More than one-third of Canadian children are overweight and about half of those obese, a trend that could leave kids exposed to diabetes and coronary disease later in life, Statistics Canada said Friday.

About 34 per cent of children aged two to 11 studied in StatsCan's National Longitudinal Survey of Children and Youth were found to be overweight between 1994 to 1995. Four years later, that figure had jumped to 37 per cent.

About half of the overweight kids were considered obese and the number is increasing, StatsCan said.Boys are slightly more likely to be overweight than girls.

While the study did not draw firm conclusions as to why Canadian kids are so heavy, it said poverty and a lack of exercise were possible factors.

"In recent years, childhood obesity and low levels of activity have emerged as important issues facing Canadian children," StatsCan said.

About 25 per cent of children with incomes below the "low-income cut-off" (LICO) were obese. For kids above that level, the rate dips to 16 per cent. There is no dollar figure for the low income cut-off; StatsCan refers to people with incomes below that level as living in "straitened circumstances."

"The proportion of overweight and obese children decreased as the family income increased," StatsCan said.

Perhaps not surprisingly, a lack of activity also plays a big part. Children aged four to 11 years whose weight was classified as normal and overweight had similar activity levels. But obese children did not.

"Obese children's overall activity levels were considerably different from the other two groups of children," the agency said.

Active kids are those who spend four or more times a week involved in activities such sports, dance classes, or outdoor exercise such as bicycling. Kids who do not take part in such activity at least once a week are considered inactive.

But the problem may be more serious than StatsCan figures show.

A study by the Canadian Fitness and Lifestyle Research Institute released in April showed that 55 per cent of children aged five to 17 were not physically fit, putting them at risk later in life for heart disease, stroke and diabetes.

Another poll by the Canadian Pediatrics Society found that 63 per cent of parents know their children are not fit, but blame homework, television and the Internet for their weight problem.

A major concern regarding childhood obesity is the long-held belief that obese children tend to become obese adults. However, StatsCan's longitudinal survey suggests that as children age, some may actually shed some of the extra pounds.

In 1994-95, 32 per cent of the children between two to 11 were overweight. Four years later when the same group was age six to 15, that was down to 28 per cent.

Obesity in adults is linked to greater health risks, heart disease, cancer, arthritis and Type-2 diabetes.

A 1999 study published by the Canadian Medical Association Journal estimated that in 1997, the total direct cost of obesity was more than $1.8 billion, or 2.4 per cent of total health care expenditures for all diseases. The World Health Organization has predicted that obesity could have as great an impact on health as smoking.

StatsCan measures obesity using the body mass index (BMI), which is based on both an individual's weight and height. To figure out your BMI, divide your weight in kilograms by your height in metres squared.

International cut-offs for children were used to classify children as overweight or obese. The child cut-offs are age- and gender-specific for children aged 2 to 20. For example, a boy aged 12 who was 1.1 metres tall, would be considered obese if he weighed 32.5 kg or more.