BMI

BMI Explained - What is BMI?

BMI means Body Mass Index. It is a tool used throughout medicine and health to determine a person’s weight against their age, sex and height. For adults, a BMI range looks like this:

Under 18.5 – Underweight
Between 18.5 and 24.9 – Healthy weight
Between 25 and 29.5 – Overweight
Between 30 and 39.9 – Obese

Although BMI can be a controversial tool to use due to its inability to assess the density and true composition of body mass, it is a simple and user friendly tool to check health risks associated to weight.

Why is BMI controversial?

The measure of BMI only assesses body mass from calculating weight against height, sex and age and therefore doesn’t give us a true representation of what our body mass is made of. For example, A sumo wrestler and a Rugby player may have the same BMI regardless of the fact that one athletes mass is predominately body fat, where the other one is muscle or; (depending on position) both.

Many people will argue that a Heavy Weight Boxing Champion has a high BMI and therefore contradicts the tool. Heavyweight boxers BMI for example would suggest that they were certainly overweight and maybe even obese. BMI is considered to be a cost effective, easy to use tool which identifies that our bodies are holding excessive mass or not. If we are holding excessive mass, we must be honest in what that mass is, whether it be muscle or body fat. If we can identify that our mass is actually body fat then it would be advised to make realistic lifestyle changes to live a healthier life.

Children’s BMI Centile

Due to the complexities of children gaining weight, aging and growing taller, a child’s healthy weight is a little more complex to calculate. To do this, BMI’s are calculated by centile. For children, BMI centiles show:

Below the 3rd centile – Underweight
Between the 3rd and 91st Centile – Healthy Weight
Over 91st Centile – Overweight
Over 98th Centile – Very Overweight

How is a child’s BMI different?

Measurements of BMI differ between children and adults. Children should grow naturally by gaining gradual height and weight as they get older. Although our bodies are made differently, it is much more likely that young people hold excessive mass from body fat as oppose to muscle. Muscle in children should fully develop through adolescents and close to adulthood.

Children however have an advantage over adults when it comes to reducing BMI. For an adult to reduce their BMI, changed to diet and lifestyle to achieve a deficit in calories through food and exercise is important. Children can adopt the same changes however have another advantage of growing taller as they age. Their frame as they grow means their bodies can hold more natural weight.

It is also very important to take into mind that we should not completely rely on our children growing; and that lifestyle changes are recommended to help reduce BMI to a healthy level as they grow up.

FAQ's

I don’t believe in BMI. Why is this the national measure for weight?

BMI is your Body Mass Index. As children get older their body mass naturally increases. Naturally this should be from muscle, bone and a small amount of body fat. Today’s children are susceptible to growing with excessive body fat which means their mass is higher than where is should be for their age, height and sex. BMI in children takes into account how tall they are, gender, and age. This then provides a centile value which determines how much excessive mass they have. Children who have a BMI centile over the 91st should consider lifestyle changes to ensure they do no go into adulthood overweight where they will be at higher risk of illness and disease.

How can my child’s BMI come down?

Some lifestyle changes can make a huge impact in reducing a child’s BMI centile. Assessing portion control, reducing sugar, managing snacks and increasing fruit and vegetables to the diet can make a big difference. BMI centiles can also come down by maintaining weight. As children grow taller and age, maintaining weight can reduce the centile helping children move towards a healthier weight.

How can I assess my child’s BMI?

You can add your child’s height, weight, age and gender into the Growing Well Growing Healthy App. This part of the app can plot your child’s centile and let you know if your child is overweight. From here you can make a referral or seek information and support from the Growing Well Growing Healthy Team.