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BMI for children: everything you need to know about growth charts

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BMI for children: everything you need to know about growth charts
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Raising awareness about obesity and trying to combat it starts in childhood.  Body Mass Index (BMI) and growth charts are two useful tools which can be used to detect potential problems of obesity. But how do you interpret the results? When should you be worried?  

Overweight problems in children can be overlooked by parents.  They think, sometimes wrongly, that their baby will slim down as it is just a bit of baby fat. However child obesity remains a serious problem. Like adult obesity, it is considered to be a public health issue.

It is important to make children aware of good food choices and the need to practice a sport regularly to stay healthy.   However referring to growth charts and BMI calculations can help parents to better understand their child’s weight.  You can then try to introduce new daily routines to promote a healthy lifestyle.

How to calculate a child’s BMI?

Calculating a child’s BMI is exactly the same as for an adult.  You need to divide the child’s weight in kilos by their height in squared metres.

IMC = Weight [kg] ÷ (Height [m])²

Make sure you take your height in metres and not in centimetres.  If a child measures 1 m 10 cm you should note down 1.1 m instead of 110 cm.

How do you interpret the results?

Although the formula is identical to the calculation for adult BMI, interpreting the results is different.  For children the reference values vary depending on their age and their sex. These values are reported on a percentile graph which is called a growth chart.
This tool helps to evaluate the child’s nutritional state.  When the BMI is more than 97 percentile the child is considered obese.  In contrast, if the child’s BMI is below 3 percentile it is a warning that the child is severely under weight.

What is a growth chart exactly?

courbe de corpulence imc de l'enfant
© Inpes

In the child’s first year, their growth will take place at an exceptional rate and then slow down at the age of six.  They will continue to grow up until the age of 18.  Between 3 and 5 years old there is a growth inversion: the more fat is present before the age of 5 or 6 years years old, the higher the risk of obesity.

Growth charts can be found in health documents given to parents. They can also be found on the Royal Collage for Pediatrics and Child Health website.

What do you do if your child’s BMI is not normal?

Parents are recommended to follow their child’s BMI very regularly and in discussion with a family doctor. Although it is important to encourage healthy eating and practical sports don’t start a regime without being given advice from your doctor beforehand.

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