To understand how the military transformed American eating let’s first consider an event from November 1942. The United States has entered the war, and U.S. troops are attacking Vichy French forces along the Moroccan coast. Each fighter carries a backpack into which he has stuffed clothing, ammunition, and other gear, including two large cylindrical canisters weighing five pounds apiece. The canisters are loaded with tins of meat and beans, as well as bread, sugar, and other provisions that can keep a soldier fed for two days. But they also make the fighters’ already hefty loads even more so. As the men wade to shore and the backpacks become soaked, several are pulled underwater by the weight and drown, writes historian Lizzie Collingham in her book Taste of War.

It’s a startling reminder of the challenges armies face when feeding troops in the field. Each day troops require 4,000 to 6,000 calories, which they must procure on location or bring along. This predicament has long made armies interested in technologies that can make food, at the very minimum, portable and durable.

In fact, the cans the troops tote in Morocco are the direct descendants of a military innovation dating to the late 18th century, when the French government offered 12,000 francs to whoever could develop a method of preservation beyond the traditional smoking, drying, and salting to create foods the French army could take on wartime missions.

A confectioner near Paris named Nicolas Appert accepts the challenge. It will take several more decades before Louis Pasteur proves microorganisms make foods go bad. But through 14 years of trial and error, Appert discovers that by cramming foodstuffs into cork-sealed glass containers, then boiling them in water, he can keep the contents from spoiling. He collects his prize in 1810, and shortly thereafter, tin-plated iron replaces his original glass jars, and “canning” sweeps across Europe and the United States.

For the next 130 years, that’s pretty much where things stand. Around the world, armies send fighters to battlefields with rations that contain mostly hardtack or some other baked-to-a-brick biscuit, supplemented by canned foods, particularly meat. It’s a diet so lacking in fiber and nutrients that eating it for more than a few days causes constipation so severe that laxatives barely touch it. British World War II troops stationed in Northern Africa joke that the only thing that reliably moves their bowels is the German bombings, writes Collingham. Worse still are the vitamin deficiencies that such a limited diet can cause and that make the troops vulnerable to ailments ranging from ulcers, to skin lesions, to nerve inflammation.

When the United States enters World War II, the Quartermaster Corps, the office charged with supplying soldiers, has a staff of three and $300 to address the problems with combat rations. These numbers soon balloon, as historian Deborah Fitzgerald describes:

“Like the better-known Manhattan Project, the food provisioning work was likewise invisible to the citizenry, shuttered away in a diffuse but massive collection of university labs, packing plants, canneries, packaging companies, fruit farms, and hatcheries,” Fitzgerald continues. By the time the war ends, these collaborations introduce new food processing techniques and products to the market “at a rapid clip.”

Military-funded research spawns dry yeast (to make it easier to bake bread in military camps) and frozen concentrated orange juice (developed to supply troops with vitamin C). Military-sponsored scientists also refine cake mixes and improve a method to dry cheese and grind it into an easy-to-ship powder. After the war, this dehydrated cheese will inspire the Frito Company to mix the powder with cornmeal for a snack it dubs “Cheetos.” Foods flavored with dehydrated cheese flood the market soon after.

The military also experiments with a nutritional emergency bar made from chocolate, oats, and other ingredients that it contracts out to companies such as Hershey and that foreshadows today’s energy bars. When the military flies its troops to battle arenas, it serves them frozen, pre-cooked meals in reheatable, compartmentalized trays that are soon mimicked by frozen poultry giant Swanson, which rolls out the TV Dinner in 1953.

By sheer size the U.S. military shapes the food market. Sixteen million troops serve in World War II. The military doesn’t develop Spam, but it ships so much of the canned pork to its forces that in places with a large military presence, such as Hawaii, it becomes a staple in civilian cooking, too. And when a man named Forrest Mars patents a chocolate candy in 1941 that is meltproof thanks to a sugary shell, the military adds it to its battle rations; when the fighting is over, millions of troops return home with a taste for what become M&M’s.

“In many respects, the soldiers and sailors who ate [commercial food manufacturers’] products provided a diverse test market, and feedback was used to refine and improve their merchandise,” writes Gerry Darsch, director of the Department of Defense Combat Feeding Program, in 2009.

After the war ends in 1945, these partnerships continue. Researchers collaborate with the armed forces to improve methods for keeping bread from going stale. Today, almost all supermarket loaves contain enzymes that break down strands of starch that would otherwise harden the crumb.

In the 1950s the military encourages the food industry to repurpose a World War II technique used to transport blood plasma to battlefields by first freeze-drying it, then reconstituting it with water. Applied to foods, the method creates lightweight meals that last a long time. And while the chili con carne and other entrées produced for combat rations don’t win too many fans among troops, the freeze-dried fruit added to civilian cereals does. In the 1960s the military starts developing flexible packaging made from bonded layers of plastic polymers, aluminum foil, and other materials that are strong enough to securely seal food but lighter than the cans that so burdened the Morocco-bound troops. The resulting pouches now hold everything from individual portions of salad dressings to tuna on supermarket shelves.

It’s the military’s single-mindedness that has made it such an “outsized influence” on food technology, says Anastacia Marx de Salcedo, who explores many of these examples in Combat-Ready Kitchen: How the U.S. Military Shapes the Way You Eat. The military “will identify a set of objectives, then keep working toward that, going past failures and things that are not very promising, which in the private marketplace you may not want to do.”

Take, for example, shelf-stable guacamole.

The process behind it arises from the dilemma inherent in all military foods. They need to be many things at once—portable and nonperishable, but also nutritious and appetizing enough that troops will actually eat them. Current U.S. combat rations, called MREs (meals, ready-to-eat), must be shelf-stable for three years without refrigeration.

For a while, the military tries solving the quandary with irradiation. Pulses of high-energy gamma rays effectively kill microorganisms by ripping apart their molecular chemical bonds without changing the flavor or texture of food all that much. In the 1950s, the military starts spending what will become more than $50 million developing this method. In 1956 the Quartermaster Corps even presents an “all atomic” spread to Congress, which includes a month-old shrimp cocktail, 9-month-old fried chicken, and 10-month-old green beans—all theoretically safe to eat thanks to having been irradiated, writes historian Hannah LeBlanc.

However, the lawmakers are not allowed to consume the food since the Food and Drug Administration has not yet approved food irradiation. Americans are alarmed by media reports that foodstuffs are being treated with the same forces that make atomic bombs deadly, and the FDA requires test after test to ensure these foods are harmless. The agency cannot seem to make up its mind. In 1963 it grants the military its request to irradiate canned bacon, then revokes this decision a few years later. By the time the FDA finally starts approving irradiation in earnest in the 1980s, the army has mostly moved on to other methods of food preservation.

Specifically, key researchers from the irradiation project pivot to tinkering with pressure as a way to preserve food—really high pressure, higher than having an elephant balance on a stiletto heel.

If you apply that much compression force to food from all sides simultaneously, it can burst the cell membranes of microorganisms, such as molds and bacteria, while leaving the chemical bonds of proteins and fibers intact. This means a food stays basically unaltered. If a fruit was raw before, it is technically still raw but has now been sterilized. If put into a sterilized container, it can last for weeks, possibly months, without the need for chemical preservatives or other treatments.

The principle has been known since the late 1800s, but until the late 20th century, food processors pay little attention to it nor show any interest in developing the robust vessels and pumps necessary for that kind of pressure. However, other industries have, among them the producers of artificial diamonds and the manufacturers of blades for jet engine turbines, which are formed by compressing powdered metals until they fuse.

When Daniel Farkas, a food scientist who has shifted from irradiation to pressure, approaches such a company, the engineers have “a good laugh about squeezing tomatoes in one of their presses.” With colleagues, Farkas borrows a high-pressure unit and begins to systematically test how much pressure is needed to kill bacteria, molds, and other food-spoiling microbes. In 1989 the U.S. Army, ever on the lookout for methods to create more appealing combat rations, starts supporting such studies into high-pressure processing (HPP) and later awards contracts to companies to develop equipment for it. A firm called Elmhurst Systems repurposes used 155mm army field guns to build an early model of a food-treatment pressure vessel.

It turns out there needs to be water in the food for HPP to work effectively. That rules out dry foods, such as spices, which compact under high pressure while microbes are left mostly unharmed. Porous food with air pockets, including cakes but also strawberries and some vegetables, are also tricky since the pressure makes them collapse. But liquids or firm foods with sufficient moisture can be effectively cleared of bacteria using pressure, although bacterial spores often survive, which is why many HPP foods need to be refrigerated unless they are acidic enough to prevent bacterial regrowth. An HPP-treated smoothie lasts close to a month instead of three days; a brick of cream cheese almost half a year.

“The use of high hydrostatic pressure to preserve foods is the first truly new method for food preservation since Nicolas Appert developed the use of heat to preserve foods in sealed glass bottles some 200 years ago,” writes Farkas.

For the army, this means it can add dishes such as stewed apples to its MREs without having to cook them to mush to kill bacteria. As the HPP method gets perfected, U.S. civilian food producers jump on board. The first, in the mid-1990s, is Don Bowden, an owner of several Mexican restaurants in Texas, who has been looking for ways to provide his customers with more and better guacamole. Avocados are still mostly a seasonal product at this point, and guacamole is a regional dish. It browns too quickly to be transported or stored for long and is susceptible to Salmonella and Listeria contamination. Bowden has tried preserving guacamole with heat and citric acid, but both methods fundamentally change the dip.

With HPP, guacamole retains its silky texture, yet stays fresh for up to three months. Sealed in plastic it can be trucked into the furthest corners of the country—as can pre-peeled and diced avocados for restaurant use. Bowden starts selling his Wholly Guacamole in supermarkets, and consumption in the United States soars. In 2019, the last full year for which reliable numbers are available, U.S. consumers eat about 250 million pounds of processed avocado. Including fresh avocado, every U.S. resident consumes, on average, close to nine pounds of the fruit per year.  

Although HPP is relatively expensive—a single machine can cost up to $4 million—other products soon follow: salsas, baby food, and soups, which entice buyers with their promise of no chemical additives nor preservatives, as well as salamis and lunch meats, whose fats would melt with heat sterilization but which can be cold-pasteurized using pressure.

But if World War II and its aftermath change what Americans eat by setting off, in de Salcedo’s words, a “big bang” of food processing that leads to an ever-expanding universe of convenient, time-saving, and ready-to-eat foods, it also puts in motion fundamental changes in how the country thinks about what it eats.

The pressing issue for the doctors, dietitians, farmers, and food manufacturers gathered at the Mayflower Hotel in 1941 is the state of nutrition in the United States.

Nutritionists at the time know that foods are made up of proteins, carbohydrates, and fats and that vitamins and trace minerals are vital for maintaining health, although the why is often still unclear. And it’s becoming apparent that many Americans are not getting enough of these nutrients to keep them strong, especially compared with their enemies in Nazi Germany.

Bread is a main culprit, the experts decide. Most Germans eat a hearty bread baked from rye. Americans, on the other hand, like their bread soft and white, made from wheat that is roller-ground, which removes the harsh bran, but also the wheat germ, starving the staple of vitamins and minerals.

The experts decide that henceforth flour sold in the U.S. should be “enriched”—nutrients such as iron and B vitamins should be added back artificially. The military supports this guidance by proclaiming in 1942 that it will purchase only enriched flour. In 1943 President Roosevelt even signs an executive order that effectively makes flour enrichment mandatory. While this edict expires after the war, enriched flour is still common today.

And for the first time in history, the conference’s experts announce the specific amounts of protein, calcium, and iron as well as certain vitamins and other nutrients every American needs to eat daily to stay healthy.

This seemingly small step sets off a seismic shift. Following the publication of the first Recommended Dietary Allowances, Americans begin to look with new eyes at what they eat. Food becomes something that is seen, above all, as a vehicle for compounds that can either promote or inhibit health, writes Collingham in Taste of War. In the 1960s many Americans begin fearing saturated fat; in the 1980s they fall in love with omega-3 fatty acids; sometime before the turn of the millennium, carbs become public enemy number one, accompanied by a persistent hunt for the next “superfood,” be it blueberries, kimchi, or leafy greens.

In the decades after World War II and going on until today, the military researches how nutrition can help troops cope better with stress, lack of sleep, and the physical exertion of combat. Can electrolyte-spiked drinks protect against muscle soreness? Will fatty acids improve cognitive performance? Today, up to three out of four military personnel report that they are on regular supplements or nutraceuticals; one out of every five consumes at least three different kinds.

The shelves in civilian supermarkets also start brimming with products promising an extra nutritional boost. Iron gets added to baby food around the 1960s, folic acid shows up in cereals in the 1990s, and calcium becomes a mainstay in orange juice in the 1980s—and even appears, for a brief trial run, in Coca-Cola’s Tab soft drink.

Enriched, frozen, dehydrated, canned, powdered, pasteurized—almost all foodstuffs in supermarkets are processed one way or another these days. It is estimated that about 73% of the items in the U.S. food supply are now highly or ultra-processed.

These foods come with many advantages. Being shelf-stable, easy to prepare, and almost universally appealing—all vital for feeding troops—they have also given consumers access to a wider variety of eats with a generally high level of food safety. And their convenience has made the task of feeding a family less time-consuming than, say, in 1942, when the average U.S. woman, burdened by war conservation and preservation campaigns, spent close to 30 hours a week on food-related tasks, according to historian LeBlanc.

But highly processed foods also face mounting scrutiny for their role in rising obesity rates. These affect the military, too. Still struggling to find enough battle-ready personnel, last year alone the military rejected 52,000 potential recruits for being too heavy. And compared to a decade ago, the rate of active-duty service members classified as obese has more than doubled, with one in five now included in this category.

“Perversely, [the] view of food as solely the sum of nutrients also allows us, or rather food scientists, to declare highly processed foods healthy,” writes Collingham. “A conglomeration of hydrogenated oils, guar gum and corn starch masquerading as yoghurt, can be defined as healthy as it is low in fat and high in calcium.”

Processed foods also tend to have a comparatively high carbon footprint. It used to be that guacamole could be enjoyed only in areas where avocados grow. Now, ready-made guacamole is available everywhere year-round, processed by machines that build up a pressure higher than in the deepest parts of the oceans, packaged in plastics and foils that create waste, and trucked for thousands of miles, refrigerated all the way.

Recently, the armed forces have made sustainability a focus. BioMADE, a public-private partnership established by the U.S. Department of Defense, issued a call for proposals in 2022 for “innovations in food production that reduce the CO₂ footprint,” such as lab-grown meat or using agricultural byproducts such as almond shells to grow a fungus with potential as a meat alternative.

But the military food labs, located in Natick, Massachusetts, also still work on foods with ever-better shelf life, flavor, and texture. Just recently, researchers there perfected an evergreen request from troops: a pizza that stays shelf-stable for three years.

One of the latest technologies being explored for battle rations involves putting foods into a vacuum chamber (to lower the boiling point of water), then using microwaves to dry out much of its moisture, leaving a compact, dry, but still pliable piece of banana or cheesecake that tastes similar to the fresh thing but can last for years without refrigeration.

Another method uses ultrasonic waves—basically a high-energy form of sound—to “weld” together ingredients. This means that a manufacturer of, say, a granola bar can use sonic waves to compress the bar’s grains and fruits, forgoing the need to add sugar syrups as a binder.

The first examples of these products have already entered the civilian markets.

Support for this article is provided by The Pew Center for Arts & Heritage as part of the Science History Institute’s latest exhibition, Lunchtime: The History of Science on the School Food Tray.