[eyeundersand]

This was going to be my comment too. N = 20 is atrocious and that too only over 2 weeks. Think any significant, measurable changes to mental health outcomes would probably take a lot longer than that to manifest. I further find results from any kind of "food recall" surveys (or just surveys in general) hard to believe. Stated vs. revealed preferences/outcomes should be a bigger debate imo.

[mtrpcic]

Any major changes to gut biome will definitely take more than two weeks. Anyone who has ever had to do an elimination diet will tell you that it can take 4 to 6 weeks for things to normalize when making dietary changes.