There are studies, but very limited of course that show efficacy with the things you mentioned though. There's limited interest in it though because most of those things simply have no profit potential.
> There's limited interest in it though because most of those things simply have no profit potential
This is not true. There is a lot of interest in the Keto diet, it has been well-studied and has uses in treating epilepsy. The reason it's not prescribed more generally is because of those studies, which show it doesn't work. Not everything is a conspiracy.
Not much money for the medical industry if they recommend putting down the fork and spoon.
A cancer researcher could rely on charities, academic institutions, and government grants to fund experiments. There is a lot of cash available to cancer research. If the researcher shows a cheap and effective method to combat even a specific type of cancer, that researcher will get tenure, book deals, and fame. So that's a rich researcher.
Big pharma can be a cutthroat industry that prioritizes profit over public health. But they're not a shadowy cabal behind every bad thing in the world.