The high rate of colorectal cancer in the Northwest Territories has prompted health officials to start a new screening program for early diagnosis.

The territory's rate for colorectal cancer, which begins in the colon, is 50 per cent higher than the national average for men and 67 per cent higher for women.

The rates are particularly high in Fort Smith, the Dehcho region and the Beaufort Delta.

Stantan Territorial Health Authority internist Dr. John Morse, who is leading the screening program, said the authority needs to understand what is causing the high rates.

"I'm trying to connect the dots," he said, adding dietary changes may be part of the problem for aboriginal people.

"I'm suggesting it's a change in the types of fat they're eating, and it's the fat you get in store-bought foods," he said.

Testing began in the Dehcho in November with plans to begin the screening program in Fort Smith next week and the Beaufort Delta later this year.

People between 50 and 75 are encouraged to take the test, he said.

The initial screening involves testing stool samples for blood content because that may indicate a growth in the colon, he said.

The more advanced screening involves a colonoscopy, he said.

Both tests can be done at the region's health centres.

If colorectal cancer is diagnosed and treated early, the five-year survival rate is 90 per cent, he said.