Well it depends on how you define BS. Elimination diets are a proven thing, and can have a profound effect on your mind and body. Good quality meat is immensely nutritious, and easy on the gut. It's not hard to digest. The result of this is that people 'can' feel a lot better doing it.

People generally eat a lot of crap, crap that was sold as being healthy for decades. Bread, pasta, etc etc etc yadda yadda. If you go carnivore, you are obliged to stop.

The BS part could be that the carnivore part itself is the cure, now that I believe to be BS. I believe that the magic is happening because of what you're not eating way more than what you are eating on carnivore.