So this would not look at, for example, the Okinawan diet, which certainly consumes quite a bit of fish protein but also rice as a source of carbohydrate.
RE Okinawa and the "blue zones, it seems to be more wishful thinking / fantasy vs reality:
https://www.biorxiv.org/content/10.1101/704080v1
Supercentenarians and the oldest-old are concentrated into regions with no birth certificates and short lifespans
The observation of individuals attaining remarkable ages, and their concentration into geographic sub-regions or ‘blue zones’, has generated considerable scientific interest. Proposed drivers of remarkable longevity include high vegetable intake, strong social connections, and genetic markers. Here, we reveal new predictors of remarkable longevity and ‘supercentenarian’ status. In the United States, supercentenarian status is predicted by the absence of vital registration. The state-specific introduction of birth certificates is associated with a 69-82% fall in the number of supercentenarian records. In Italy, which has more uniform vital registration, remarkable longevity is instead predicted by low per capita incomes and a short life expectancy. Finally, the designated ‘blue zones’ of Sardinia, Okinawa, and Ikaria corresponded to regions with low incomes, low literacy, high crime rate and short life expectancy relative to their national average. As such, relative poverty and short lifespan constitute unexpected predictors of centenarian and supercentenarian status, and support a primary role of fraud and error in generating remarkable human age records.
I had some time to look at the paper. I have a background in applied statistics, but not related to health or bio-statistics, so I get their approach and it looks solid to me.
If true, and I think that in general their methods are probably sound, it shows the risks and dangers of basing conclusions upon
outliers (the "supercentinarians") as opposed to the general main body of data, in this case, that would be the general population of these "blue zones". I have a feeling (unproven) that what has been going on is that someone identified some regions of the world as having a lot of outliers to the longevity norms. The ever-cautious scientists said, "we need to study these regions and individuals more before we draw conclusions", but the people who are less scrupulous and make paid TV adverts for a living jumped ahead and made an industry out of promoting them, garnering a lot of flashy attention. This paper, if upheld, would fall into the the former category, the normal workload of validating the observations, as ever-cautious scientists would do. Not sexy but necessary.