Nutrition epidemiology studies are not scientific experiments; they are wildly inaccurate, questionnaire-based guesses (hypotheses) about the possible connections between foods and diseases. This approach has been widely criticized as scientifically invalid [see here(1) and here(2)], yet continues to be used by influential researchers at prestigious institutions.
Even if you think epidemiological methods are sound, at best they can only generate hypotheses that then need to be tested in clinical trials. Instead, these hypotheses are often prematurely trumpeted to the public as implicit fact in the form of media headlines, dietary guidelines, and well-placed commission reports like this one.
Tragically, more than 80%(3) of these guesses are later proved wrong in clinical trials. With a failure rate this high, nutrition epidemiologists would be better off flipping a coin to decide which foods cause human disease.
Although, potentially interesting: Self reported mental well being is correlated with self reported belief of eating more fruits and vegetables. Though a much weaker claim than the headline, I think this is still useful information. Without looking at the study, you can't rule out that there was something about the surveys that caused this correlation, but if there wasn't, it certainly would be interesting to try to find out why this correlation exists.
Even if you think epidemiological methods are sound, at best they can only generate hypotheses that then need to be tested in clinical trials. Instead, these hypotheses are often prematurely trumpeted to the public as implicit fact in the form of media headlines, dietary guidelines, and well-placed commission reports like this one.
Tragically, more than 80%(3) of these guesses are later proved wrong in clinical trials. With a failure rate this high, nutrition epidemiologists would be better off flipping a coin to decide which foods cause human disease.
(1) https://www.frontiersin.org/articles/10.3389/fnut.2018.00105... (2) https://jamanetwork.com/journals/jama/fullarticle/2698337 (3) https://rss.onlinelibrary.wiley.com/doi/full/10.1111/j.1740-...
Ref: https://www.psychologytoday.com/us/blog/diagnosis-diet/20190...