I want to know the answer to the following question:
In which year was there a cover article on the National Geographic regarding diet recommendations?
All the background I'm provided with is that "The article is a lifestyle survey of three populations, Sardinians, Okinawans, and Adventists, who generally display longevity and "suffer a fraction of the diseases that commonly kill people in other parts of the developed world, and enjoy more healthy years of life."". Is that enough to answer the question?