President Trump's much-touted physical and mental stamina is the product of "perfect genes," Treasury Secretary Steve Mnuchin said Friday.

"This guy's got more stamina than anybody I've ever met," Mnuchin told Axios executive editor Mike Allen. "I mean, I thought I was in good shape. I traveled with him all the time. I mean, it's unbelievable. He's constantly doing things."

Allen followed up on Mnuchin's claim, asking how Trump maintained his energy level with his well-known penchant for fast food and lack of exercise.

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"He's got perfect genes," Mnuchin responded.

"What do you mean by that?" Allen quipped.

"He's got perfect genes," Mnuchin continued. "He's got incredible energy, OK? And he's unbelievably healthy."

Trump, 70, has long boasted about his high energy level, stamina and physical health. During the campaign, Trump's doctor released a letter asserting Trump would be "the healthiest individual ever elected to the presidency."

Trump also appeared on "The Dr. Oz Show" in September to discuss the results of another letter from his doctor, which included details on the then-GOP nominee's weight, blood pressure and cholesterol levels.

The president frequently attacked his 2016 rival, former Democratic presidential nominee Hillary ClintonHillary Diane Rodham ClintonChris Murphy’s profile rises with gun tragedies DNC, RNC step up cyber protections Gun proposal picks up GOP support MORE, casting doubt on her "stamina" while arguing he could work nonstop as president.