RTÉ's Washington Correspondent Brian O'Donovan looks ahead as US President Donald Trump is set to undergo his first medical examination since taking office.

Usually going for a medical check-up isn't a big deal, unless of course you're the President of the United States of America.

Later today, Donald Trump will undergo an examination at the Walter Reed Medical Center in Bethesda, Maryland, which is just outside Washington DC.

Here in the US, there is a lot of media interest in the president's health and Donald Trump was asked about his medical check-up by reporters yesterday.

He told them that he expects it to go well and that he would be surprised if it did not.

A smiling President Trump said: "It better go well, otherwise the stock market will not be happy."

The president's medical examination was announced last month after he slurred part of a speech in which he declared the United States recognised Jerusalem as the capital of Israel.

Michael Wolff, author of 'Fire and Fury: Inside the Trump White House,' has claimed that Donald Trump lacked the mental fitness to serve as president, describing him as an "undisciplined man-child" who did not want to win the election.

The claims drew an angry reaction from the president, his aides and supporters. Mr Trump took to Twitter to describe himself as "a very stable genius" and "like, really smart."

Today's physical examination is not expected to include a psychiatric evaluation.

Yesterday, White House spokeswoman Sarah Sanders told reporters the examination will be conducted by the presidential physician Ronnie Jackson.

A statement about the results will be released today, and, at the White House on Tuesday, Dr Jackson will give details on the president's health and take questions.

Past presidential examinations have included vitals such as height, weight, body mass index, resting heart rate, blood pressure and oxygen saturation in the blood.

They can also include more detailed examinations of the heart, lungs, vision, cholesterol and blood glucose that could point to problems.

So how healthy is Donald Trump?

During the 2016 presidential campaign, he published a letter from his long-term doctor Harold Bornstein that stated he was in "excellent physical health."

Mr Bornstein had previously written about Mr Trump's health in glowing terms, stating in 2015 he would be "the healthiest individual ever elected to the presidency." 

On the plus side, President Trump doesn't smoke and doesn't drink, a decision he says was influenced by his brother Fred. He was an alcoholic who died at the age of 43.

The president's doctor will no doubt welcome these facts but is likely to be quite concerned about his patient's eating habits.

According to a recent book Donald Trump is a big fan of fast food and soft drinks.

'Let Trump be Trump' was co-written by former Trump campaign manager Corey Lewandowski and claims dinner could be "two Big Macs, two Filet-O-Fish, and a chocolate malted (milkshake)".

The book states that on the campaign plane "there were four major food groups: McDonald's, Kentucky Fried Chicken, pizza and Diet Coke." The plane was also well stocked with biscuits, crisps and pretzels. 

If the reports are true, Donald Trump's doctor could have some stern words for the president when he carries out his check-up later today.