In many obese people, the roots of their disorder can be traced back to childhood. Obesity tends to persist through life. While most obese infants will not remain so, they are at increased risk of becoming obese children. These children are in turn more likely to become obese adolescents, who are then very likely to remain obese as adults. Evaluation and treatment of obesity in childhood offers the best hope for preventing disease progression with its associated morbidities into adulthood.

Epidemiology

The persistence of obesity into adulthood depends on several factors, including the age at which the child becomes obese, the severity of the disease and the presence of obesity in at least one parent. Overweight in a child under three years of age does not predict future obesity, unless at least one parent is also obese. After age three, however, the likelihood that obesity will persist into adulthood increases with the advancing age of the child and is higher in children with severe obesity in all age groups. After an obese child reaches six years of age, the probability that obesity persists exceeds 50 percent, and 70 to 80 percent of obese adolescents will remain so as adults. The presence of obesity in at least one parent increases the risk of persistence in children at every age.

Pathophysiology

A person gains weight when energy input exceeds energy output. Energy input is food. Several studies have shown that, on average, obese children do not consume significantly more calories that their thin peers. Energy output comprises the basal metabolic rate, the thermal effect of food and activity. The thermal effect of food is the energy required to absorb and digest meals. Of these variables, activity is the one least influenced by genetic inheritance and is therefore the one most susceptible to change. By measure, 3,500 calories is equivalent to one pound; thus, an excess of only 50 to 100 calories per day will lead to a five- to ten-pound weight gain over one year. As a result, a relatively small imbalance between energy input and output can lead to significant weight gain over time. In fact, most obese children demonstrate a slow but consistent weight gain over several years.

Evaluation of Obese Children

Only a small percentage of childhood obesity is associated with a hormonal or genetic defect, with the remainder being idiopathic in nature. Obese children should be evaluated for associated morbidity. This includes an assessment of cardiac risk factors, weight-related orthopedic problems, skin disorders and potential psychiatric sequelae. Cardiac risk factors include a family history of early cardiovascular disease, high cholesterol and blood pressure levels, cigarette smoking, the presence of diabetes mellitus and decreased physical activity. The National Cholesterol Education Program recommends that physicians screen all obese children over two years of age for elevated cholesterol levels. Obese children also have increased average blood pressure, heart rate and cardiac output when compared to non-obese peers. Tobacco use should be ascertained in all young people, as this represents an independent risk for cardiovascular disease. Finally, the presence of diabetes should be considered in all morbidly obese children. While overt type 2 diabetes mellitus is rare in childhood, hyper-insulin emia and glucose intolerance are nearly universal in morbidly obese children. The child's level of physical activity should be assessed, not only for cardiac risk evaluation, but also to help guide future treatment. Television viewing patterns should be reviewed, since television viewing has been shown to be associated with obesity in childhood. Because they carry excess weight, obese children are at increased risk for orthopedic problems. Obese children are also more prone to skin disorders than are non-obese children, especially if deep skin folds are present. It is essential to address psychiatric problems, including depression, poor self-esteem, negative self-image and withdrawal from peers

Facts about Childhood Obesity

Over the last 20 years, rates of obesity in children have risen greatly in many countries around the world, leading some researchers to speak of an 'international epidemic of childhood obesity'. In the ten-year period from 1985 to 1995 the level of combined overweight/obesity in Australian children more than doubled, whilst the level of obesity tripled in all age groups and for both sexes. In 1995, the proportion of overweight or obese children and adolescents aged 2-17 years was 21% for boys and 23% for girls. The proportion of obese girls aged 7-15 years increased dramatically from 1.2% in 1985 to 5.5% in 1995, and the proportion of obese boys increased from 1.4% to 4.7%. The rate of increase in Australia appears to be accelerating sharply when viewed in a historical perspective. Obese children have a 25-50% chance of progression to adult obesity and it may be as high as 78% in older obese adolescents. Obese adults who were overweight as adolescents also have higher levels of weight-related ill health and a higher risk of early death than those obese adults who only became obese in adulthood. The prevention and management of obesity in children is a priority as there is a high risk of persistence into adulthood. Weight gain and obesity develops when the energy intake from food and drink exceeds energy expenditure from physical activity and other metabolic processes. The trends in these behaviors are not encouraging. For example, mean intake of energy increased by over 10% among Australian children aged 10-15 years between 1985 and 1995. Physical activity levels in Australian adults have declined in the last decade, as in most other countries. There is a lack of survey trend data for children, however, a 1997 survey of NSW Year 8 and 10 students showed that girls were involved in lower levels of vigorous activity than boys and less than 70% of girls remained adequately active over winter. Particularly low rates of adequate activity were seen in girls from Middle Eastern and Asian cultural backgrounds, with further significant declines between Years 8 and 10.Data from the NSW Child Health Survey 2001 found 40% of children, aged 5-12 years, reportedly watch two hours or more of television or videos a day on average and 15% are reported to play computer games for an hour or more a day on average. Such sedentary leisure time pursuits are now widely available to children and are replacing more traditional active pastimes.