WASHINGTON – A White House doctor pronounced President Trump is medically fit to serve as commander-in-chief on Tuesday, adding that he easily passed a voluntary cognitive assessment designed to test his mental reflexes.

"The president's general health is excellent," Dr. Ronny Jackson told reporters during an unusual briefing at the White House, days after completing Trump's first physical as president.

Jackson said the 71-year-old, 239-pound president could use more exercise and a better diet that is lower in fat and carbohydrates. Trump, who is known to eat junk food and to avoid exercise beyond golf, is overweight. Jackson said they set a "reasonable goal" of losing 10 to 15 pounds next year and developing a regular exercise routine.

"He's more excited about the diet part than the exercise part," Jackson said.

Trump, who has gained three pounds since his physical exam in 2016, takes a drug to lower his cholesterol, and Jackson said he could increase the dose. The doctor added that Trump does not use tobacco or alcohol, one of the reasons why which is in good health in general.

The annual physical examination of the president at Walter Reed National Military Medical Center, which took place on Friday, is a regular practice. But the Trump exam has gained more scrutiny in the midst of questions about his mental state.

Jackson said he "initially had no intention" of including a mental fitness test of the president at his first annual physical exam, and noted that he had "absolutely no concern about his cognitive ability or neurological functions." Such exams are not usually part of the presidential physical exams.

Still, at the president's request, Jackson made an assessment to detect any cognitive impairment such as Alzheimer's, and Trump scored a perfect score.

"The president is mentally sharp," Jackson said.

Critics began to openly question Trump's mental state this month after a tweet in which he said he had a nuclear button larger than North Korean leader Kim Jong Un, and the publication of Fire and Fury a book about the White House, in which Trump's anonymous acquaintances questioned the president's mental stability.

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Asked how Trump could stay healthy with a diet that includes McDonald's and Diet Cokes, Jackson said: "It's called genetics, I do not know."

Jackson estimated that Trump only has 4 to 5 hours of sleep per night. "He does not sleep much," he said.

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