Evaluate your ideal weight: BMI, body mass index

By Cristiano Antonino On Jan 13, 2023

BMI (Body Mass Index) is a body density indicator useful for understanding if we have an adequate weight for our height: in short, it is a parameter that relates a person’s weight to his height

In fact, it is one thing if a person 160 cm tall weighs 100 kg, another is if that weight refers to a person two meters tall.

The BMI therefore takes into consideration the distribution of weight over a more or less extensive surface – i.e. a body

The BMI was created in 1832 by Adolphe Quetelet, a Belgian mathematician and statistician, thanks to anthropometric studies of human growth, based on the observation that weight grows with the square of height – the BMI was in fact known as the Quetelet index.

This indicator was revived about a century later, in the 1970s, and used under the name of Body Mass Index by the physiologist Ancel Keys and used in studies on obesity.

Calculating the Body Mass Index or Body Mass Index is very simple: the value is obtained by dividing the weight expressed in kg with the square of the height expressed in meters.

BMI = weight in kg / H² in meters

For example, the BMI of a person 180 cm tall and weighing 75 kg will be obtained by dividing the weight value (75 kg) by the height squared (1.80² m) as follows:

75kg / 3.24m = 23.5BMI

The result of this formula classifies the subject in an area of body density which can be: thinness; underweight; normal weight; overweight; first-degree obesity; second-degree obesity; third-degree or morbid obesity.

BMI CONDITION

< 16.5 SEVERE THINNESS

16-18.49 UNDERWEIGHT

18.5-24.99 NORMAL WEIGHT

25-29.99 OVERWEIGHT

30-34.99 OBESITY CLASS I (mild)

35-39.99 OBESITY CLASS II (average)

> 40 CLASS III OBESITY (severe)

A person 180 cm tall and weighing 75 kg with a BMI of 23.5 (75 kg / 3.24 m = 23.5 BMI) will therefore be of normal weight.

The ranges in this table have been defined by studies of risk of morbidity and mortality which appears to be the lowest between 18.5 and 25, in fact considered the norm.

WHAT DOES THE BMI TELL US ABOUT OUR HEALTH?

The BMI, also called Body Mass Index (BMI) is an indicator of the risk of disease and mortality, but must be considered together with other parameters to avoid errors:

the abdominal circumference
body composition (measurement of water, lean mass and fat).

The BMI does not take into account differences in sex, age and ethnicity: it therefore has important limitations.

It may have a certain degree of reliability in population studies, but on the individual the error may not be so negligible: in fact, the BMI does not distinguish fat mass from lean mass.

That is, he does not understand whether the weight refers to fat or muscles, therefore he could misclassify some subjects, such as body builders for example.

IS THERE A DIFFERENCE BETWEEN MEN AND WOMEN?

Since it does not consider fat mass and lean mass and does not take into account gender and age, the Body Mass Index must always be associated on the individual with the abdominal circumference:

men accumulate abdominal fat more easily – more dangerous for health and cardiovascular risk.
women frequently have a buildup on the buttocks and hips (gynoid buildup) with less impact on health.

Considering only the BMI, in women there is a risk of overestimating the effect of fat mass.

BMI: WHAT ABOUT CHILDREN?

BMI is not a usable parameter for individuals under the age of 18.

In these cases, in fact, it is necessary to resort to the appropriate growth curves that relate the subject’s age, sex and weight in the appropriate growth charts.

WHAT TO DO IF YOU HAVE A NON-NORMAL WEIGHT BMI

As we said, the BMI alone is not sufficient to establish whether or not a subject is in a state of health, but it does provide a fairly useful indicator.

The adoption of healthy lifestyles, including correct nutrition, good sleep habits and physical activity, can help to achieve and maintain good health and a Body Mass Index within optimal parameters.

In more complex cases, where willpower alone is not enough, it is possible to consult a specialist.

BMI: How To Calculate Body Mass Index

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