Agreed, but I think the mechanism relates to different microbes. If there are two microbes in your gut, and type A requires a dose of high-calorie, low-fiber food coming down the pipe every day, and type B is not able to reproduce as fast as type A but is able to live on high-fiber food, this tells you two things:

type A cannot have been living in humans thousands of years ago, but type B might have

type A benefits from making your brain worse at choosing healthy foods, and type B does not

Which kind would you rather have in your gut?