The basic cause of obesity among children and adolescents is the energy imbalance between the calories they consume and the calories they expend through activity. But the causes of the increase in the number of overweight and obese children and adolescents are different.

There are several reasons to explain the increase in obesity in China. Traditionally, the Chinese diet consisted mainly of cereals and vegetables, with a little meat. As a result, the fat and sugar intake of the Chinese people remained low for a long time. However, as the country experienced an explosive economic development, fatty and sugary foods became much more widely available.

Due to the general population's ignorance of what constitutes proper nutrition, their consumption of fatty and sugary foods has increased significantly in the last decades, and so have the problems associated with it. Because of past famines in the country, different types of food, particularly high-fat food, are now very attractive, while the consumption of cereals, fruits and vegetables has decreased.

Eating in fast food places, particularly franchises of US fast food chains such as McDonald's, Pizza Hut or Starbucks, where the food is particularly high in fats and sugar, has become very popular. Although food in these places is expensive by Chinese standards, they offer an atmosphere that many Chinese find attractive, particularly young business people.

The attraction of fast food is not going to disappear. Instead, a new trend is developing. It started in Hong Kong, where McDonald's restaurants offer what has been called "McWeddings" where they provide wedding receptions for young couples. McDonald's will open a total of 250 new restaurants this year and expects to have 2,000 restaurants across China by the end of 2013. China's fast-food industry is now the fifth-largest in the world.

Another important factor for the increase in obesity levels in the general population is inadequate physical activity as a result of the increased use of television, computers and other passive leisure activities. The lack of safe and adequate spaces for physical exercise, and increased car ownership have also led to drastically lower levels of physical activity.

To confront the problem, it is necessary to cultivate healthy eating practices and healthy lifestyles for children. It is also important to increase the public's understanding of good nutrition through the mass media and the creation of community-based education programs.

Several countries have been experimenting with the use of fiscal measures to limit the consumption of foods high in fat, sugar and salt. Higher taxes on unhealthy foods can help improve health by changing eating habits, while at the same time generating important revenues that can be used for prevention efforts. The challenge for policymakers is how to develop effective programs and policies aimed at preventing and controlling what is fast becoming a serious public health problem, while at the same time allowing the people to enjoy the benefits of the country's remarkable economic growth.

The author is a public health consultant for several UN agencies and international organizations.