The body mass index (BMI) can be calculated by using a formula which relates your weight to your height. The result, a number, can be interpreted to give you an idea of whether you are overweight or obese.
We use the same formula – weight in kilograms divided by height in meters squared – to calculate a child’s BMI. However when interpreting your child’s BMI you must be careful to take into account the child’s exact age and use an appropriate BMI chart for their gender.
The chart below is an example. This chart - produced by the Child Growth Foundation - is for the UK population based on the latest data (collected in 1990).
The normal range changes depending on the age of the child.
So, for example, a BMI of 20 is considered severely obese at age 2 but normal at age 16.
The importance of discovering obesity in a child is related to the connection between many diseases and obesity. Usually the child has simple nutritional obesity – that is obesity as a result of imbalance between number of calories taken in and number of calories burnt.
But sometimes, a child will have a medical reason (e.g. a genetic or endocrine cause) for their obesity and the sooner this is discovered, the sooner treatment can get underway.
So in summary,
- You cannot interpret a child’s BMI without having the BMI charts to refer to.
- The normal range changes according to the child’s age and gender.
- Although nutritional obesity is the most common cause of childhood obesity, obesity may be a symptom of an underlying illness. This can be investigated by a doctor and appropriate treatment directed at the underlying illness may alleviate the obesity.
Rather than give lots of examples, I think it would be more interesting for you to download the charts and analyse where you think your own child is. If you have any questions, feel free to get in touch.