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Childhood obesity can be measured with various national and international standards and cutoff points resulting in important differences in prevalence estimates. However, across all data there is a rapid increase globally in the numbers of children affected. Although still at a high level, childhood obesity levels seem to have stabilized in some high income countries. However, the prevalence of obesity in children is rapidly increasing in many low- and middle-income countries (LMICs), particularly those undergoing rapid demographic and socioeconomic transitions. There is substantial evidence that early life influences, in particular prenatal environmental conditions such as maternal adiposity, play an important role in the development of obesity in children. Childhood obesity is a serious health concern itself and children have an increased risk of developing asthma, bone and joint problems, type 2 diabetes, hypertension, and cardiovascular disease later in life. Pediatric surgeons have to manage a greater number of obese children who are more likely to have surgery related complications. Identification by and awareness among pediatric surgeons will be crucial in optimizing the hospital stay and outcome of these children. Obese children are more likely to become obese adults and have an increased risk for noncommunicable diseases (NCDs) later in life. Early prevention interventions are needed to break the cycle of obesity one generation to another and will be most cost-effective, both in low and high income societies.
KeywordsChildhood obesity Epidemiology Interventions Life-course Noncommunicable diseases Prevention
The worldwide prevalence of childhood obesity has increased at an alarming rate and is now one of the major public health threats (WHO 2014). Globally, the number of overweight children under the age of five is estimated to be over 42 million. Close to 35 million of these are living in developing countries (WHO 2014). There is some evidence that the prevalence of childhood obesity now seems to have stabilized in developed countries, whereas it is rapidly increasing in developing countries (Wabitsch et al. 2014). The reasons for this apparent stabilization are not known.
Children who are overweight or obese can suffer from emotional and social problems, and it has become a daily social problem for health professionals, teachers, and parents (Lobstein et al. 2003). The burden of childhood obesity not only involves increasing prevalence levels in children but also the much earlier onset of comorbidities such as type-2 diabetes, heart disease, and some types of cancer (Han et al. 2010). Overweight and obese children are likely to stay obese into adulthood and more likely to develop noncommunicable diseases like diabetes and cardiovascular diseases at a younger age (Nader et al. 2006).
The alarming rise in obesity levels in children and the health problems that follow have profound economic consequences, such as the burden on health services, rise in medical costs and impact on national budgets, as well as loss of personal income (John et al. 2010). Although the increasing levels of obesity prevalence in many developed countries, such as the United States, may have stabilized (Ogden et al. 2012), obesity levels are rapidly increasing in most parts of the world, especially LMICs (Han et al. 2010; Ng et al. 2014).
Overweight and obesity, as well as their related diseases, are largely preventable, and prevention of childhood obesity therefore needs to be given a high priority (WHO 2014). There is now substantial evidence on the influence of early life risk factors and the risk of childhood obesity (Mameli et al. 2016) and disease later in life and the time before conception offer perhaps one of the most promising targets for preventive interventions (Hanson et al. 2012). LMICs need immediate action to implement effective public health programs from high income countries, adjusted to their local context, to prevent further increases in childhood overweight and obesity rates and possibly reach a plateau at a lower level (Wabitsch et al. 2014). This chapter will discuss the different measures and main mechanisms of childhood obesity, international growth standards, health consequences, and prevention strategies and also compare obesity rates across the world.
Measuring Overweight and Obesity in Children
Overweight and obesity are generally defined as abnormal or excessive fat accumulation in adipose tissue that may impair health (WHO 2000). Ideally, adipose tissue would be measured directly, but this is not possible in vivo (Lobstein et al. 2003). In the past, obesity was defined as visible excess of body fat and while clinically evident obesity was diagnosed easily it was not that straightforward for determining overweight children (Lobstein et al. 2003). Several indirect methods have been developed to evaluate body composition and specifically total fat mass, such as underwater weighing, magnetic resonance imaging (MRI), and dual-energy X-ray absorptiometry (DEXA) (Lukaski 1987). However, many of these laboratory techniques are expensive and invasive and not suitable for large population-based studies or screening programs (Lahti-Koski et al. 2004). Anthropometric measures are thus the most widely used methods for defining overweight and obesity in large-scale population studies. Body mass index (BMI) is most commonly used as a surrogate for body fat content and a simple index of weight-for-height to classify overweight and obesity in adults. BMI has internationally agreed thresholds, with overweight a BMI between 25 and 30 kg/m2 (WHO) and obesity a BMI greater than 30 kg/m2. For children and adolescents, anthropometric measures for diagnosing overweight and obesity is more difficult because of the influence of age, gender, pubertal status, and race/ethnicity on growth (Han et al. 2010).The most used ones are subcutaneous skinfolds, different ratios of height and weight, and body circumferences (WHO Multicentre Growth Reference Study Group 2006).
Indices Based on Weight for Height Measures
A variety of different terms, metrics, and cutoff points have been used to define childhood overweight and obesity based on weight and height, such as 110–120% of ideal weight for height, or weight-for-height greater than 1 or 2 standard deviations above a predefined mean, or gender-specific 85th and 95th percentiles of body mass index-for-age (Ogden et al. 2010). There are international (International Obesity Task Force (IOTF) and World Health Organization (WHO)) and national growth references (Center for Disease Control (CDC), Spain-SRS, Italy-Luciano) to describe and assess overweight and obesity in children. These growth references show weight, height, and BMI for children by age and gender in use, with different cutoff values and give therefore slightly different estimates of overweight and obesity prevalence (Quelly 2014). In 2002, the International Obesity Taskforce (IOTF) developed international standards for classifying overweight and obesity which enabled comparison of prevalence globally (Nader et al. 2006). The IOTF recommend using these international growth charts and age and gender specific cutoff points because, on average, they correspond to the adult thresholds. The IOTF classification has been shown to have high specificity but low sensitivity (Han et al. 2010). However, many countries continued to use their own country-specific charts, including the United States (CDC), where standards are based on a national survey from early 1960s, i.e., before the current epidemic.
In 2006, the World Health Organization released new international Child Growth Standards for children 0–5 years, based on data from international optimally nourished breast-fed infants (WHO Multicentre Growth Reference Study Group 2006). The standards depict normal early childhood growth under optimal environmental conditions and can be used to assess children everywhere, regardless of ethnicity, socioeconomic status, and type of feeding. Naturally, there are individual differences among children, but across large populations, regionally and globally, the average growth is remarkably similar. For example, children from India, Norway, and Brazil all show similar growth patterns when provided healthy growth conditions in early life. The WHO 2006 Child Growth Standard shows that differences in children’s growth to age five are more influenced by nutrition, feeding practices, environment, and healthcare than genetics or ethnicity (WHO Multicentre Growth Reference Study Group 2006). There are also reference charts available for children aged 5–19 years (based on a revision of US data collected in 1977 adapted to match the standards for 0–5-year-olds). Since 2006, there are 125 countries that have adopted the WHO standards, and many countries switched from weight-for-age only to multiple indicators. Weight-for-age was adopted almost universally, followed by length/height-for-age (104 countries) and weight-for-length/height (88 countries). Most countries opted for sex-specific charts and the z-score classification (22).
Consequences of Different Growth Standards
There are important differences in the prevalence of overweight and obesity between the WHO, IOTF, and national reference standards due to the choice of cut-offs and to design and characteristics of used samples (de Onis et al. 2007; Monasta et al. 2011). Overweight and obesity prevalence estimates among children based on IOTF and CDC definitions are substantially lower than estimates based on WHO definitions (Monasta et al. 2011; Wijnhoven et al. 2013). This means that using the WHO standards will result in lower rates of undernutrition (except during the first 6 months of life) and higher rates of overweight and obesity than when CDC or IOTF standards are used (de Onis et al. 2007). This finding was confirmed in a study comparing the WHO 2006 Child Growth Standard and the UK 1990 growth standard. It showed by the WHO 2006 that standard infants were less likely to be classified as underweight or having poor weight gain in the first year but more infants would be classified as overweight in the preschool years (Wright et al. 2008).
Several studies reporting on the prevalence of childhood obesity in high income countries have used the IOTF cutoff points. However, IOTF can only be applied to children 2–18 years old where the WHO reference covers the full spectrum of childhood. When comparing the CDC with the WHO standards, the CDC charts reflect a heavier, shorter sample than the WHO standards (O’Neill et al. 2007). The WHO standards weight-for-age mean Z-score seem to better track healthy breast-fed infants track and would be the better tool for monitoring the rapid and changing rate of growth in early infancy (de Onis et al. 2007).
Skinfolds and Body Circumference
BMI is of limited use in capturing subtle alterations in growth and body composition, such as total and regional body fatness, limb/trunk length, and skeletal muscle mass (SMM), which are needed to establish the early life origins of noncommunicable diseases such as type 2 diabetes (Lobstein et al. 2003; McCarthy 2014). Triceps and subscapular skinfold measurements assess the thickness of subcutaneous tissue and reflect fatness primarily and are a useful addition to the battery of growth standards for assessing childhood obesity (O’Neill et al. 2007). Waist circumference is a validated measure to measure deep subcutaneous as well as intra-abdominal fat accumulation, which represents risk of ill health (Cole et al. 2000). Waist circumference is a measure of abdominal fatness in children and is associated with higher fasting glucose and insulin concentrations and altered lipid profiles (Brambilla et al. 2013). Waist circumference is now endorsed by the International Diabetes Federation and National Institute for Clinical and Health Excellence for diagnostic and monitoring purposes (McCarthy 2014). In addition, chest circumference is associated with obesity in young children and is positively correlated with rapid growth. Therefore, chest circumference may be a useful marker for rapid growth and may help clinicians to identify obese children at 3 years of age (Akaboshi et al. 2012).
Global Burden of Childhood Obesity
There are only a few datasets describing the cross-sectional development of BMI values in children over several decades before 1980. These data show a rather stable or slowly increasing prevalence of childhood obesity (Wabitsch et al. 2014). Since 1980, however, there has been a dramatic increase in prevalence of overweight and obesity in children and adolescents in developed countries: the Global Burden of Disease Study 2013 reported that 24% of boys and 23% of girls were overweight in 2013 compared to 17% of boys and 16% of girls in 1980 (Ng et al. 2014). Along with the increase in obesity prevalence between 1980 and 2000, the overall mean BMI values in children increased and the heaviest children had become even heavier (Skinner et al. 2014). Starting at around the year 2000, childhood obesity levels seem to have stabilized in several developed countries (Han et al. 2010; Olds et al. 2011; Wabitsch et al. 2014). This was in contrast to projections of continued increases, such as in the United States where prevalence rates of obesity in children were expected to reach 30% by 2030. The plateauing of childhood obesity rates was more marked in girls than boys and prevalence was declining in most preschool children (aged 2–5 or 6 years) (Olds et al. 2011). It is unclear why saturation has been reached in developed countries, but it might result from cumulative public health programs for obesity prevention (Waters et al. 2011; Wabitsch et al. 2014). However, it should be noted that prevalence rates are still at a high level and still significantly higher than before 1980. Also, extreme obesity is still increasing, despite the declining rates for lower obesity categories (Wang et al. 2011; Skinner et al. 2014).
Childhood Obesity in LMICs
In contrast to these findings in high income countries, the prevalence of overweight and obesity is still rising in children and adolescents in many LMICs (Popkin et al. 2012). From 1980 to 2013, prevalence rates in these countries have increased from 8% to 13% for both boys and girls (Ng et al. 2014). However, there are now several LMICs countries that describe prevalence rates of childhood obesity of more than 15% in children and adolescents, such as Mexico (42%), Brazil (22%), India (22%), and Argentina (19%) (Gupta et al. 2012).
Many LMICs are undergoing rapid demographic and socioeconomic changes that have caused changes in dietary habits and sedentary lifestyles. This has led to a shift in consumption patterns from a traditional low fat and high fiber diet to more “Western” diets that are energy dense, low fiber diet, the “nutrition transition”(Drewnowski et al. 1997; Popkin 2001). Initially, it was thought that in high-income countries obesity levels would be highest in poor people and rural areas and that the opposite was to be observed in low and middle income countries. However, emerging evidence suggests that the burden of childhood obesity in developing countries is shifting toward the urban poor (Popkin et al. 2012).
Childhood Obesity and Social Economic Class
The causal direction of the relationship between childhood obesity and social economic class is complex (Wang et al. 2012). In general, socioeconomic groups with greater access to energy-dense diets are at increased risk of being obese than their counterparts. Since 2005, the prevalence of childhood obesity is increasing in children in all socioeconomic groups in developed countries, but mostly in children from low socioeconomic groups (Grow et al. 2010). Initially, there was a greater increase among higher-SES children in developed countries, especially after 1997, when income inequality dramatically increased (Singh et al. 2008; Wang et al. 2012). However, it seems that in developed countries the gap has closed in the wrong way and children in more deprived population groups have now overtaken those in least deprived population groups (Brunt et al. 2008). Obesity, overweight and central obesity, and sedentary behavior coexist with undernutrition, such as in urban areas in India (Singh et al. 2007).
Pathways to Childhood Obesity
It is now recognized that there are several pathways to childhood obesity, which can be summarized in the categories below. These are often based on the concept that aspects of the prenatal environment and even aspects of parental lifestyle and nutrition preconception (Dean et al. 2013) lead to childhood adiposity and obesity. In turn, childhood obesity tracks into obesity in adolescents and adults, conveying greater risk of NCDs (Nader et al. 2006). It should be noted, however, that measurement of adiposity in young children in the postinfant phase may not give reliable estimates of risk, as it is normal for children to lose and then regain weight (the so-called adiposity rebound) at different rates, making comparative measurements hard to interpret.
One of the pathways leading to childhood obesity involves developmental mismatch. The theory of predictive adaptive responses (PARs) posits that prenatal environmental conditions such as maternal diet induce phenotypic changes in the developing offspring, which uses these cues about the current environment to predict aspects of its future postnatal environment (Gluckman et al. 2005). PARs have arguably evolved because this opportunity to alter phenotype may provide a Darwinian fitness advantage in the predicted environment (i.e., survival to reproductive age and successful reproduction). PARs may therefore potentially become maladaptive later in life should there be a disparity between the anticipated and actual environment. This may arise from cues being inaccurately transmitted (due perhaps to placental dysfunction), or not reflecting the later environment, due to socioeconomic and nutritional transition between generations. The latter can occur in the case of maternal ill-health such as preeclampsia, because the mother consumes an unbalanced diet not representative of the population or, most importantly in the contemporary context, because diet and lifestyle influences change between one generation and the next. The outcome is a situation of developmental mismatch, where the offspring phenotype is not best suited to its environment, leading to greater risk of disease (Gluckman et al. 2007). Maternal undernutrition is relatively common in developing countries, and this is associated with gender equality issues; in developed countries, despite plentiful food diets are often unbalanced in relation to both macro- and micronutrients (Hanson et al. 2009). Even within the normal range of Western diets in the UK, a less prudent diet before and in early pregnancy is associated with alterations in fetal hemodynamics leading to greater hepatic blood flow and less shunting through the ductus venosus, and this is associated with greater adiposity at birth and age 4 years in the child (Godfrey et al. 2012). The improvements in socioeconomic status, migration, and urbanization lead to nutritional transitions which exacerbate this problem (Popkin et al. 2012).
Studies of the biology of fetal growth have now shown that the process of maternal constraint (evolved maternal and uteroplacental factors limiting fetal size to minimize risk of obstructed labor occurs in all pregnancies to a greater or lesser degree (Gluckman et al. 2004). Greater maternal constraint predisposes the offspring to mismatch. Such constraint is greater in primiparous pregnancies of great relevance to countries such as China where family size has been limited (Reynolds et al. 2010). Greater constraint is also associated with shorter maternal stature, multiple conception, at the extremes of maternal age, and with unbalanced diet, smoking, or some drugs. Each of these situations has been associated with a greater risk of childhood overweight or obesity.
Maternal Obesity and Gestational Diabetes Mellitus
There is now much concern about the effects of maternal adiposity and gestational diabetes mellitus (GDM) on risk of overweight or obesity in the offspring (Gaillard et al. 2014). Pregnancy is a state of modest insulin resistance, which favors hyperglycemia and adiposity in the offspring (Hanson et al. 2012; Ma et al. 2013). Maternal obesity is also associated with increased birthweight independent of GDM (Black et al. 2013) with fetal hyperinsulinemia and obesity from the neonatal period through to childhood and young adulthood, graded across the whole range of maternal BMI (Modi et al. 2011). Higher gestational weight gain is also correlated with BMI in early adulthood independently of maternal obesity. Once again these processes appear to operate across the range of BMI and gestational weight gain, at least in Western populations; there does not appear to be a threshold BMI or weight gain at which a pathological as opposed to a physiological process operates.
The mechanisms underlying these pathways are now increasingly recognized to involve epigenetic processes – work which was first demonstrated in animal studies (Lillycrop et al. 2005) but is now shown to be applicable to human development. For example, maternal diet in early pregnancy is associated with changes in the methylation of part of the genome associated with the RXRa gene and in turn with degree of fat mass in the child at age 6 or 9 years (Godfrey et al. 2011). Epigenetic changes in metabolically relevant genes are now also reported for the offspring of GDM pregnancies (Ruchat et al. 2013). Some epigenetic marks, even in blood, appear to be stable through childhood and to relate to childhood fat mass (Clarke-Harris et al. 2014). These may therefore be valuable biomarkers of risk and potentially useful for monitoring their efficacy of interventions .
Reviews on pathways linking overweight/obesity to NCDs show that inflammatory processes are particularly important (Singer et al. 2014). Wider social issues related to pathways involve ethnic differences (Taveras et al. 2013) and amplification by migration in childhood Schooling et al. 2004). The mechanisms by which these process occur, which involve in part mismatch, possibly some genetic factors, and other influences, are not known (Popkin 2001; Han et al. 2010).
Health Consequences of Childhood Obesity
The pulmonary system (obstructive sleep apnea, asthma, exercise intolerance)
CNS/psychological effects (intracranial hypertension – pseudotumor cerebri, reduced quality of life, depression, low self-esteem, social discrimination)
The cardiovascular system (hypertension, dyslipidemia, atherosclerosis, chronic inflammation, coagulopathies, left ventricular hypertrophy)
The renal system (hyperfiltration, glomerulopathy); orthopedic effects (lower limb misalignment, slipped capital femoral epiphysis, Blount’s disease – tibia vera, osteoarthritis, flat feet, ankle strains, increased fracture risk)
The gastrointestinal system (NAFLD, gastro-esophageal reflux, cholelithiasis, vitamin D and iron deficiency)
Endocrine systems (insulin resistance/IGT, type 2 diabetes, PCOS, menstrual abnormalities, hypercortisolism, pubertal advancement)
There are also links to various cancers, particularly of the esophagus, colon, rectum, and kidney (Ezzati et al. 2005; World Cancer Research Fund/ American Institute for Cancer Research 2007). Apart from these distinct clinical conditions, the quality of life is reduced in obese children (Tsiros et al. 2009), making them less likely to be happy and productive adults. The detrimental effects of obesity in terms of social exclusion or victimization in children should also not be underestimated (Voigt et al. 2014). Most of the reviews on health consequences of obesity are derived from developed countries, although the same risks clearly operate in developing countries (Kelishadi 2007) and there are more data for China and Korea (Li et al. 2008; Song et al. 2010).
Childhood Obesity and Surgery Related Complications
The increased risk of complications faced by obese children undergoing surgery is well documented. Obesity is associated with a variety of physiological changes which may impair a patient’s response to surgery. While children and adolescents may experience serious health issues associated with their weight – including asthma, obstructive sleep apnea, bone and joint problems, hypertension, cardiovascular disease, and type 2 diabetes – they are even more at risk during a surgical procedure (Mortensen et al. 2011; Philippi-Hohne 2011). Anesthetic management of the obese child can be challenging and associated with a higher incidence of critical incidents during anesthesia (El-Metiny et al. 2011). Administering anesthesia to children is complex because their airways are still developing and are prone to collapse during the administration of anesthesia, and the risk is increased by obesity. Although children and adolescents receive anesthesia by both inhalation and intravenously, anesthesia is most often given by mask to younger patients, which can pose more risk when the patient is obese. It can also be difficult to find a vein to administer intravenous anesthesia in an obese child. Furthermore, obese children and adolescents are susceptible to other potential complications when undergoing surgery, such as difficult mask ventilation, airway obstruction, oxygen desaturation, bronchospasm, and prolonged awakening from anesthesia. It has been reported that the obese children have a higher rate of oxygen desaturation requiring supplemental oxygen and unplanned overnight hospital admission than normal weight children (Olutoye et al. 2011). Obese children are also more likely to have a prolonged stay in the postanesthetic care unit probably a reflection of the increased incidence of upper airway obstruction (Olutoye et al. 2011; Gleich et al. 2012).
Childhood obesity has also been shown to be associated with increased risks of complications and technical difficulties during and after operative procedures. It is associated with longer hospital stay and higher morbidity (Kutasy et al. 2013). Surgical-site infections following various surgical procedures are more common in obese children compared with nonobese patients. Several studies have reported that obesity is associated with significant changes in cutaneous microcirculation and microcirculation which may contribute to the increased incidence of surgical-site infections (Wagner et al. 2012). With the increasing rates of childhood obesity, pediatric surgeons must appreciate differences in the management and outcomes of these patients with surgical disorders (Ogden et al. 2014).
How Early Should Prevention for Childhood Obesity Start?
Even though recent data suggests that childhood obesity rates have been stabilizing in several high income countries, no countries have had significant decrease in obesity prevalence in the past 33 years (McPherson 2014). Furthermore, rates are increasing dramatically in developing countries (Ng et al. 2014).
Structures within government to support childhood obesity prevention policies and interventions.
Population-wide policies and initiatives that help to create environments that support healthy diets and physical activity, and discourage unhealthy activities, such as legislation, taxes and subsidies, and social marketing campaigns that affect the population as a whole (and specific vulnerable groups).
Community-based interventions that can be adapted to be successful when applied in multiple contexts, including early childcare settings, schools, and other community settings.
Conclusion and Future Directions
Childhood obesity has reached epidemic proportions and calls for prevention and treatment programs to reverse this trend. There is now fundamental understanding of early life developmental factors in determining disease risk. Early interventions will have more impact than later interventions and will be more cost-effective. There are methodological issues that need to be overcome, but there is great potential for interventional approaches to prevent or reverse developmental trajectories leading to obesity. While action and support is needed on the part of health care providers, regional and local government, there is also a need for greater public awareness of the necessity to engage in community intervention programs at many levels. This turn requires programs to promote self-efficacy and empowerment, especially in disadvantaged groups of the population, if a virtuous circle of intergenerational obesity prevention is to be established to counter the vicious circle generating increasing obesity burden which currently operates both in low and high income societies.
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