How Junk Food Works

The history of junk food and fast food is wrapped up in the industrialization of America. Before the early 1800s, food was almost exclusively prepared in the home and made with minimally processed ingredients grown locally and harvested seasonally. That's not to say that people ate healthy and varied diets, but the very idea of junk food − highly processed, commercially manufactured snacks − didn't exist.

Andrew F. Smith, a food historian and author of "Fast Food and Junk Food: An Encyclopedia of What We Love to Eat", credits the industrialization of flour mills in the 1820s with the launch of the junk food era [source: Smith]. Innovations in milling technology and improvements in transportation brought inexpensive white flour to the masses. Even today, cheap white flour is the foundation of low-fiber, high-carbohydrate burger buns, cookies and snack cakes.

During the American Civil War (the 1860s), troops grew accustomed to eating from cans and jars of mass-produced rations. They came home craving the same convenience and familiar tastes. The rise of the industrial factory drew people away from farms and into the city. Food vendors parked their carts outside the factory gates, offering the first "fast foods" to hungry workers [source: Smith].

The first great American junk food was Cracker Jack, a salty-sweet blend of popcorn, molasses and peanuts introduced by brothers Frederick and Louis Rueckheim at the Chicago World's Fair in 1893 [source: Fernandez]. The recipe wasn't a novelty, but the Rueckheim brothers' true genius was marketing − a prize in every box! − and their trademark wax seal packaging. By 1916, Cracker Jack was the best-selling snack in the world [source: Smith].

The history of soft drinks goes all the way back to 17th-century Europe, where carbonated water was first mixed with lemon juice and honey for a bubbly sweet concoction [source: Korab]. In America, the first batches of Coca-Cola and Pepsi-Cola syrup were mixed at pharmacy counters in the 1880s and 1890s and sold as a refreshing, healthy elixir to aid digestion [sources: The Coca-Cola Company, Pepsi-Cola].

The emergence of fast food was fueled by the rise of automobile culture and the suburbanization of American cities in the 1950s [source: Smith]. Originally a convenient novelty, ordering a burger and fries at the "drive-thru" soon became an American institution.

The second half of the 20th century witnessed explosive growth in the variety, affordability and ubiquity of junk food and fast food. Innovations in manufacturing, packaging, transporting and marketing junk food − particularly to children − turned a rare treat into a steady diet for millions. And all the big companies employ an army of food scientists who know just how to get us coming back for more.

There's a reason why it's called a Happy Meal − junk food is extremely pleasurable. And that's not an accident. Junk food has been carefully engineered by food scientists and snack manufacturers to hit the "sweet spot" that keeps us wanting more, and more, and (gobble, gobble) more.

It starts in the mouth. One of the distinguishing characteristics of all great junk food is mouthfeel. Cheetos are famous − or infamous, depending who you ask −for delivering explosive cheesy flavor without the heavy, greasy mouthfeel of actual cheese. Instead of tasting like the salty fat bombs they are, Cheetos literally melt in your mouth.

One food scientist calls this vanishing caloric density [source: Moss]. Your brain relies partially on mouthfeel to determine how many calories are in a particular food. By melting into nothingness, Cheetos trick you into eating the whole bag.

Fast food cashes in on the same mouthfeel science. A meal of a hamburger and fries is undeniably fatty, and your mouth knows it. But food scientists have discovered that the potentially unpleasant mouthfeel of greasy fries is perfectly balanced out by the astringent quality of carbonated beverages [source: Cuda Kroen]. And bonus points for balancing salty with sweet!

The food industry spends tens of millions of dollars a year researching and developing the ideal combinations of mouthfeel and crunch that keep us coming back for more. Apparently there's a $40,000 artificial chewing device that calculates the exact amount of pressure required to devour a chip (the perfect crunch: 4 pounds per square inch) [source: Moss].

Junk food science also owes a lot of credit to evolutionary biology. The brains of modern humans evolved in a place and time when daily life was consumed by the search for more calories. As omnivores, we can physically digest a wide variety of foods, but not all foods are calorically equal. Meat, for example, delivers many more calories per bite than leaves.

To feed ourselves most efficiently, the brain evolved ways to quickly identify the most calorie-dense foods. And it still does, even though food scarcity is no longer an issue. When hunger strikes and we stand in the kitchen choosing between an apple and a bag of potato chips, a region of the brain called the ventromedial prefrontal cortex screams, "Chips, you fool! We could die tomorrow!" [source: Tedesco].

The overconsumption of junk food has been directly connected to higher rates of obesity and increased risks of heart disease, Type 2 diabetes and even depression.

A diet that's high in sugar, simple carbohydrates (white flour, potatoes, sugary drinks) and saturated fat is one of the chief causes of the obesity epidemic. More than one-third of American adults are obese, and kids are following the trend. An alarming 21 percent of adolescents 12 to 19 years old are obese, as are 18 percent of children 6 to 11 years old − double the obesity rates from the 1980s [sources: CDC, CDC].

What's the connection between Type 2 diabetes and junk food? Americans, on average, consume 22 teaspoons of sugar a day, much of it in the form of high-fructose corn syrup served up in soft drinks and candy bars [source: Boseley]. When the body breaks down these simple carbohydrates, blood sugar levels spike. That forces the pancreas to quickly release insulin so that cells can absorb and store those sugars. Frequent blood sugar spikes eventually wear out the body's insulin-producing cells, triggering Type 2 diabetes [source: Harvard School of Public Health].

Type 2 diabetes carries a host of health complications including heart disease, painful nerve damage, kidney damage, an increased risk of Alzheimer's, and foot infections that can require amputation [source: Mayo Clinic].

Even our mental health can be affected by a poor diet high in refined sugars, processed meats and high-fat dairy desserts. Researchers have found a strong connection between a junk food diet and higher rates of depression [source: Zeratsky]. High fat and sugar levels are known to increase inflammation and oxidative stress in the brain – which can disrupt the brain's chemical signaling [source: BBC News].

And what about junk food addiction? A growing body of research shows that obese adults and children exhibit classic signs of addiction − out-of-control binge eating, increased tolerance and withdrawal symptoms − that are usually associated with alcohol and drugs [source: Gray].

The U.S. federal government has tried to enact tougher regulation of junk food, particularly its marketing and availability to children. The U.S. Food and Drug Administration now requires restaurant chains and movie theaters to post calorie counts directly on their menus, and sugary soft drinks have been removed from most school vending machines [source: Tavernise and Strom].

Still, fast-food chains continue to spend billions of dollars marketing their high-calorie, low-nutrition foods to even the youngest children. In 2012, McDonald's alone spent 2.7 times as much money on advertising as all fruit, vegetable, bottled water and milk producers combined [source: UCONN Rudd Center for Food Policy & Obesity].