Rogan announced to his 8.2 million Instagram followers he had adopted a 'strict' carnivore diet - consisting of 'meat and eggs' - for the entire month.
Meanwhile, a record-breaking 350,000 have signed up for Veganuary: the world's biggest month-long pledge to eat plant-based throughout January.
"I'm getting my bloodwork done on Monday and then again when I'm done with the diet but I've been on it now for about five days and I'm already looking leaner," Rogan wrote.
"My energy level has been excellent too. Kind of shockingly good. I'm making sure this isn't a temporary placebo effect but at least for now I'm definitely experiencing some benefits."
The announcement was met with controversy, with many pointing out how Rogan branded James Wilks, Producer* of The Game Changers, 'fantastic' after he refuted some of the film's criticisms.
Rogan also said he was considering removing the episode in which paleo advocate Chris Kresser criticized the documentary.
"I guess James Wilks didn't make as big of an impression on you as I thought!? If you really want to lean out and feel healthy AF, you should try going plant-based for 30 days!" one user wrote.
"You'll destroy your competition! Your body will thank you! So will the planet and so will the animals."
*James Wilks co-produced The Game Changers with Joseph Pace, who was also a writer on the film.