As Attawapiskat Chief Theresa Spence continues her hunger strike, a critical care doctor is warning that the human body begins to break down after such a long period without food.

Dr. Gwynne Jones hasn't treated or inspected Spence.

Chief Spence has been on a hunger strike for three weeks and is requesting a meeting with Prime Minister Stephen Harper over a number of issues, including treaty rights.

Dr. Jones told CBC's Ontario Today that it is helpful Chief Spence is consuming hot fish broth during the hunger strike, but doesn't believe that's enough to maintain good health

"It's happening simultaneously with the breaking down of muscle and lean body tissues that are fundamental to her energy production and to her immunity," he said.

As a health-care provider, Jones said it's difficult to watch.

But he said there isn't an ethical obligation to intervene even if her health deteriorates further, because it's her right to take this action.

"The only reason to intervene is if she wishes it," said Jones. "I think it's a tragedy that she's having to use her autonomy in this way."

Jones said after three weeks with no food, a person is "very vulnerable" to infections in the lungs and stomach, which can turn "rapidly fatal."