI of over 40. A body weight that gives a BMI of around 20–25 for a given height is considered normal. Overweight, which does not usually cause health problems, is a BMI of around 25-30. Results in the ranges 30-35 and 35-40 are grade I and II obesity, respectively, which may already be a sign of disease.

What are the exceptions when assessing BMI?

It was once believed that BMI could be a good indicator of body fat, but it turned out to be too generalised a parameter to be used for an accurate assessment of body composition. Among other things, it does not take into account a person's bone and muscle mass, which can lead to unreliable results.

For example, people with high bone mineral density and densely packed skeletal muscles are often classified by BMI as overweight or sometimes even obese. BMI is also insufficiently precise in assessing the health and nutrition of children and the elderly.