US health secretary Robert F Kennedy jr says his boss President Donald Trump “eats really bad food”, especially when travelling.

Trump mainly eats junk food, Kennedy said on a podcast with Katie Miller.

He said the choice was mostly for security reasons but also because Trump trusts the products of large companies.

Kennedy said on the podcast released on Tuesday (US time) that Trump “doesn’t want to get sick when he’s on the road”.

“If you travel with him, you get this idea that he’s just pumping himself full of poison all day long and you don’t know how he’s walking around, much less being the most energetic person, you know, any of us have ever met,” he told Miller, who is the wife of Trump’s deputy chief of staff Stephen Miller.

Asked who had the most unusual eating habits, Kennedy said it was Trump.

“The interesting thing about the president is that he eats really bad food, which is McDonald’s, and, you know, candy and Diet Coke,” he said.

“He drinks the Diet Coke at all times.

“I don’t know how he’s alive, but he is.”

However, Kennedy said Trump “actually does eat pretty good food usually”, when at home at his Mar-a-Lago residence in Florida or the White House.

He described Trump as being in “incredible health,” and having “the constitution of a deity”.

-with AAP