Photograph by Sean Gallagher, Nat Geo Image Collection
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Walnuts for sale in a street market in Xining. Qinghai-Tibetan Plateau. China. 2011
Photograph by Sean Gallagher, Nat Geo Image Collection
The Plate

Walnuts Through Time: Brain Food, Poison, Money, Muse

The latest on the list of foods for boosting memory, concentration, and cognitive function may just be a handful of walnuts. A recent study published in the Journal of Nutrition, Health and Aging (and, to be fair, funded in part by the California Walnut Commission) found that walnut-eaters scored significantly better on a series of cognitive tests, variously measuring everything from reaction time to story recall. Researchers guess that this may be related to walnuts’ high content of antioxidants and omega-3 fatty acids, notably alpha-linolenic acid—versatile ingredients that may also have protective effects against cancers and cardiovascular disease.

Similarly, a 2014 study led by Abba Chauhan at the New York State Institute for Basic Research in Developmental Disabilities found that mice fed a walnut-supplemented diet had better memories, learning abilities, and motor coordination, and less anxiety than the walnut-deprived control mice —who, in comparison, were a forgetful, dim-witted, and stressed-out lot. Mice, of course, are a long way from people – but the hope is that such results may eventually help lead to a remedy for Alzheimer’s disease, an incurable condition that currently afflicts over five million Americans.

Science, when it comes to walnuts, is late to the party. Walnuts, for much of their long relationship with human beings, have been touted as brain food. According to the medieval Doctrine of Signatures, which ascribed therapeutic properties to plants based on their resemblance to specific parts of the human body, the crinkly kernels of the walnut —which do look creepily like brains—were a good bet for treating head wounds, headaches, mental illness, and epileptic fits.

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Black Walnuts, Jans nigra, growing on a tree in their protective and sticky coating. Photograph by Animals, Animals

Opposing theories held that walnuts, while certainly affecting the brain, weren’t doing it any good. The 1393 Le Menagier de Paris, for example—a collection of fashion tips, household hints, recipes, and etiquette strictures, written by an elderly husband for his teenage bride—avers that walnuts, rather than curing, actually cause headaches; and Pliny the Elder, in his first-century Natural History, warns that even sitting beneath a walnut tree brings on a “heaviness of the head,” since walnut leaves give off a poison that penetrates the brain.

This suggestively brain-like walnut is the nut that we know as the English walnut, the common walnut of fall supermarket bins. Scientifically known as Juglans regia, the English walnut most likely originated in Asia Minor. Both Greeks and Romans cultivated it; and walnuts were among the foods hastily abandoned on the table in Pompeii’s Temple of Isis on the fatal 24th of August in 79 when Mount Vesuvius blew its top.

The English walnut is also known as the French or the Persian walnut, both of which nicknames suit it better, since the English, initially, don’t seem to have appreciated it much. In 8th century France, Charlemagne ordered walnuts planted in his orchards; French church tithes could be paid in walnuts; and walnuts were considered desirable enough that French towns appointed official measurers of walnuts to protect walnut consumers from fraud. English enthusiasm, however, seems to have lagged. Food historian Waverley Root claims that walnuts—other than as a Victorian after-dinner accompaniment to the port and Stilton cheese—were essentially absent from British cuisine until after World War I.

European nut cookery got a jumpstart from the Crusades. The Crusaders, between bouts of butchery, were much taken with Arab foods and recipes. Among those that they brought home was the practice of making pastes of ground almonds and walnuts to be used as a basis for fish and meat sauces. One of the earliest known English recipes incorporating walnuts is for just such a sauce, intended to be served with “Stokfysshe:”

“Take curnylles of walnotys, and clouys of garleke, and piper, brede, and salt, and caste al in a morter; and grynde it small, & temper it up with the same brothe that the fysshe was sode in, and serue it forth.”

Most of America’s early English walnuts were imported from Spain and cultivated by monks in the California missions; today 99 percent of the U.S. walnut crop comes from California’s Sacramento and San Joaquin Valleys. In North America, however, English walnuts are not the only walnut game in town. Runner-up in commercial importance is the equally nutritious native black walnut, Juglans nigra.

Black walnuts aren’t everybody’s cup of tea. Their taste is far stronger than that of English walnuts, earthy, pungent, oily, and in your face. If black walnuts had a soundtrack, writes Indiana food editor Mike Petrucelli, it would be Darth Vader’s theme from Star Wars. Fans, on the other hand, ecstatically compare the taste to a mix of caramel and anise.

Chances are that our native walnut didn’t figure heavily in the native American diet because, delicious or not, black walnuts are next to impossible to crack. Walnuts fall from the tree encased in a thick green husk or hull. In the case of English walnuts, this husk spontaneously cracks open and is relatively easy to peel off. Black walnut husks, on the other hand, stick to the inner nut with the tenacity of superglue. Recommended methods for removing them involve sledge hammers and/or driving over them repeatedly with a pickup truck.

This is a messy process, made messier by the husk’s content of juglone, an organic compound that turns everything it touches an inky and irremovable black. It’s also poisonous, though not, despite Pliny the Elder’s awful warning, to people. Instead, it’s toxic to a wide range of plants, among them maples, birches, and pine trees, lilac and blueberry bushes, hydrangeas, rhododendrons, cabbages, peppers, tomatoes, eggplants, and potatoes. Walnuts don’t play well with others; and black walnuts are particularly unfriendly.

Walnuts may have reached China as early as 200 BCE, possibly from Kashmir. There they became popular toys in the Chinese imperial court, where it was believed that rotating a pair of walnuts in the palm of the hand —much like Captain Queeg with his ball bearings —stimulated the circulation of the blood.

In recent years, this 2000-year-old pastime has once more come into fashion. Walnuts are now seen as status symbols by wealthy Chinese collectors —and the bigger, the older, and the more symmetrically matched the walnuts, the more sought after they are. Such pairs of walnuts can sell for hundreds or thousands —even tens of thousands —of dollars; one particularly desirable duo on a walnut-trading website was listed at $31,000.

But I say we’d be better off eating them.