An examination in fluidity of various oils at room temperatureNicolas Pollock / The Atlantic

Growing up in Brooklyn in the 1950s, Jon Krampner used to put peanut butter on his spaghetti. Like so many kids of the era, he smeared the Space-Age goo on most other edible things, too. It was an act of love, and also part of a nationwide defiance of wartime scarcities still vivid in the collective consciousness.

But like so many of his peers, Krampner kicked the habit after he gained weight later in life. He eats it now only as a matter of journalistic research (including what went into writing his exhaustive history of peanut butter, Creamy and Crunchy).

His passion has lately been revived among millennials and boomers alike, as the midcentury concoction has been reinvented and sold in a “natural” form. In grocery stores next to Skippy, Jif, and Peter Pan (known in the world of peanut butter as the “Big Three”), among others, are offered more expensive versions with lakes of peanut oil afloat on top.

So, should we buy them? Is this an invitation back to the peanut party? It feels like it.

But what does that mean—natural? There is little that’s natural in farming legumes and crushing them into a paste and putting them in a jar and shipping them all over the world and spreading them on bread. Nature doesn’t do that.

Or, what is nature? Is the peanut butter question the domain of chemists or philosophers?

The answer is somewhere in between, and the question of natural peanut butter is among the most widely relevant debates in the modern history of food. At the moment, in part because of peanut butter, the word “natural” may be the most influential claim on food labels. Americans spend $40 billion annually on food so labeled—more than on “organic,” a word that has a regulated, standardized definition. And when we buy products labelled natural, what is it we think we’re buying?

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Unlike most other foods, there is a legal definition of “peanut butter.” To use the name, a product must contain 90 percent peanuts. (Technically a person could sell a bag of peanuts and label it peanut butter, but, you know, why would you?) And while “natural” isn’t defined or regulated, peanut butter is one domain where the term means something predictable to most people: Natural peanut butter just contains peanuts (and usually salt).

This is the way peanut butter was understood in its earliest days—and it was actually defined as such by the Food and Drug Administration in 1940. At the time, foods weren’t required to bear labels that listed ingredients. So when peanut-butter manufacturers inquired with the agency about adding glycerin to keep the oil from separating to the top—a phenomenon that, even today, people describe to me as off-putting, unnatural—the agency responded that glycerin could be added, yes, but it would have to be duly announced on the peanut-butter container.

The FDA has no exact definition for what can be considered “natural.” So what does it mean when a food has this written on the label?

That was because, the FDA reasoned, people who buy peanut butter are not expecting glycerin: Peanut butter is “generally understood” to mean “a product consisting solely of ground roasted peanuts, with or without a small quantity of added salt.”

This definition, which seemed simple and obvious at the time, started a landslide of attempts at defining what foods are. What, exactly, can be added to or replaced in a food without changing its definition?

Defining parameters seemed like a reasonable task, and it would have been, had it not been for the torrent of postwar food technologies. What we weren’t making anew—Jell-O salads, SPAM, Tang, Twinkies, sprayable cheeses—we were making in better, brighter, everlasting forms.

And so came the embrace of ever cheaper, sweeter, gooier peanut butters.

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Ancient Incan people appear to have pulverized peanuts thousands of years before peanut butter was defined in an FDA office in 1940. By that time, modern peanut butter had been around for about 40 years. American farmers had taken up peanuts after the boll weevil devastated cotton cultivation at the turn of the century. In 1894, a snack-food maker in Saint Louis named George Bayle began producing and selling his new butter product. It took off after being featured in the 1904 World’s Fair in Bayle’s home city. By 1907, nationwide production was up to 34 million pounds.

The most interesting thing about writing a book on peanut butter, Kramper says in a peanut lecture, was discovering that peanut butter was not invented by George Washington Carver. While the man did take out a patent on a peanut-based cosmetic, his legacy is rather the result of the fact that Carver was a segregationist. He was lauded as an exemplar of submission by the white establishment, which inflated his biography. “He’s incredibly overrated,” says Krampner, noting that when Carver died, his home was the third ever to become a national monument, “but he didn’t deserve it.”

In either case, peanut butter was a delicacy of the American south, difficult to procure in the North as it didn’t travel well. More than the story of Carver or the World’s Fair, what really led to the widespread use of peanut butter was a chemical process called hydrogenation.

In 1923, Heinz became the first brand of peanut butter to add hydrogenated vegetable oils. They made the product last longer on the shelf, and spread on bread more smoothly. Like glycerin, hydrogenation solved the annoying problem of oil separation. The idea caught on. A few years later, a tin of Peter Pan (which was sold in tins, like most peanut butters, until the metal was needed for war) bragged in large font: “improved by hydrogenation.”

Fats are just chains of carbon, oxygen, and hydrogen. When all of the carbons are filled with hydrogens, that is a saturated fat. When the carbon binding sites aren’t full, that’s unsaturated. The process of hydrogenation (adding hydrogen molecules) raises the melting point of fat, allowing it to be a semi-solid at room temperature (instead of a liquid like olive oil). Bombard a liquid oil with hydrogen in a lab, and the unsaturated fats change shape and become trans fats—which are creamy even when sitting on shelves for years.

It was this process of hydrogenation that democratized peanut butter. The chemistry led to the industrialization of peanut-butter production, and the arrival of beloved forms of peanut butter in almost every household in America.

A 1959 survey found that some peanut butters, adding ever more hydrogenated oils, had reduced their peanut content dramatically. They added sugar, too. Jif was even marketed under the slogan, “You have to jump for Jif because it’s creamy good with a touch of honey.” The FDA analyzed said creaminess and found that it was the result of hydrogenated oil, and not a small amount: The product was only around 75 percent peanuts.

The agency felt the need to intervene on grounds that this was an adulteration issue—when people buy peanut butter, they should be getting a “pure” product. So ensued a 12-year battle to redo the once-simple 1940 definition of peanut butter. How much can you add to peanut butter before it’s no longer peanut butter?

The FDA proposed a standard of 95 percent peanuts, with the remaining five percent being “optional ingredients” (like salt, sugar, or hydrogenated or partially hydrogenated peanut oil). But that was confounded by the enormous commercial success of Jif, with its creaminess and honey (and Skippy and Peter Pan, which also increased their sugar and hydrogenated oil use). Consumers clearly loved these sweet, spreadable butters.

Ultimately the FDA compromised with manufacturers in 1971, settling on the threshold of 90 percent peanuts that persists today. It was put to the test during the low-fat craze of the 1990s, when the big three created “diet” peanut butters that contained less fat, and the FDA blocked the use of “peanut butter” on the label. Instead, the concoctions had to be called “spreads.”

The process of defining peanut butter was so arduous and expensive that the agency gave up on trying to do the same for other food standards. Under Richard Nixon, the FDA pivoted to focused on safety and transparency of ingredients on food labels. This allowed for innovation and creative interpretations, like mayonnaise. In 2015, the egg industry attacked the food-tech company Hampton Creek over its vegan product called “Just Mayo,” arguing that mayo is defined by the inclusion of eggs. The FDA allowed the name to stand.

The challenge of “natural” foods still looms large, though. The FDA is working to define “natural” at the moment, a period for public comments on the matter having closed in May after the agency received more than 5,000.

This follows a federal attempt at defining natural in 1974, when the Federal Trade Commission proposed that “natural” foods are “those with no artificial ingredients and only minimal processing.” The agency deliberated for nine years before giving up.

The FDA will likely have to do the same. Jean Jacques Rousseau endorsed natural foods in 1762, writing, “Our appetite is only excessive because we try to impose on it rules other than those of nature.” He was not alone in this “appeal to nature,” a long-standing logical fallacy in philosophy which overlooks the fact that nature produces some of the most toxic substances that exist. Snake venom is natural. Influenza and hurricanes are natural. Defining nature is one of the great challenges of philosophy, as writer Alan Levinovitz noted on NPR, and not one that we will suddenly solve.

And the more immediate question of which peanut butter to use remains.

Partially hydrogenated oils are bad for our hearts, yes. As is too much sugar. But in the amounts of peanut butter that most of us eat, it’s tough to know if it really matters—especially if it can be produced more cheaply and live longer on a shelf, which means less food waste and more egalitarian access to peanut butter.

As people have recently grown wary of the health effects of trans fats, some peanut butters have incorporated fully hydrogenated oils (essentially a synthetic saturated fat). Manufacturers have taken to blending these fully hydrogenated oils with liquid oils in a process called interesterification, yielding a product with the desirable gooeyness and stability of a partially hydrogenated oil. It’s not yet clear whether that’s good for our bodies.

Ultimately, the question of peanut-butter superiority is a question of what constitutes better? Do refrigeration and shelf life matter? Are we talking only about nourishing our own bodies, or about minimizing waste and feeding a planet? There’s also the matter of enjoyment, which I tend to overlook.

In any case, as with every question about food in a world of defined by unsustainable production, peanut butter transcends physiology.

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