Excess weight and obesity (children)


Content last reviewed: 10 April 2017

Obesity is a complex problem with many drivers, including our behaviour, environment, genetics and culture. However, at its root obesity is caused by an energy imbalance: taking in more energy through food than we use through activity. Physical activity is associated with numerous health benefits for children, such as muscle and bone strength, health and fitness, improved quality of sleep and maintenance of a healthy weight. There is also evidence that physical activity and participating in organised sports and after school clubs is linked to improved academic performance. Long-term, sustainable change will only be achieved through the active engagement of schools, communities, families and individuals (1).

In Central Bedfordshire the level of excess weight for children aged 4 to 5, is 19.6% (England avg 22.1%) and children aged 10 to11, is 29.4%. (England avg 34.2%).

The causes of obesity are extremely complex encompassing biology and behaviour, but set within a cultural, environmental and social framework. Although personal responsibility plays a crucial part in weight gain, human biology is being overwhelmed by the effects of today’s ‘obesogenic’ environment, with its abundance of energy dense food, motorised transport and sedentary lifestyles. As a result, the people of the UK are becoming heavier simply by living in the Britain of today. This process has been coined ‘passive obesity’. For the majority of people excess weight gain is the result of eating more calories than needed and/or undertaking too little physical activity to match calorie intake.

Overweight and obesity are clinical terms that describe a level of body fat which can lead to increasingly adverse effects on health and wellbeing. Levels are typically determined via Body Mass Index (BMI), a measure of weight (kg) divided by height (m²) with the answer given in units of kg/m². The value given places an adult into one of the following categories:

BMI Range


Table 1: NICE Clinical guidance. Source: NICE Clinical guidance reference guide 2 obesity (2006)
<18.5 Underweight

18.5 - 24.9

18.5 - 23

Healthy weight (white European)

Health weight (Asian)

25 - 29.9

23 - 27.5

Overweight (white European)

Overweight (Asian)

30 - 34.9


Obesity I (white European)

Obesity I (Asian)

35.9 - 39.9 Obesity II
>40 Obesity III (Morbidly obese)


For Asian populations risk of adverse effects appears to begin from a lower BMI value of 23kg/m² (2).

In children BMI has the potential to be less accurate and there is not a single definition applied worldwide.

In England child BMI is measured at Reception Year (aged 4-5yrs) and Year 6 (aged 10-11yrs) through the National Child Measurement Programme (NCMP). The measurement is carried out in the same way as for adults but the values obtained are given as percentiles (or centiles) plotted against a 1990 population sample reference curve. Population measurement values are shown in the table below.

BMI Percentile  Classification
Table 2: NCMP population monitoring. Source: National Child Measurement Programme
≤2nd Underweight
˃2nd but ˂85th Healthy weight
≥85th but ˂95th Overweight
≥95th Obese

However clinical cut off values are different to the population monitoring levels reflecting the higher level of confidence required for individual measures.

Table 3: Clinical setting. Source: National Child Measurement Programme
≥91st but ≤98th Overweight
≥98th Obese

Complications in measuring children at Year 6 (aged10-11yrs) include increasing muscularity and pre-puberty. However, insufficient evidence presently exists to quantify these components.

While overweight and obesity are clinical terms, they have taken socially derogative connotations to a point where stating a person is obese is typically considered offensive. This presents additional challenges in tackling obesity as people are reluctant to acknowledge that they are overweight or obese, and subsequently seek advice. The visual perception of excess weight in children is also hard to recognise as so many children are overweight that it is difficult to see what should be the ‘normal’ example of a healthy weight child.

This can be really hard to spot just by looking at the child. Take a look at the pictures below.

You might be surprised to know that all of the children in the pictures above are outside the healthy weight range for their age and height. In general, our perception of what is a healthy weight for children has changed over the years, making it more difficult to spot. For more information on BMI regarding children go to:- http://www.nhs.uk/Tools/Pages/Healthyweightcalculator.aspx

Risks associated with overweight and obesity.

Obesity is about health, not appearance.

Conditions linked with obesity in adults and the associated lifestyle choices include:-

  • Cardiovascular disease
  • Respiratory conditions
  • Insulin resistance and Type 2 diabetes
  • Certain Cancers
  • Musculoskeletal problems
  • Low self-esteem and depression
  • Psychological and social problems such as stress, stigma, prejudice and bullying

Maternal obesity is associated with increased morbidity and mortality for both the woman and her unborn child (3). Pregnant women who are obese are at increased risk of:

  • Developing temporary diabetes of pregnancy
  • Having a raised blood pressure and pre-eclampsia
  • Having a blood clot in their legs (DVT)
  • Having a large or ill baby needing increased monitoring which can lead to complications in labour
  • Having a Caesarean section
  • Difficulty in siting for an epidural or giving anaesthetic
  • Having a wound infection, leading to a longer hospital stay
  • (Rarely) having complications following surgery and delivery requiring intensive hospital care
  • Having a still birth or intra uterine death

(Bedford Hospital NHS Trust Maternity data 2011)

For more information please see the JSNA chapter on ‘Maternal Obesity’ (pending).

The risks of obesity in children are similar to that of adults, with an additional burden of teasing and discrimination at school.



(1) Childhood Obesity Plan (2016)

(2) CHOO V, 2002, WHO reassesses appropriate BMI for Asian population. The Lancet 20, 360 (9328):225

(3) Saving Mothers Lives 2003-2005. London: CEMACH; 2007

Last updated Thursday, 20th April 2017