Body mass index

Source: Shutterstock

It is very useful to know your own body mass index o BMI (Body Mass Index, BMI): this is a valid way to evaluate your body weight. In particular, through a formula that uses weight and height it is possible to know this fundamental parameter for the purposes of an estimate of one's physical health. 

Let's try to understand specifically what the BMI is, what the formula is, why it is necessary to respect the correct caloric needs and what is the perfect BMI for adults and children.

In this article

  • Body mass index, what is it
  • BMI: formula
  • BMI and calorie needs 
  • Body mass index, when it is perfect in children 

Body mass index, what is it

Having a healthy weight means that you own the right amount of fat in relation to your body mass. Healthy weight allows you to feel energetic, reduces health risks, helps prevent premature aging and improves quality of life.

Through the scale it is possible to know the total weight, including bones, muscles and fluids. But it doesn't reveal how much fat it is carrying. The most accurate way to know is to do a professional body fat analysis using a reliable estimation method - this can be costly and difficult.

A simpler tool is the measurement ofbody mass index (BMI). It is a mathematical formula that takes into account both weight and height. Although BMI (or BMI) does not accurately distinguish between fat and muscle, it more closely reflects body fat measurements versus total body weight.

BMI provides generic - but fairly accurate - god data to most people health risks in relation to weight.

Read also: The pregnancy diet: daily and weekly menu

BMI, formula

In the past, a simple formula was used to calculate your ideal weight, the so-called Broca's formula: subtracting 100 from the height expressed in centimeters, the ideal weight was obtained in kilograms.

To date, to calculate the ideal weight, or possibly underweight or overweight, we use thebody mass index.

The body mass index is given by the ratio between the actual weight and the ideal weight of a subject with certain physical characteristics. To calculate it, therefore, it is enough divide your body weight (expressed in kilograms) for the height (in meters) squared.

The number obtained is the BMI and represents a parameter corresponding to the lipid deposits (what we call "fat") of the individual analyzed. Therefore the higher the BMI, the greater the fat accumulated by the subject.

Calculate yours body mass index using the MyModernParents TOOL, entering weight and height.

Read also: Calculate BMI

BMI and calorie needs

Il calorie requirement daily corresponds to the amount of food that must be ingested every day to maintain a stable weight. It is also identifiable as the daily energy contribution - through calories that come from food - necessary to compensate for the daily energy expenditure. 

If you are interested in understanding what the recommended daily calories are based on your gender, age and activity level, the table below may be useful. Remember that this table should only be used as a general reference point, because each person it is metabolically different. For further information it is best to contact your doctor. The suggested calorie ranges were generated using the estimated energy requirement calculation of theIstitute of Medicine.

In particular, the table below shows the daily calorie limit and based on age, activity level and BMI of 21,5 for women and 22,5 for men.

If you intend to lose weight or gain weight, the suggestion is always to be patient and to work with a dietician to find the right personalized plan.

For effective and lasting weight loss, experts recommend choosing low calorie foods but rich in proteins, vitamins, minerals, fiber and other nutrients.

Women (sedentary lifestyle)

  • age 19-30: 1800-2000 kcal
  • age 31-50: 1800 kcal
  • age 51+: 1600 kcal

Women (lifestyle with moderate activity)

  • 19-30:  2000-2200 kcal
  • 31-50:      2000 kcal   
  • 51+:        1800 kcal

Men (sedentary lifestyle)

  • age 19-30: 2400-2600 kcal
  • age 31-50: 2200-2400 kcal
  • age 51+: 2000-2200 kcal

Men (lifestyle with moderate activity)

  • age 19-30: 2600-2800 kcal
  • age 31-50: 2400-2600 kcal
  • age 51+: 2200-2400 kcal
Read also: Celiac disease and children: strict diet and annual checks

Body mass index, when it is perfect in children

How BMI is calculated

For the purpose of identifying the BMI of adults, the World Health Organization uses a reference table within which to enter the data obtained, thus checking the corresponding physical state:

  • Less than 16: severe thinness
  • Less than 18.5: underweight
  • Between 18.5 and 25: ideal weight
  • Between 25 and 30: overweight
  • Greater than 30: adiposity (obesity class 1)
  • Greater than 35: obesity class 2
  • Superior 40: obesity class 3.

The ideal number for a BMI would be from 18.5 to 25, but there are many variations that can affect a person's "absolute" health.

The BMI in children

As for the children, the speech is slightly different. In fact, during the growth phase the various parameters are very variable and related to the sex and age of each child. Therefore, the best way to keep the weight of the little ones under control is to calculate percentiles.

Percentile diagrams are the unit of measurement that is used to establish how the child grows in weight and height. They are made by taking groups of 1000 children of the same age as a term of comparison.

Children are divided according to weight and height, after which they are placed in 100 subgroups each consisting of 10 children. Each of these subgroups is a percentile and each centile is representative of one per cent of the infant population of the age taken into consideration.

In the first centiles, therefore, there are the smallest children, while towards the centile the tallest and largest ones are found. For what concern weight, the reference range is as follows:

  • Less than 5th Percentile: underweight
  • 5th to 85th Percentile: normal
  • 85 to 95 percentile: at risk of being overweight
  • Greater than the 95th percentile: overweight

Most of the infant population is positioned between the 25th and 75th percentiles. Children in the 50th centile are medium-sized children. It could be said, therefore, that their BMI is perfect.

Read also: What are percentiles?

Sources for this article:;

World Health Organization

Istitute of Medicine

  • health and children
  • weight
  • family health
  • bmi calculation
add a comment of Body mass index
Comment sent successfully! We will review it in the next few hours.