I’m pretty sure the Greek and Japanese longest living people were achieving their age less through diet and more through pension fraud. They live as long as equally wealthy places if they were born after good birth records started being kept
The Polynesians have sugar cane which has caused them health problems since before they had access to processed food, Japan is too far north for sugar cane.
Bad measurements, cases contrary to the researcher’s point were excluded, the biggest factor in places with too many people over age 100 was pension fraud - 40 year olds claimed to be 60 to get a pension, 40 years later they’re 80 year olds pretending to be 100