President Trump Thinks Soda Kills Cancer Cells, Dr. Oz Says

President Trump is convinced drinking soda kills cancer cells in the body because pouring soda on grass kills the grass ... at least according to Dr. Oz.

Trump's Centers for Medicare & Medicaid Services Administrator was on a podcast with his boss' son, Donald Trump Jr., when the topic shifted to the Prez's love for Diet Coke.

Dr. Oz says Trump makes a point to drink Diet Coke and eat candy in front of him and Health and Human Services Secretary Robert F. Kennedy Jr. ... and tell them why the junk food is anything but.

As Oz tells it, Trump argues diet soda is good for him because if the carbonated drink kills grass, it must kill cancer cells too.

Dr. Oz says Trump isn't just drinking Diet Coke on the job ... he's also guzzling orange Fanta ... and Trump's kid backs him up.

Thing is ... Oz says Trump told him Fanta isn't unhealthy either because it's "fresh squeezed."

Trump's got a red button on his desk to order Diet Coke, and just yesterday he had McDonald's ordered to the White House.