"Health is a state of physical, psychological and social well-being, not merely the absence of disease".

This simple but precise definition encompasses many of the changes that are taking place in medicine. Illness and disease are negative concepts. This definition describes health as a positive concept. Implicit also is the idea of health as a spectrum. An individual free of disease is not necessarily healthy and most of our patients have the potential to improve their health. The transition from a disease centered reactive approach towards a health centered proactive one is already occurring in family medicine.

Family practitioners are trained to view health as an active process influenced by physical, psychological and social factors. This holistic approach is essential if health is to be optimised. In a previous editorial I discussed the body as a chaotic system in which relatively simple interventions early in the cascade may make significant differences to long-term health.¹ Nowhere is this concept more important than in the management of children.

We are currently experiencing a worldwide epidemic of childhood obesity. Cohort studies show that obese children are significantly more likely to become obese adults. The studies also show that obesity in adolescents is directly associated with increased morbidity and mortality in adult life, independent of adult body weight.²

Obesity in Australian children more than tripled in the decade from 1985 to 1995. Australia is second only to the United States as the most obese nation in the world. Interestingly, although the average weight of an American adult has increased by 4.5kg since 1990, fewer Americans consider themselves to be overweight now than in 1990. This is an example of the drift of social norms. As adults become bigger the norm becomes greater, and the same is true of the expectations of their children. This is a worldwide problem, with the studies in Australia and the USA being reproduced in Asia. In Hong Kong and China we are already seeing the early stages of the obesity epidemic as the traditional local diet is replaced by the worst type of Western diet. Data from the World Heart Federation estimate that between 5-10% of Chinese adolescents are obese with a ten-fold increase over an eight year period. Unlike in the majority of the developed world, obesity in China is more likely to be associated with affluence than poverty.

Obese children are three times more likely to develop hypertension than non-obese children, the risk of hypertension increasing across the range of body mass index. Non-insulin dependant diabetes is being reported at younger ages and is now well recognised in adolescents. Metabolic syndrome increases in incidence with increasing obesity reaching 50% of severely obese children in a recent US study.³ The increasing incidence of hypertension, hypercholesterolaemia and diabetes mellitus associated with metabolic syndrome will ultimately produce an epidemic of disease and illness which can be easily predicted from the known precursors.

The epidemic of obesity is caused by a combination of poor diet and lack of exercise. Advertising has been shown to clearly affect the preferences of children. The more children watch food adverts on television the more snacks and calories they eat (Food Standard Agency UK, December 2003). In 1998 one fast food hamburger chain spent over US$1 billion on advertising and promotion the majority being targeted at children. Schools are becoming less and less healthy environments. It is common in schools in Hong Kong to find vending machines selling carbonated drinks. These have a high glycaemic index and are energy dense. Intake of carbonated drinks is directly associated with childhood obesity.⁴ Children who drink one regular carbonated drink a day have an average 10% more total energy intake than non-consumers.⁵

As energy intake is rising, output is also falling. Studies in modern populations show that the average adult loses the equivalent to two hours of walking per day in energy expenditure simply from labour saving devices. Use of cars, lifts and even remote control units for television and hi-fi mean that modern life has become more sedentary. The paradox is that in order to increase health most individuals need to actively seek out ways of expending more energy. The same process occurs in childhood. Many factors have influenced this process. Increasing urbanization with reduced open areas for play, in addition to the modern trend of more sedentary pastimes, such as television and computer games, mean that children take significantly less exercise. All measures of health (apart from sports injuries) are improved by regular exercise; children who exercise are significantly more likely to become adults who take adequate exercise. In addition to the provision of unhealthy snacks schools in Hong Kong place too little emphasis on sport and exercise.

As family practitioners we have a duty to promote health. It is important that we use our position of influence in order to educate adults and children alike about the dangers of inactivity and poor diet. As doctors and parents we should encourage children to exercise and discourage schools from providing carbonated drinks machines and unhealthy snacks. We would be horrified if schools provided cigarette machines for our children, yet obesity and inactivity currently represent the single greatest threat to the long-term health of the children of Hong Kong.