The World Health Organisation defines overweight and obesity as a medical condition involving abnormal or excessive body fat build up, that presents a risk to health.

In Wales:

  • around 25% or 1 in 4 of adults aged 16 and over are living with obesity
  • around 12% of children in the reception year of school (aged 4 to 5 years old) are living with obesity. 

There are many complex causes and each cause can play a part. Understanding the causes of weight gain is the first step in weight management. This can help you to take action. It may be something you can do yourself or as a family.

If you have struggled with your weight or your child’s weight for some time or feel that you need extra support then your GP or health professional can help. They can help by supporting you or your child and investigating any related health problems. You can then both work out a management plan.

Weight ranges

Body Mass Index (BMI) is one way used in healthcare as a basic measure of weight and health. BMI is measured by calculating a person’s weight (in kilograms) divided by their height (in metres) squared. BMI is not used on its own to diagnose obesity because other factors, such as your gender, ethnicity, body composition and age should be taken into account.


For most adults, a BMI of:

  • 18.5 to 24.9 kg/m2 is described as a ‘healthy’ weight range
  • 25 to 29.9 kg/m2  is described as an ‘overweight’ weight range
  • 30 kg/m2 and above is described as an ‘obese’ weight range.

You can use the BMI healthy weight calculator to work out your BMI.

Children and Young People

Measuring BMI in children is more complicated because it changes as they grow and mature. BMI centile charts are used to show if children and young people are underweight or overweight for their age by comparing their BMI with the BMIs of other children of the same age and gender. There are different centile charts for boys and girls.

  • A BMI below the 2nd centile may reflect undernutrition, but may simply reflect a small build
  • A BMI above the 91st centile suggests an overweight weight range
  • A BMI above the 98th centile suggests a very overweight or obese weight range.

The BMI centile chart 2-20 years can be accessed from the Royal College of Paediatrics and Child Health website.

Why weight range is important

Carrying excess weight can have implications for physical and mental health.

Living with obesity may be caused by or affect mental health. The most immediate concern for children can be how it affects their confidence or weight related bullying.

It also affects quality of life for some people. People often say they find parts of their everyday life more difficult. Examples are if they find it hard:

  • to tie their shoe laces
  • play with other children or with grandchildren
  • to move around.

A BMI in the obese range is one of a number of reasons associated with health problems, such as:

  • type 2 diabetes 
  • coronary heart disease 
  • some types of cancer, such as breast cancer and bowel cancer
  • stroke
  • osteoarthritis
  • gastroesophogial reflux disease (heart burn)
  • obstructive sleep apnoea
  • pregnancy complications.

If you are from a Black, Asian or other ethnic group, you may have a higher risk of developing some long-term (chronic) conditions, such as type 2 diabetes. Those with a BMI of 23 kg/m2 or more are thought to be at increased risk and those with a BMI of 27.5kg/m2 or more are thought to be at high risk.

Why waist size also matters

Measuring waist circumference is a way of helping to assess health risk associated with living with overweight or obesity in adults.  Combining this with BMI can give an overall better picture as to whether your current weight might be affecting your health.

A high waist measurement and high BMI could be a sign of a higher risk of developing type 2 diabetes, cardiovascular disease, impaired blood fats (lipids) for example.

For men, a waist circumference below 94cm (37in) is ‘low risk’, 94–102cm (37-40in) is ‘high risk’ and more than 102cm (40in) is ‘very high’. For women, below 80cm (31.5in) is low risk, 80–88cm (31.5-34.6in) is high risk and more than 88cm (34.6in) is very high. These are the guidelines for people of white European, black African, Middle Eastern and mixed origin.

For men of African Caribbean, South Asian, Chinese and Japanese origin, a waist circumference below 90cm (35.4in) is low risk, and more than that is ‘very high risk’ (there isn’t a ‘high risk’ category). For women from these groups, below 80cm (31.5in) is low risk, and anything above is very high risk.

You can use the British Heart Foundation waist measurement guide or Diabetes UK waist measurement guide to help you work out your waist measurement.

Causes of obesity

Obesity is a complex condition caused by many factors that may combine with each other. These include

  • genetics and family history
  • hormones
  • previous attempts to lose weight
  • other health conditions
  • medications
  • mental health 
  • trauma
  • what and how much food is eaten
  • physical activity levels
  • time spent being inactive such as screen time
  • lack of sleep
  • income
  • access to services
  • where you live and your work, school, community and social environments.

Weight management

The best way to manage your weight depends on your individual and family needs and circumstances. For many people, stabilising weight gain can be the first step.

Often this will require identifying and addressing the reasons for excess weight gain. 

It is important to acknowledge what you are already doing or have done in the past to manage weight and what works well for you, or your child and your family.

You may now want to consider:

  • Setting a goal about what small changes you will aim to make or continue. You may only need to make one small change or you may need to make a number of small changes.
  • Think about situations that make it difficult to stick to your goals. Plan in advance what you are going to do in those situations so you can stick to your goals.
  • Get support from friends and family, or others taking steps to manage their weight.

Me and My Health

If you have a long-term physical or mental health condition, this scheme aims to help you and your carer to provide clear information to health and care staff who may need to visit your home in an emergency. For more information see here.


As children are still growing, stabilising weight gain as the child grows is recommended rather than weight loss. This is often described as ‘growing in to their weight’.

For children, a family approach is encouraged, where all family members make healthy changes. These healthy changes could include:

  • healthy eating such as eating more fruit and vegetables and mealtime habits
  • increasing activity
  • reducing the amount of screen time
  • bedtime routines and getting enough sleep
  • what you do during family time.

Your child might be able to come up with ideas for activities they would like to try or get involved in preparing and cooking meals. Examples and guidance for children under 5 can be found on the Every Child Wales website www.everychildwales.co.uk.

Parents and carers can consider how they support their child through their parenting approaches. The Parenting. Give it Time. Website provides free practical and expert guidance and support on parenting challenges such as meal times and screen time.  

Other treatments or dietary approaches might be right for your child and family:

  • if your child has struggled with their weight for some time
  • feel you need additional support
  • feel their weight gain is related to a medical or psychological issue.

These may include:

  • weight management programmes provided by health professionals or other providers
  • specialist psychological support
  • medical or endocrine (hormone) investigations, diagnosis and treatments.

The Welsh Government has provided guidance to weight management providers, to support them to deliver effective services.


When aiming to lose weight it is important to have realistic goals that you can achieve. A weight loss of between 0.5 to 2 pounds (0.5-1kg) on average a week is a realistic target.  However, weight loss can plateau despite your best efforts, so be kind to yourself and keep going.

Other treatments or dietary approaches might be right for you if you:

  • have struggled with your weight for some time
  • feel that you need additional support
  • feel your weight gain  is related to a medical or psychological issue.

 These may include:

  • weight management programmes provided by health professionals, commercial or other providers
  • medications
  • specialist psychological support
  • referral to a specialist service to discuss bariatric surgery.

The Welsh Government has provided guidance to weight management providers, to support them to deliver effective services.


Remember, there will be different approaches for different people, with the right approach depending on your circumstances. It may help to view ‘managing weight’ as something that takes place throughout life.

If you have struggled with your weight or your child’s weight for some time or feel that you need extra support a visit to your GP or health professional will help to discuss your individual needs.

Useful website links:

Obesity UK is a charity that aims to provide help, support and inspiration to those who are struggling with overweight and obesity

British Heart Foundation weight loss hub

British Heart Foundation steps to sustainable weight loss

British Dietetic Association Food Fact Sheet: Weight Loss  

Diabetes UK weight loss planner

Every Child Wales www.everychildwales.co.uk

Parenting Give it Time Parenting. Give it time. | GOV.WALES

Welsh Government (2021) All Wales Weight Management Pathway 2021: Core Components - These documents detail the core components for weight management services in Wales. It provides guidance to those looking to commission weight management services as well as to providers, detailing the minimum service requirements and expectations for weight management services across Wales.

Children Young People and Families


The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website nhs.uk
Last Updated: 14/12/2022 11:16:06