Edit: And it seems they're trying to sell some ebook "nutrition" guide for $20 a copy. This is garbage.
That is, it's bad food that doing the harm. Eating good food might help, but the better question is: how much kale must you eat to break even from that can of soda?
Rarebirdinc.com "specializes in internet marketing, website design, e- commerce development, strategic marketing..."
Never trust "a study", especially without a specific citation. Here's the study in question.
FWIW, the study was partially funded by the California Walnut Commission. This doesn't mean the science is bad, but probably worth double-checking the methodology. I have no evidence that it's bad. I just don't trust any single study.
Did they just examine NES2 outcomes, or did they try dozens and publish the ones with significant effects? Did they control for income? Is this the only study of walnuts and cognitive outcomes, or have we done dozens--published or otherwise--and are just picking the one with an interesting/desirable outcome?
This isn't just the walnut study. The "Berries" section talks about "a study" (still no citaiton, but Google knows). Was this a study of berries, or a study of hundreds of foods and they published the one that had interesting outcomes?
We do this stuff wrong all the time. Here's a nice video about one Very Bad study that made the news lately. TL;DR: They looked at numerous outcomes from thousands of variables and published one that was statistically significant.
Relevant xkcd: https://m.xkcd.com/882/
-- Sci-hub is timing out for me when I try, but this is the URL: https://sci-hub.tw/10.1007/s12603-014-0569-2
 This one: https://www.ncbi.nlm.nih.gov/pubmed/22535616