The Science Behind Junk Food

Few indulgences rival the sheer delight of a Snickers bar. Notice how your tongue tingles and your mouth waters even before you finish unwrapping it. That first bite is a euphoric wave of sweetness, saltiness, richness, and creaminess, igniting your brain's pleasure centers like a neon-lit cityscape. And the only way to sustain that joy? Take another bite.

Junk food is a triumph of culinary innovation. Unlike anything found in nature—imagine a Twinkie tree in your backyard—it’s meticulously crafted to deliver unmatched satisfaction through perfect blends of fat, sugar, and salt. Beyond its irresistible taste, junk food is affordable, convenient, and ubiquitous, found in fast-food joints, supermarkets, gas stations, truck stops, cinemas, and vending machines across America—and increasingly, worldwide.

The issue with junk food is simple: it’s devoid of nutrition. By definition, junk food offers minimal to no nutritional benefits while packing excessive calories from fat, sugar, and salt. This category typically includes candy, salty snacks, high-fat dairy products, packaged desserts, baked goods, and sugary sodas.

Junk food is often referred to as 'empty calories,' flooding our bodies with surplus energy—mostly stored as fat—while lacking essential dietary fiber, vitamins, and minerals necessary for healthy growth and disease prevention.

Is fast food synonymous with junk food? Not always. For instance, a Big Mac offers 24 grams of protein, 3 grams of dietary fiber, and 25% of your daily calcium needs. Yet, with 530 calories, it also contains 48% of your daily saturated fat and 40% of your sodium intake [source: McDonald's]. Add a large fries and a Coke, and it’s clear why most fast food is considered junk food.

Who first uncovered our love for these artificial delights?

History of Junk Food

The evolution of junk food and fast food is deeply tied to America's industrial revolution. Before the 1800s, meals were primarily homemade using locally sourced, seasonal ingredients. While diets weren't always diverse or nutritious, the concept of junk food—highly processed, mass-produced snacks—was nonexistent.

Andrew F. Smith, a renowned food historian and author of "Fast Food and Junk Food: An Encyclopedia of What We Love to Eat," traces the junk food era back to the 1820s, when flour mills became industrialized [source: Smith]. Advances in milling and transportation made white flour affordable, paving the way for low-fiber, high-carb staples like burger buns, cookies, and snack cakes.

During the American Civil War in the 1860s, soldiers grew accustomed to canned and jarred rations. Returning home, they sought the same convenience and flavors. As factories drew people to cities, food vendors set up carts outside factory gates, introducing the earliest forms of "fast foods" to busy workers [source: Smith].

Cracker Jack, the pioneering American junk food, debuted as a delightful mix of popcorn, molasses, and peanuts at the 1893 Chicago World's Fair, thanks to brothers Frederick and Louis Rueckheim [source: Fernandez]. While the recipe wasn't new, their marketing brilliance—like including a prize in every box and using wax-sealed packaging—made it a global sensation. By 1916, Cracker Jack was the world's top-selling snack [source: Smith].

Soft drinks trace their origins to 17th-century Europe, where carbonated water was first blended with lemon juice and honey for a fizzy, sweet drink [source: Korab]. In the U.S., Coca-Cola and Pepsi-Cola emerged in the 1880s and 1890s as pharmacy-counter remedies, marketed as digestive aids and refreshing tonics [sources: The Coca-Cola Company, Pepsi-Cola].

The rise of fast food was driven by 1950s car culture and suburban expansion [source: Smith]. What began as a convenient novelty—ordering burgers and fries at drive-thrus—quickly became a cornerstone of American life.

The latter half of the 20th century saw junk food and fast food explode in variety, affordability, and availability. Advances in production, packaging, distribution, and marketing—especially to kids—transformed occasional treats into daily staples for millions. Food scientists at major companies perfected formulas to keep consumers hooked.

The Science of Junk Food

The term 'Happy Meal' isn’t just a name—junk food is designed to be incredibly satisfying. This isn’t by chance. Food scientists and snack makers have meticulously crafted junk food to hit the perfect 'sweet spot,' ensuring we crave more and more (and more!).

It all begins in the mouth. A key feature of top-tier junk food is its mouthfeel. Cheetos, for instance, are renowned—or notorious—for delivering a burst of cheesy flavor without the heavy, greasy sensation of real cheese. Instead of feeling like salty fat bombs, Cheetos dissolve effortlessly in your mouth.

This phenomenon is known as vanishing caloric density [source: Moss]. Your brain uses mouthfeel to gauge calorie content. Since Cheetos melt away, they deceive your brain, making it easy to finish the entire bag.

Fast food leverages the science of mouthfeel to perfection. A hamburger and fries combo is undeniably rich in fat, and your mouth can sense it. However, food scientists have found that the greasy sensation of fries is perfectly offset by the sharpness of carbonated drinks [source: Cuda Kroen]. Plus, pairing salty with sweet adds an extra layer of satisfaction.

The food industry invests millions annually to perfect the ideal mix of mouthfeel and crunch that keeps consumers hooked. For instance, a $40,000 artificial chewing machine measures the precise pressure needed to bite into a chip—4 pounds per square inch is deemed the perfect crunch [source: Moss].

Junk food science is deeply rooted in evolutionary biology. Modern human brains developed during a time when survival depended on finding calorie-rich foods. As omnivores, we can process a variety of foods, but not all are equal in calories. Meat, for example, provides far more calories per bite than plant-based options.

To optimize calorie intake, our brains evolved to quickly identify the most energy-dense foods. Even in times of abundance, this instinct remains. When faced with a choice between an apple and a bag of chips, the ventromedial prefrontal cortex in our brain shouts, "Go for the chips! We might not survive tomorrow!" [source: Tedesco].

Health Effects of Junk Food

Excessive junk food consumption is directly linked to rising obesity rates and heightened risks of heart disease, Type 2 diabetes, and even depression.

A diet rich in sugar, simple carbs (like white flour, potatoes, and sugary drinks), and saturated fats is a leading factor in the obesity crisis. Over one-third of U.S. adults are obese, and children are mirroring this trend. Shockingly, 21% of teens aged 12 to 19 and 18% of kids aged 6 to 11 are obese—double the rates seen in the 1980s [sources: CDC, CDC].

How does junk food relate to Type 2 diabetes? Americans consume an average of 22 teaspoons of sugar daily, largely from high-fructose corn syrup in sodas and candy [source: Boseley]. Breaking down these simple carbs causes blood sugar spikes, prompting the pancreas to release insulin rapidly. Over time, these spikes exhaust insulin-producing cells, leading to Type 2 diabetes [source: Harvard School of Public Health].

Type 2 diabetes brings numerous health issues, including heart disease, nerve damage, kidney problems, a higher Alzheimer's risk, and severe foot infections that may necessitate amputation [source: Mayo Clinic].

Mental health also suffers from diets high in refined sugars, processed meats, and fatty dairy desserts. Studies show a strong link between junk food and increased depression rates [source: Zeratsky]. High fat and sugar levels can inflame and stress the brain, disrupting its chemical balance [source: BBC News].

What about the addictive nature of junk food? Research increasingly reveals that obese individuals, both adults and children, display classic addiction symptoms—uncontrollable overeating, heightened tolerance, and withdrawal signs—typically linked to substances like alcohol and drugs [source: Gray].

The U.S. government has attempted to impose stricter regulations on junk food, especially targeting its marketing and accessibility to kids. The FDA now mandates that restaurants and theaters display calorie counts on menus, and sugary sodas have been largely eliminated from school vending machines [source: Tavernise and Strom].

Despite this, fast-food giants continue to invest billions in advertising their calorie-dense, nutrient-poor products to children. In 2012, McDonald's spent 2.7 times more on ads than all producers of fruits, vegetables, bottled water, and milk combined [source: UCONN Rudd Center for Food Policy & Obesity].