U.S. President Donald Trump had a normal score on a cognitive exam and is in excellent health, although he could benefit from a lower-fat diet and more exercise, the White House physician said on Tuesday.

"In summary, the president's overall health is excellent," Dr. Ronny Jackson told reporters. "He continues to enjoy the significant long-term cardiac and overall health benefits that come from a lifetime of abstinence from tobacco and alcohol."

The examination took place on Friday toward the end of a week in which Trump's mental fitness for the job had come under intense scrutiny after a controversial book, Fire and Fury: Inside the Trump White House, portrayed him as a childlike and mercurial.

Jackson said Trump had performed "exceedingly well" on a cognitive assessment, which the president had requested. "The president is mentally very sharp, very intact. ... He is fit for duty," Jackson said.

The doctor said he initially didn't plan to do a cognitive assessment, citing his own experiences and interaction with the president and clinical guidelines. But he complied when the president requested a cognitive test as part of the more than four-hour physical exam, which Jackson said involved around 12 consultants.

The cognitive test was the Montreal Cognitive Assessment, which looks for signs of dementia or Alzheimer's, an incurable, degenerative brain disease. Sample questions include asking the patient to draw a clock face, putting in all of the numbers and setting the clock hands to a specific time. The test does not assess psychiatric fitness.

Trump scored 30 out of 30 on the test, Jackson said.

"I think he will remain fit for duty for the remainder of this term and even for the remainder of another [four-year] term if he's elected."

Dr. Ronald Petersen, an Alzheimer's disease expert at the prestigious Mayo Clinic, said he could not comment specifically on the president's cognitive health. 

However, he did say that, in theory, a perfect score on the Montreal Cognitive Assessment does not necessarily rule out cognitive decline. It is just one measure in a clinical judgment, he said in an email.

Trump underwent the medical exam on Friday at Walter Reed National Medical Center.

Trump, 71, is known to enjoy high-fat foods like fried chicken, hamburgers and steak — and while he plays golf, he does not have a daily exercise routine, something Jackson said he'd like to see progress on. 

"He's more enthusiastic about the diet part than the exercise part, but we're going to do both," Jackson said, adding that he might enlist Trump's wife, Melania, to help. 

The navy doctor exhausted reporters' questions during an unusually lengthy hour-long session.

Jackson, who opened the news conference by mentioning that the president had consented to the release of medical information, told reporters that there was "absolutely not" any information held back at the request of the president.

With files from CBC News