OTTAWA — Americans can find out the precise state of Barack Obama's colon, courtesy of the White House, which publicly releases the results of the U.S. president's check-ups.

But Canadians have no idea what type of cancer has ravaged the once-athletic physique of Opposition Leader Jack Layton and forced him to take a leave of absence.

Layton's shocking announcement Monday that he's fighting a second -- and evidently more serious -- bout with cancer raises questions about just how much the public is entitled to know about the state of a political leader's health.

Layton's inner circle maintains there's no obligation to disclose all the intimate details of a leader's personal medical files. Nor is there any history of that sort of transparency in Canada.

"I think public officials at all levels have a balancing act to provide the public relevant information as well as holding back information of a private nature or information that may be perceived by others as general medical advice," says Brad Lavigne, Layton's principal secretary.

Layton's aides maintain the NDP leader has been transparent about his health challenges and provided the public with all the information they need to know.

He publicly announced in February 2010 that he'd been diagnosed with prostate cancer. He has refused to divulge what treatment he's received but has periodically assured Canadians that he appears to be winning that particular fight.

Lavigne says Layton has been reluctant to reveal his treatment regimen in part because he didn't want other cancer sufferers to think "those treatments might be suitable for them."

"That's an issue for the individual and their doctor alone."

Shortly before the country was plunged into an election last March, Layton underwent surgery for a hip that fractured during a regular work-out. What caused the fracture has never been explained. His press secretary, Karl Belanger, says "no link has been formally established" between the cancer and the fracture "so (to say) we don't know is the truth."

Nor has Layton ever specified exactly how his hip was repaired, other than to vehemently deny his sister's assertion during the campaign that he'd had a hip replacement.

When a leader is asking for the power to run the country, he has an obligation to assure voters he's fit for the job, Layton's aides acknowledge. They maintain Layton, whose cane became a symbol of courage during the campaign, did that.

"Mr. Layton was as straightforward and transparent as a leader could be at the time of the campaign," says Belanger.

Kathleen Monk, Layton's communications director, notes that Layton was front and centre throughout the campaign and what people saw "was a very healthy and vigorous Mr. Layton, who at times both staff and journalists had trouble keeping up to in terms of schedule."

No one could have foretold that Layton would be hit by a new form of cancer less than two months after the election.

"I think the nature, sadly, of this disease is that it's changed," says Monk. "And that's why he announced yesterday his temporary leave. He admitted quite publicly yesterday that he's facing serious medical challenges."

Layton has not, however, divulged the form of cancer he is now battling, the treatment he's receiving or the prognosis.

"I think that Canadians respect his right to keep some things about his treatment private," says Monk.

For his part, Belanger says: "I'm going to go with Mr. Layton's prognosis, which is he hopes to return by Sept. 19 ... He's beaten the odds before and he'll do it again."

Layton is not the first Canadian politician to face health questions or to choose to withhold some details.

There were concerns about Prime Minister Stephen Harper's when he sought treatment for a chest cold at the Ottawa Hospital shortly after the Conservatives won the 2006 federal election.

Doctors gave Harper a prescription for antibiotics and let him go.

The prime minister has spoken in the House of Commons about his struggles with asthma. As opposition leader in 2002, Harper expressed concern about how the Kyoto Accord might impact his own health.

"We all have fairly serious concerns about the environment and about our health. In my personal case, we are talking about the contents of the atmosphere and I have been a lifelong sufferer from asthma," Harper said at the time.

"I am very concerned about my respiration and how this agreement will affect my respiration."

But unlike Obama, Harper does not make his medical records public. Canadians must take the prime minister's spokesman at his word that Harper is in good health.

Ex-Bloc Quebecois chief Lucien Bouchard had his left leg amputated in the mid-1990s after contracting the flesh-eating disease. He went on to become Quebec premier.

Former prime minister Jean Chretien had surgery to remove a benign nodule on his lung in 1991, two years before his Liberals went on to win the next federal election. Even as he was under the knife, Chretien's communications director, who'd been kept in the dark, was assuring reporters the Liberal leader was just fine.

Early last week, the NDP's Lavigne told The Canadian Press that Layton was on vacation with his family and that there was "nothing to report on health."

Yet it emerged Monday that Layton had begun experiencing some "stiffness and pain" toward the end of the parliamentary session in late June. He disappeared from public sight after July 3 and underwent a battery of tests.

He received the results last Wednesday and began the next day informing his senior staff of his decision to take a leave of absence. They spent the next few days plotting their communications strategy for Monday's news conference and ensuring an orderly interim leadership process.

Lavigne says now he "wasn't trying to mislead." He knew Layton had undergone medical tests but, until the results were received, there really was nothing to report. Like all members of Layton's close-knit inner circle, Lavigne had been hoping against hope that the results would be good news.

The "need-to-know" approach to Layton's health is in stark contrast to the American approach.

The White House posted the results of Obama's February 2010 medical exam on the Internet.

Now Americans know their president takes anti-inflammatory medication for chronic tendinitis in his left knee. They also know his doctor told him to eat better to lower his cholesterol and to kick his smoking habit.

And they even know the state of the First Colon.

"The president completed all age-appropriate screening tests, to include colorectal cancer screening. A CT-colonography was performed with normal results," Obama's doctor wrote.

Larry Altman is a medical columnist for the New York Times who has long pushed for presidents to open their medical records to the public. Now a fellow at the Woodrow Wilson International Center for Scholars in Washington, Altman has grilled every president from Ronald Reagan to George W. Bush on their health. Some were more forthcoming than others, but all eventually gave him the scoop.

"My personal belief is that there is no illness that disqualifies anyone from running for office," Altman says.

"The issue is that the public is entitled to know what it is and take it into consideration in voting for X or Y as a candidate. If the public chose to want to elect a dying person for office, that's the public's right, as long as the public knew the facts."

During the last presidential campaign, both Obama and Republican John McCain disclosed their medical records. McCain's campaign released close to 1,200 pages to show the then 71-year-old presidential hopeful, who had endured three bouts of skin cancer and was tortured as a prisoner in the Vietnam War, was fit for office.

Not all American political figures have been so open about their health.

Those closest to Woodrow Wilson went to great lengths to keep his fragile health quiet before and after he suffered a debilitating stroke in late 1919 that forced him into seclusion for the remainder of his presidency.

Most Americans did not know Franklin Delano Roosevelt was usually confined to a wheelchair after a bout with polio. Only a few known photographs exist of the president in a wheelchair. During public appearances he usually stood upright, supported by an aide or one of his sons.

Other presidents have proudly displayed their scars.

Lyndon B. Johnson famously pulled up his shirt to show the press corps angry red stitches on his sagging, middle-aged paunch after he had his gall bladder removed.

While he was in office, doctors twice operated on Ronald Reagan to remove polyps from his intestine. Later a type of skin cancer was removed from his nose. But it was only years after Reagan left office that doctors diagnosed him with Alzheimer's disease.