An approach to Primary Prevention of Obesity in children and adolescents

(Preconception to 18 years)

Siobhan Ahearne-Smith 18th March 2008

Background

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 foundoverweight/obese.1The true picture of overweight/obese children may however be higher as these figures were based only on 80% participation and research results indicatethat a proportion of children who may be overweight/obese may not have been included in the measurement process.1Further emphasizing that there is an absolute requirement for an approach to primary prevention of child obesity are thedisturbing 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

Definition

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

Classification systems and cut offs

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 85th and 95th 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 91st and 98th 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

Cause of child obesity

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

Consequences of child obesity

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.4Children 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.5However, 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.6Obesity, 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

1: Recommendations for primary prevention

  1. Measurement

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.12Measurement 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.13BMI measurement and plotting should begin at age1 to afford early detection of overweight and obesity. Gender specific BMI charts are availablefrom Document detailing the correct procedures for undertaking measurements:“Guide to Growth Assessment in Hospital and the Community”

  1. Limit the consumption of energy dense foods

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

  1. Follow current dietary recommendations

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

  • Fruit and vegetables: Fruits and vegetables are promoted for the prevention of childhood obesity because of their low energy density, high fiber content and satiety value.27Fruits and vegetables may decrease total energy intake by displacing energy dense foods.12 Fruits and vegetables can be fresh, frozen, canned, dried or juiced. A minimum of 5 servings should be consumed each day. Fruits and vegetables should provide approximately one third of the total volume of food eaten. 34 Further information and portion size recommendations
  • Bread, rice, potatoes and other starchy foods: Meals should be based around foods from this group.35 Foods from this group should provide approximately one third of the total volume of food eaten34and should be included at each meal.35 Eating more foods from this group will help reduce the proportion of fat and increase the amount of fibre in the diet.35
  • Milk and dairy foods: Foods from this group should provide approximately one sixth of the total volume of food intake.343servings per day are recommended for example one carton of yogurt, 150ml milk, small piece (30g) hard cheese.
  • Meat, fish, eggs, beans and other non-dairy sources of protein: Up to approximately one-sixth of the total volume of food consumed should be from this group. 2 servings per day are recommended.34Fish should be consumed twice per week. Oily fish (such as Salmon, Mackerel, Sardines) should be consumed at least once per week, however no more than four servings for boys and two servings for girls.36
  • Foods high in fat and/or sugar: Foods from this group should be limited and only eaten in small amounts. Ideally no more than about one-twelfth of total food intake should be consumed from this group.34
  1. Avoid Snacks that are high in fat/sugar/salt

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

  1. Minimize or eliminate sugar sweetened drinks

Evidence strongly supports a positive association between the intake of calorically sweetened beverages and adiposity in children.27Sugar sweetened beverages currently provide a major contribution to children’s overall calorie intake12,30however they do not give rise to any feeling of satiety. A meta-analysis of studies undertaken over 25years suggests that compensation at subsequent meals forenergy consumed in the form of a liquid could be lesscomplete than for energy consumed in the form of solidfood.32A 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 sugarsweeteneddrink that they consumed every day.31

  1. Have breakfast every day

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.28A 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

  1. Encourage the development of sound dietary practices.

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

  1. Limit the number of meals eaten outside the home

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 1contained 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

  1. Limit portion sizes

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 subsequenteating episodes.19

  1. Participate in 1 hour of daily physical activity

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

4. Minimize or eliminate sugar sweetened beverages

  1. Limit screen time (TV viewing, computer usageetc.) to 2 hour per day

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 toincrease the consumption of fast food in children,possibly through food advertising and/or food messages embedded within program content.37TV 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 Pediatricsrecommends 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

  1. Recommend adequate sleep hours appropriate to child’s age

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

2: Recommendations for primary prevention through the life course

Preconception

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.48It has also been found that women who are obese before pregnancy (regardless of gestational weight gain) are less likely to initiate breastfeedingthan 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

  • 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 12th 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 leastmoderate 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 onesession, or through several shorter bouts of activity of 10 minutes or more. The activity can belifestyle 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 activitya day is necessary to prevent obesity.52

Pregnancy

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.61,62There 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. InEngland and Wales (2005) 8.5% of babies were born LBW from social class 5-8 and 6.5% from social class 1-4.68