If you are over 40 and wish to live a long, healthy, productive life, free of dementia, here are a few of the rules. Eat unenriched white rice, unenriched pasta and unenriched white bread — unenriched with iron, that is. Avoid Raisin Bran, Grape Nuts or other iron-enriched cereals. Avoid muffins, doughnuts, cookies, cakes etc. since they are almost always made with iron-enriched flour. And iron should be avoided by the elderly.

Drink coffee and black, green and jasmine tea (none should be decaffeinated), and red wine (in moderation). Reduce your intake of milk. And of course, eat more beans, fish and seafood. Include herring, sardines and anchovies, all in moderation. Consume less red meat and sugar, but increase consumption of fermented and pickled foods and dried fish. Add Swiss chard, spinach, chicory, kale, leaf lettuce, escarole and borage to your diet and flavor generously with basil, thyme, oregano and marjoram. Eat other vegetables and rustic, dense and chewy sourdough breads.

Enjoy non-sweet fruits, Reduce cheese and canola oil. And keep your weight down.

All this advice comes from Dr. Preston Estep 3rd, a Vineyard visitor this summer and director of gerontology at the Harvard Genome Project. In Japan, where fish and white, unenriched rice are the most important elements in the diet, and where there is little obesity, the average life span for men is 80; for women 87. In the United States, where the diet includes much more red meat, enriched cereals and breads, and where there is considerable obesity, the average lifespan for men is 78; for women 81 or 82.

Residents of France and Italy who live near the Mediterranean Sea and northeast of Madrid, Spain are also long-lived, according to Dr. Estep. The oldest person in Europe today is 117-year-old Emma Morano, who still lives alone in the Italian region of Piedmont and prepares her own meals — largely pasta and eggs, washed down with a little homemade brandy, he said in a recent interview.

But these Southern Europeans, he points out, also largely follow a diet with little red meat and plenty of unenriched carbohydrates.

This is all put forth in Dr. Estep’s book, The Mind Span Diet: Reduce Alzheimer’s Risk, Minimize Memory Loss, and Keep Your Brain Young. Dr. Estep and his wife, Jeanne Calment, were guests recently at Cynthia Riggs’s Cleaveland House in West Tisbury. There, to their delight, they discovered that their co-host, Ms. Riggs’s husband Dr. Howard R. Attebery, in the 1940s had also been interested in the food habits of the Japanese. He had been comparing incidences of colon cancer among Japanese who remained at home on a Japanese diet and Japanese who had moved to the United States. Dr. Attebery, who had retired from work in public health as a dentist for Santa Cruz and Sonoma Counties in California, was doing this under the auspices of the National Institutes of Health. His work involved studying bacteria in the large intestine of both groups.

Dr. Attebery was equally delighted to have Dr. Estep, 56, a fellow scientist who has a degree in genetics from the Harvard Medical School, as a guest at Cleaveland House with whom he could exchange views.

Now 94, Dr. Attebery, still of sound mind (he has been studying Island pond life since his arrival on the Vineyard in 2013) is in full agreement with Dr. Estep’s research. He too believes that what you eat plays an immensely important role in how long and how satisfactorily you live. Red meat is detrimental in one’s diet, both insist. Fish is good, Dr. Attebery agrees. Because he and his wife raise and befriend chickens and guinea hens, they are less likely to favor chicken as a substitute for red meat. (Dr. Estep does consume some poultry). But at Cleaveland House, if the Atteberys do eat chicken, it is never one of their own. Indeed, a favorite family pet is Friendly, a Plymouth Rock hen. She is best friends with Limpy, a guinea hen who had to have a leg amputated, and as a result of her strange gait is shunned by all guinea hens and chickens in the family flocks except Friendly.

Both birds have devoted admirers in their Cleaveland House proprietors — Friendly for comradeship and Limpy for spunk. While the two scientists sat outdoors talking on a recent day, Limpy and Friendly moved happily about, occasionally interrupting the erudite conversation with friendly pecks.

Agreeing with each other that iron-enriched flour poses a grave danger to clear-headed longevity, the two scientists noted that they were now both making their own bread, using unenriched flour.

For those who would like to pursue his dietary advice in the hopes of living a longer, clear-headed life, Dr. Estep ends his book with a section of healthy recipes. They include couscous and tabboleh salads, rice salad Nicoise, zucchini soup, roasted tomato and bean soup, fava bean and eggplant stew, stir fries and grilled salmon. There is even a recipe for sage-roasted chicken (with apologies to Friendly).

Although the Esteps left Cleaveland House at the end of July, they are continuing their summer holiday in Oak Bluffs this month.