According to the American Institute for Cancer Research, soft drink consumption in the USA has increased by 500 percent in the past five years. Today's children consistently choose soda over milk, juice or water, creating a two-fold problem where excess calories are consumed and vital nutrients are lacking. Very few children, or adults for that matter, adjust their daily calorie intake to accommodate the "empty" calories contained in soda.

Another critical problem is growing portion sizes. A recent study published in the Journal of the American Medical Association found that, between 1977 and 1998, the serving size of an average soft drink increased from 13 fluid ounces and 144 calories to nearly 20 fluid ounces and 193 calories.

The average cheeseburger also grew from 165g to 207g, adding an extra 136 calories. Considering that an extra 100 calories per day can translate to an extra 10 pounds a year, the increase in portion sizes can have a big impact on a child's weight.

Once upon a time, it was against federal regulations to sell soda in schools. These days, schools rely on the profits from vending machines to fund extra-curricular activities, such as chess clubs or debating societies. According to Emilia Askari in a 2002 report in the Detroit Free Press, it's not uncommon for a large high school to make as much as $2,000 per month from vending machines.

Askari's report states that the amount of milk purchased by school districts nationwide dropped by nearly 30 percent between 1985 and 1997, yet in the same period soda purchases increased by a whopping 1,100 percent.

Vending machines in schools pose a huge dilemma for children who are being educated about healthy eating, yet walk out of the classroom to face unhealthy choices.

There are, however, many instances where vending machines in schools have been a success. Some schools offer "dairy-only" vending machines that sell milk, cheese and yogurt. The Minnesota school district has 16 vending machines, 13 of which stock only water and 100% fruit or vegetable juice; two with sports drinks; and one with soda that has limited hours of sale. There is also a staggered price structure, with water least expensive and soda most expensive.

This tactic has proved very successful, with increased profits for the school district and less soda and more water consumed by students.

The average American child or adolescent watches up to three hours of TV every day. Another three hours on the computer or video game adds up to six hours of leisure time spent in sedentary activities.

And it can't be forgotten that while watching TV, children are exposed to 10,000 hours worth of food advertisements in a year - most of them for high-fat, high-calorie foods.

Reduced levels of physical activity are a major contributor to the obesity epidemic. The American Academy of Pediatrics urges parents to limit total screen time to no more than two hours per day, and instead encourage outdoor or physical activities.