North Americans are drowning in a sea of calories that could bring on heart disease as early as the end of the teen years, a U.S. obesity expert warns.

Dr. David Katz, an outspoken opponent of fast-food, told delegates at the Canadian Cardiovascular Congress that it is only a matter of time before obesity overtakes tobacco as the leading cause of premature and preventable death.

"Children growing up in the U.S. and soon Canada are the first cohort in modern memory looking at a shorter life expectancy than their parents because of epidemic obesity and diabetes," said Katz, director of medical studies in public health at Yale University's school of medicine.

He said the human body was built for a time when we were forced to hunt and gather our food. Now teenagers play video games or watch television in between going into the fridge.

"It is a sea of calories in which we are drowning," Katz said, comparing the modern human to polar bears in the desert, unable to adapt to their environment.

Some of his recommendations to parents and the government include:

• Teaching children about healthy versus unhealthy foods;
• Dismissing fad diets;
• Devising a simpler food labelling system; and
• Demanding schools outlaw the sale of junk foods.

Katz also said parents should not try to force their children to finish all the food on their plates. They should outlaw sayings such as: "Finish your food. There are starving children in China," he said.

In Canada, there has been increased debate about the amount of physical activity children are getting at school.

According to an Ipsos-Reid poll conducted in September for Today's Parent magazine, 91 per cent of Canadians think provincial governments should make it mandatory for students from kindergarten to Grade 12 to have 30 minutes of physical activity a day in school.

As well, 94 per cent agreed the number of overweight children in Canada is a serious health issue.

Alberta Learning Minister Lyle Oberg said in August he wants to see mandatory physical education mandatory within two years.