Definitely tongue in cheek. He has said how wrong he was being a vegetarian for the first 25 years, then Atkins, Paleo, then Keto for a hot minute, until he decided to find their one unifying theory, and so far Protein:Energy is holding up. But should something better come along, he will promote it. It is so refreshing to hear a doctor say he was wrong multiple times in an interview, and willing to change.