Primary prevention should be the unequivocal first strategy for halting childhood obesity. Statistics from the UK National Child Measurement Programme (2006-07) indicate the prevalence of overweight/obese children at age 4-5 to be 22.9%. Amongst 10-11 year old children 31.6% were found overweight/obese.¹The true picture of overweight/obese children may however be higher as these figures were based only on 80% participation and research results indicate that a proportion of children who may be overweight/obese may not have been included in the measurement process.¹ Further emphasizing that there is an absolute requirement for an approach to primary prevention of child obesity are the disturbing predictions of the Government’s scientific expert committee, the FORESIGHT team, which predicts that, by 2050, 55% of boys could be overweight or obese and 70% of girls overweight or obese.²

Obesity is at its simplest excess adiposity, thus a definition requires a way to measure adiposity and a cutoff to identify at what point adiposity becomes excessive³, posing significant risks to health. Body Mass Index (BMI) has traditionally been the method used as a proxy for adiposity. (BMI = weight/height²). BMI is the internationally recommended indicator of overweight and obesity in healthy individuals.⁹ 

 

There are three different classification systems to define child obesity currently in use in the UK. The 1990 UK National BMI percentile charts¹⁰ are the most commonly used to report the National picture. The classification uses the 85^th and 95^th percentiles of the 1990 UK data cut off points for overweight and obesity respectively. Two other classification systems are also commonly used.  In clinical practice the 91^st and 98^th percentiles of the UK 1990 National BMI percentile reference charts are used. In addition the International Obesity Task Force classification uses reference data collected from six countries to enable international comparisons.¹¹

 

When an individual is in energy balance (energy intake = energy expenditure) body weight remains constant. However an increase/decrease on either side of the equation can result in changes in body weight. Obesity occurs as a result of a long term positive energy balance, that is, energy intake has consistently exceeded energy expenditure. It is however important to remember that the causes of this energy imbalance can result from a multitude of genetic, biological, psychological, sociocultural, and environmental factors that affect both sides of the energy balance equation and the interrelationships among these factors.²¹

 

Childhood obesity has now become the most prevalent nutritional disease in developed countries.³ In children and adolescents the associated morbidities include hypertension, hyperinsulinaemia, dyslipidaemia, type 2 diabetes, psychosocial dysfunction and exacerbation of existing conditions such as asthma.⁴ Children with severe obesity also commonly experience a range of sleep associated breathing disorders, including sleep apnoea. Studies have shown sleep associated disorders to have a clinically significant negative effect on learning and memory function, in addition to the physical risks they pose to the individual’s health.⁵ However, in children the persistence of obesity into adulthood is the most important concern; the risk of persistence increases with increasing age of the child and severity of obesity. ⁴ Childhood obesity is a risk factor for a number of chronic diseases in adult life including heart disease, some cancers and osteoarthritis.⁶ Obesity, especially severe obesity, is also linked to infertility and an increased risk of complications during pregnancy.⁷Obese children are also more likely to experience psychological or psychiatric problems than non-obese children.⁸

 

Regular and accurate measurement of children should be the first step in the prevention of obesity.  Physicians and allied health care providers should perform at a minimum a yearly assessment of weight status for all children and that this assessment include calculation of height, weight and BMI for age and plotting of those measures on standard growth charts.¹² Measurement of children and plotting of BMI is a vital step in tackling obesity given that research indicates that many parents are no longer able to identify whether their children are overweight or not. Indeed in a cross sectional study of 277 British families within a cohort, only 25% of parents with overweight children recognized that their children were overweight. Even more disturbingly 33% of mothers and 57% of fathers described their children as “about right” when in fact they were obese.¹³ BMI measurement and plotting should begin at age1 to afford early detection of overweight and obesity. Gender specific BMI charts are available from www.healthforallchildren.co.uk. Document detailing the correct procedures for undertaking measurements: “Guide to Growth Assessment in Hospital and the Community”

The macronutrients (carbohydrate, fat and protein) are the energy yielding nutrients. Carbohydrate and protein provide approximately 4 k/cal per gram of metabolisable energy. One gram of fat provides 9 k/cal of metabolisable energy.¹⁵ Fat therefore has a higher energy density than either carbohydrate or protein.There is convincing evidence that a high intake of energy-dense foods promotes weight gain.¹⁶ Energy-dense foods are not only highly processed (low Non Starch Polysaccharides) but also micro-nutrient poor, further diminishing their nutritional value. Energy dense foods tend to be high in fat, (for example butter, oils and fried foods), high in sugars and/or starch, while energy dilute foods have high water content (for example fruits and vegetables).¹⁶

 

Current dietary recommendations are reflected in The eatwell plate³⁶ www.eatwell.gov.uk which aims to represent a proportioned, balanced, healthy diet based on a combination of foods from five food groups for individuals aged 2 and over.

Snacks with high refined carbohydrate and high fat content should be avoided. Instead snacks of whole fruit, raw carrots, celery or similar items should be encouraged. Snacking should be avoided while watching television or playing on the computer.²⁰

 

Evidence strongly supports a positive association between the intake of calorically sweetened beverages and adiposity in children.²⁷ Sugar sweetened beverages currently provide a major contribution to children’s overall calorie intake^12,30 however they do not give rise to any feeling of satiety. A meta-analysis of studies undertaken over 25 years suggests that compensation at subsequent meals for energy consumed in the form of a liquid could be less complete than for energy consumed in the form of solid food.³² A recently published study which was undertaken over a 2 year period found the odds ratio of becoming obese among children increased 1·6 times for each additional can or glass of sugar sweetened drink that they consumed every day.³¹

 

Population-based surveys have revealed that many children, particularly adolescents, miss breakfast and other meals and eat more food later in the day and that this pattern has increased in recent years.²⁸ A pan-European research study conducted in the UK, France, Italy and Sweden which comprised children aged 6-16 years of normal, overweight and obese size found obese children less likely to eat breakfast. Obese children who missed breakfast were found more likely to snack regularly, consuming foods high in fat and calories.²⁹A 5-year longitudinal study examining the association between breakfast frequency and body weight change in adolescents found a significant inverse association between breakfast frequency and BMI.³²

 

Eating meals as a family should be an important part of family life and contribute to the development of sound dietary practices. The family meal can create a meal when food is eaten fairly slowly and satiety may come from a pleasant experience rather than overeating.²⁰ Regular meal patterns are important to ensure cycles of appetite followed by satiety, which train children to recognize when intakes are sufficient. In general three main meals and two or three, modest in energy terms, snacks during the day are recommended for children.²⁰

 

A quarter of families in Britain now eat out at least once a week, with much of the market captured by a handful of popular restaurant chains.¹⁷ An analysis was conducted by a nutritionist on behalf of the Soil Association on children’s menus between April and June 2006 from 10 popular restaurant chains. The restaurants were ranked from 1 (best) to 10 (worst), based on how their food compared to the Governments new minimum standards for school meals. Not one restaurant chain came close to meeting the new minimum school standards for meals. Indeed, the average meal from the restaurant which ranked 1 contained double the school meal saturated fat content. The average meal at the restaurant ranked 8, contained eight teaspoons of added sugar, taking a primary school aged child very close to the recommended maximum for a whole day.¹⁷

 

Concerns about diet are compounded by the trend towards larger portions of many food items, notably soft drinks, savoury snacks, and confectionery- so called “supersize” packs. Food eaten outside the home is frequently offered in extra-large portions, often at minimal additional cost.¹⁸ Experimental studies suggest large portions tend to increase energy intake at a meal, with no increase in satiety and little compensation at subsequent eating episodes.¹⁹

 

It is recommended that children and young people achieve a total of at least 60 minutes of at least moderate intensity physical activity each day.⁴ Moderate intensity physical activity is any activity which causes a child to breathe harder than normal and to become warmer. Moderate intensity activities include brisk walking, swimming, dance, cycling and most sports.¹⁴ The daily physical activity recommendation may be achieved through several short bouts of moderate intensity activity of 10 minutes or more, or by doing the activity in one session.⁴

Television viewing, computer usage and other screen watching can increase child obesity risk via effects on energy intake and energy expenditure. Television and video viewing has been found to increase the consumption of fast food in children, possibly through food advertising and/or food messages embedded within program content.³⁷ TV viewing and related sedentary behavior can compete with physical activity, lowering energy expenditure.³⁸In a large UK cohort of children, the Avon Longitudinal Study of Parents and Children, the odds ratio for obesity at age 7 increased linearly with hours spent watching television at age 3. For children who watched more than 8 hours of TV per week the odds ratio for obesity at age 7 was 1.55.³⁹ The American Academy of Pediatrics recommends no television viewing before the age of 2 and subsequently no more than 2 hours a day for older children. A further recommendation is to not have televisions and other screens in children’s primary sleeping area.⁴⁰

 

Little comprehensive data are available regarding sleep duration over time, but the data available suggest that sleep duration has decreased over the years. Sleep duration would have declined at the same time as the rise in obesity.²²A model has been proposed for the potential mechanism by which short sleep duration could result in obesity. Figure 1

 

Figure 1: The potential mechanisms through which short sleep duration could result in obesity.²²

Within this model two hormones ghrelin and leptin are postulated to play mediating roles. Ghrelin is the only known circulating orexigen or appetite stimulatory hormone, leptin a satiety hormone. A systematic review and meta-analysis conducted to determine whether sleep duration is associated with childhood obesity concluded that there is a clear association between short sleep duration and increased risk of childhood obesity.²³While individual sleep needs can vary, the amount of sleep suggested by sleep experts for particular age groups is:²⁴

18 months – 3 years   12-14 hours/night

3-5 years                     11-13 hours/night

5-12 years                   10-11 hours/night

Teenagers                    9.25  hours/night

 

 

It is important that women who are overweight or obese should aim to achieve a BMI of 20-25 before trying to conceive.³⁴ Adverse perinatal outcomes associated with maternal obesity include neural tube defects, preterm delivery, diabetes, cesarean section, hypertensive and thromboembolic disease.⁴⁷Furthermore, women who are obese before conception tend to gain and retain more weight during pregnancy.⁴⁸ It has also been found that women who are obese before pregnancy (regardless of gestational weight gain) are less likely to initiate breastfeeding than women with a normal BMI before pregnancy. In addition, the duration of breastfeeding was found to be less in women who were obese before pregnancy compared to their normal weight counterparts.⁴⁹

·         It is important to identify women who are overweight or obese as early as possible, and refer them to a registered dietitian who can help them lose weight safely before conception.

 

Women who are severely underweight (BMI <18.5) are also at increased risk for a number of adverse pregnancy outcomes, including low birth weight, preterm birth, and intrauterine growth retardation.^{50, 51}

 

·         Women identified by health care providers as underweight before they become pregnant should be referred to a registered dietitian to receive guidance on how to increase their weight.

 

The Food Standards Agency (2005) has produced guidelines for women on a healthy diet when planning a pregnancy http://www.eatwell.gov.uk/agesandstages/pregnancy/trybaby/

 

·          Eat a well balanced varied diet to ensure an adequate intake of all nutrients

·          Take an appropriate supplement of folic acid from the time of cessation of contraception until the 12^th week of pregnancy. Current DH recommendations are 0.4mg to prevent first occurrence of Neural Tube Defects (NTD). A supplement of 5mg is recommended to prevent NTD in the offspring of men or women with an NTD or where a previous child has had a NTD.

·          Try to eat fish every week and include some oily fish but limit this to two portions per week. Shark, swordfish and marlin should be avoided

·          Limit alcohol intake to 1-2 units per week or avoid it altogether

·          In order to minimize the risk from excessive Vitamin A, avoid liver and liver products such as pate and do not take any supplements which contain Vitamin A or fish liver oil unless medically advised

·          Ensure an adequate iron intake to help build up iron stores

·          Atopic women or those with a close relative with atopy should avoid eating peanuts or peanut products to lessen the risk of peanut allergy.

 

Although preconception nutritional advice for men has been poorly researched, the most prudent preconception nutritional advice for men is to consume a balanced and varied diet, have a moderate alcohol intake and correct grossly abnormal body weight.³⁴

 

Current physical activity recommendations should be adopted for both women and men preconception. For general health benefit, adults should achieve a total of at least 30 minutes a day of at least moderate intensity physical activity on 5 or more days of the week. The recommended levels of activity can be achieved either by doing all the daily activity in one session, or through several shorter bouts of activity of 10 minutes or more. The activity can be lifestyle activities such as climbing stairs or brisk walking, structured exercise or sport, or a combination of these. It is likely that for many people, 45-60 minutes of moderate intensity physical activity a day is necessary to prevent obesity.⁵² 

 

The temporal trend toward higher pre-pregnancy BMI and weight gain during pregnancy appears to be at least partly responsible for the trend toward heavier babies.⁶⁰ Studies have found that high birth weight (> 4 kg) is associated with an increased risk of obesity in childhood and adult life.^61,62 There is also compelling evidence that impaired intrauterine growth and development at a critical period in early life may have permanent effects on structure, physiology and function of a range of fetal tissues and organs resulting in the development of a number of chronic diseases including cardiovascular disease, hypertension, type 2 diabetes and obesity.⁶⁶ This is known as the “fetal origins hypothesis”. Low Birth weight (LBW) (< 2.5kg or 5¹/₂ Ibs) is a significant indicator of impaired intrauterine growth. In England and Wales (2005) 8.5% of babies were born LBW from social class 5-8 and 6.5% from social class 1-4.⁶⁸

 

·         High birth weight and low birth weight may increase risk of childhood obesity.

 

There are currently no official UK recommendations for weight gain in pregnancy.³⁴The recommendations that are prescribed worldwide by obstetricians and healthcare providers based on pre-pregnancy BMI were included in a report by the Institute of Medicine (IOM) in 1990.⁵³

 

·         For BMI in the normal range (19.8-26), a weight gain between 11.5 and 16kg is advised

·         For BMI below 19.8, a weight gain of 1-2kg more than this is encouraged.

·         For BMI above 26, the weight gain should be less than the minimum suggested for a BMI in the normal range.³⁴

 

However Feig and Naylor (1998)⁵⁴ summarized data showing little evidence to advocate such liberal weight gain in well fed Western societies. They suggested that the minimum threshold for maternal weight gain should be 6.8kg and that the IOM recommendations are unnecessarily high. Furthermore they suggested that women with a pre-pregnancy BMI within the normal range should aim for a pregnancy weight gain of between 6.8 and 11.4kg.

 

The IOM recommendations for obese women (BMI > 30kg/m²) do not distinguish between the different classes of obesity, do not include an upper limit and recommend to obese women as a whole to gain at least 15Ibs.⁵⁵ While the IOM recommendations focused primarily on prevention of low-birth-weight deliveries, inadequate gestational weight gain will primarily affect birth weight in underweight and normal weight pregnant women, but by and large, not in overweight and obese women.⁵⁵ Indeed in a large population based cohort, class II and III obese pregnant women who gained less than the recommended 15Ibs had a significantly lower risk of large for gestational age births and the risk for small for gestational age was found to be minimal.⁵⁹

 

There is evidence which suggests that increasing maternal hyperglycemia in pregnancy is associated with an increased risk of childhood obesity at age 5-7 years.⁵⁷ Gestational diabetes mellitus (GDM) affects on average 7% of all pregnancies, however in women who are morbidly obese there is an 8.5-fold increased risk of developing GDM.⁵⁶Obese pregnant women who engage in physical activities during their pregnancies can reduce their risk of developing GDM by 50%.⁵⁸

^·          General dietary guidance during pregnancy should focus on the need for a well balanced, nutrient dense diet which will meet the needs for micronutrients such as iron and calcium without excessive weight gain.³⁴

·         Women should be assessed by 12^th week of pregnancy to identify mothers already overweight or obese.⁷⁶

The Food Standards Agency (2005) has produced general dietary guidance for pregnant women http://www.eatwell.gov.uk/agesandstages/pregnancy/whenyrpregnant/  

·         The Royal College of Obstetricians and Gynaecologists suggest that all women should be encouraged to participate in aerobic and strength-conditioning exercise as part of a healthy lifestyle during their pregnancy.⁶⁷

Breastfeeding: A systematic review of published studies completed in September 2003 found initial breastfeeding protective against obesity in later life. Several biological mechanisms were postulated to explain the association. Breastfeeding affects intakes of calories and protein, insulin secretion, and modulation of fat deposition and adipocyte development.⁶³The duration of breastfeeding and the risk of overweight have also been examined. A meta-analysis published in 2005 concluded that the duration of breastfeeding was inversely and linearly associated with the risk of overweight. The risk was reduced by 4 per cent per month of breastfeeding. The effect lasted up to duration of breastfeeding for 9 months. One of the main mechanisms by which breastfeeding affects risk of overweight was again postulated to be calorie intake- breastfed infants having a lower mean calorie intake compared with bottle fed infants- resulting in a lower body weight gain during the critical neonate period.⁶⁴ 

 

Weaning: The introduction of a variety of foods, tastes and textures during weaning and in early childhood is likely to contribute to a more varied and balanced diet in later life.⁷⁰  

 

 

Rapid weight gain in the first year of life: Evidence from the ALSPAC cohort found rapid weight gain in the first 12months of life to increase risk of obesity at age 7.³⁹

 

Postnatal catch-up growth: Intrauterine restraint of fetal growth can result in postnatal catch-up growth. Evidence from the ALSPAC cohort found children who showed catch-up growth between zero and two years were fatter and had more central fat distribution at five years than other children.⁶⁵A subsequent analysis of the cohort data found the risk of obesity at age 7 was over two and a half times more likely in children who showed catch up growth (odds ratio 2.60).³⁹

 

The pre-school years are known to be a key stage in the life course for shaping attitudes and behaviors. Lifelong habits which can have an impact on an individual’s ability to maintain a healthy weight may be established during the pre-school years.⁴ Parents are ultimately responsible for their children’s development but childcare providers may also play an important role by providing opportunities for children to be active and develop healthy eating habits and by acting as positive role models.⁴

There is now compelling evidence that an early age of adiposity rebound is a risk factor for child obesity. Children have a rapid increase in BMI during the first year of life. After 9 to 12 months of age, BMI declines and reaches a minimum, on average, at 5 to 6 years of age before beginning a gradual increase through adolescence and most of adulthood. The point of maximal leanness or minimal BMI has been called the adiposity rebound.⁶⁹ Evidence from the ALSPAC cohort found early adiposity rebound to be independently associated with obesity at age 7. Children with early adiposity rebound before 5 years 1 month were twice as likely to be obese at age 7 compared with children with an adiposity rebound after 5years 1 month. Children with very early adiposity rebound, by 3 years 7 months, were fifteen times more likely to be obese than children with an adiposity rebound after 5years 1 month.³⁹

 

 

Some parents have an unrealistic idea of how much their toddler should eat and may encourage or force feed the child to eat more. There are a number of signals toddlers use to indicate they have had enough food: ³⁴

 

The school years are known to be a key stage in the life course for shaping attitudes and behaviours. School aged children are ultimately dependent upon parents, carers and schools for their food and availability to physical activity; therefore they have the power to influence appropriate eating and physical activity choices.

 

 

Adipose stores increase rapidly in adolescence, so it is no surprise that this stage of life is one of the key points for the development of obesity.³⁴ The British Medical Association suggested that the main factors which have contributed to the rapid rise in obesity in this group are a growing reliance on fast foods, soft drinks and sweets coupled with a more sedentary lifestyle.⁷⁴ Adolescent sedentary behaviour has been found to correlate with parental sedentary behaviour.⁷⁵

 

 

Obese adults who were overweight as adolescents, have been found to have a higher incidence rate of weight-related ill health and a higher risk of early death than adults who became obese in adulthood.⁷³ 

                                                                                                                                                                                           

 

Twin and adoption studies have demonstrated that genetic factors play an important role in influencing which individuals within a population are most likely to develop obesity in response to a particular environment. A review of twin studies suggests that genetic factors explain 50-90% of the variance in BMI.²⁵ A UK twin analyses of BMI and waist circumference in a population based sample of 5092 twin pairs born between 1994 and 1996 found the effect of heritability on BMI to be 77% and 76% for waist circumference.²⁶  

Family studies generally report estimates of parent-offspring and sibling correlations in agreement with heritability of 20 to 80%.²⁵ Results from the Health Survey for England (2006) found parental BMI a significant predictor of overweight including obesity among children aged 2-15. Boys living in overweight/obese households were more likely to be overweight/obese than boys from normal/underweight households (odds ratio 1.32). For girls, living in overweight/obese households had over three times the odds of being overweight or obese compared with girls from normal/underweight households (odds ratio 3.03).⁴¹

 

NB: The genetic environment is undoubtedly important and worthy of considerable interest in the epidemiology of obesity. However, the genetic background to obesity, which is largely outside the scope of interventions, should not overshadow the fact that the epidemic increase in the prevalence of obesity world-wide must relate more to changes in the environment than to changes in human genes.²⁰

The obesity epidemic is a growing problem in all socioeconomic groups in the UK. There is however some social class gradient in childhood obesity. Results from the Health Survey for England (HSE) ⁴³ -analyzed using the national statistics socioeconomic classification- (NS-SEC), showed the lowest social class had more obesity than the highest; levels of childhood obesity were lowest among managerial or professional households (12.4%) and highest among semi-routine and routine households (17.1%). This said the second highest social class (16%) was found to have very nearly as much obesity as the lowest.⁴²  

In an annual report by the Chief Medical Officer⁴⁴ the prevalence of obesity was stated to be almost four times more common in Asian children than white children.¹⁸ Analysis of the HSE found the prevalence of overweight (including obese)among Black African (42%), Black Caribbean (39%) and Pakistani (39%) boys, was significantly higher than that of the general population (30%). Prevalence was found to be highest in Black Caribbean (42%) and Black African (40%) girls, who had a markedly higher prevalence than that of the general population (31%).⁴⁵

Obesity is more common in people with learning disabilities than in the general population.⁴In children with learning disabilities, obesity (based on the 95^th percentile for age) has been estimated to be 24%.⁴⁶

Children with a physical disability may be at increased risk of obesity, particularly in terms of mobility, which makes exercise difficult.¹⁸

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

provided as ethanol or carbohydrate in fluids. Physiol Behav 59: 179–87