When I saw articles/videos on the centenarians in Italy or Costa Rica, I noticed that they don't shy away from dairy products or grains. They usually prepare their own food themselves, and don't eat too much.

You should know that most of the claims of unusual proportions of very long life from these communities turned out to be bunk. Many researchers spent much more effort on present-day cultural and medical study than they did on discerning historical verification, and so got their numbers inflated by retroactively-produced proof of age in communities small and disconnected enough to not make this their priority a whole hundred years ago (Okinawa), or fraudulently-adjusted age in communities with enough lack of national oversight to enable community-wide retirement fraud (Sicily).

The "Blue Zone Diet(s)" is still probably better than the American Big Mac and Sugar Cup diet, but it's unclear if they're actually living longer than people on other potentially wholesome diets.

The Okinawa study had even bigger issues, most notably age misrepresentation linked to the loss of koseki registers during WW2, which were unreliable to begin with and were reconstructed from family testimony after the war. I remember reading that on the top of all the rest, elderly people there tended to make mistakes of a full 12 years when giving their age because they would base themselves on their year sign, which they were more familiar with than the new Western calendar.