Fellow junk food eaters can undoubtedly attest to the feeling of craving more, even when one thinks they have finished eating. Whether sweet, salty, or savory, junk food is a food of habit and repetition, compelling us to just have one more bite.
There are, of course, evolutionary reasons that we crave these kinds of simple flavors, embodied in sweets or fatty, salty foods. But there is also a more sinister element to our nation's junk food addiction: food manufacturers are manipulating our minds and bodies — spending millions of dollars over decades to engineer food that tastes good, but not good enough to make us stop eating. In addition, they play off of our own evolution as a species to help us develop dependencies on foods even when we know eating them is not in our best interest.
"The difference between a watermelon and something processed by a large company is that, for the latter, those foods are altered in ways to make them literally irresistible."
There are several ways that this happens. The first involves a quirk of human psychology known as sensory-specific satiety.
As the term hints at, sensory-specific satiety is what happens when you taste the same kind of food for so long that you grow bored with it. Even if your favorite food is ice cream or pizza, you would likely want something new if forced to eat nothing but ice cream or pizza for every meal.
Food manufacturers understand this, and as such when they design foods to hook in customers, they are clever about it. They keep in mind a factor known as "the bliss point," which refers to the exact combinations of saltiness, sweetness and other tastes that any given food item needs to be (a) delicious and (b) not quite delicious enough that you will feel satisfied after a small serving.
Quite to the contrary: Like many other businesses, food manufacturers want customers to buy as much of their product as possible. Customer satisfaction, though important, is not as much of a priority as customer demand — and getting your customer to crave a food item because they never quite feel satisfied after their last taste effectively establishes long-term and lucrative demand.
Take Prego spaghetti sauce, which was "optimized" by food industry scientist and mathematician Howard Moskowitz. Even though one may not think of spaghetti sauce as equivalent to candy, a single half-cup of Prego Traditional has more than two teaspoons of sugar — as much as at least two Oreo cookies. This is because industry research found that the sugar stimulated consumer tastebuds enough to make them crave more and more of the spaghetti sauce, even though this sauce does not taste much like counterparts that were primarily tomato-based.
In addition to leaning into the distinct psychology behind how humans respond to tastes, food industry experts also look into how our bodies evolved to process different types of nutrients. Evolutionary psychologists argue that the body craves things like fats, sugars and even salt in order to shore up its stores of energy so that it will suffer less during periods of famine. This is why — when a junk food fan eats something like a greasy fried chicken leg or a bag of sugar-coated candy — their brain releases chemicals which tell them to enjoy themselves and indulge. Your body does not understand that there are "good foods" and "bad foods"; it simply processes this food as being something it likes, and therefore encourages you to chow down on it again and again.
"When we taste something and when those nutrients hit our gut, there are signals in the brain — pleasurable signals — that make us think, 'This is really delicious! I like this a lot!'" explains Dr. Alexandra DiFeliceantonio from Fralin Biomedical Research Institute at Virginia Tech Carillon. "That's probably due to a class of chemicals called opioids."
Yes, those are the same opioids that refer to the addictive pharmacological drug of the same name. Opioid peptides in your brain are very similar neurochemically from the ones that you can put in your body with pills.
In addition to these opioids, the body also releases a neurochemical called dopamine, which DiFeliceantonio compared to a "tag," figuratively poking your body and saying, "'Oh, go do that again! That's something that you should eat again. That's something that you should go do.' It has to do with motivation and with learning, and both these signals are really important for our behavior."
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In and of itself, there is nothing inherently sinister about this aspect of human neurochemistry. Indeed, the same signals that make a person crave cotton candy or a Big Mac could in theory also draw them toward a crunch carrot, juicy orange or tender strip of lean turkey. Yet according to Dr. Nicole Avena, an assistant professor of neuroscience at Mount Sinai Medical School and a visiting professor of health psychology at Princeton University, there are important differences in how the brain responds to highly-processed junk foods versus how it processes something like a banana or grilled flounder.
"It seems that foods with added sugars are 'enjoyed' differently, as our brain seems to be more sensitive to higher amounts of sugar than we would typically see in nature (like, for example, in an apple)," Avena wrote to Salon. This is evidenced, among other things, by the contrasting ways in which humans eat the highly-processed, chemical-laden foods and the ways in which they eat those that appear in nature.
"People are not experiencing this with things like beans, baked chicken breasts and fruit, even if they really like them," Dr. Ashley Gearhardt, an associate professor at the Department of Psychology at the University of Michigan, told Salon. To illustrate her point, Gearhardt turned to one of her own favorite foods: Watermelon.
Neuroscientist Dana Small suggests that junk foods which combine sweet flavors with fat form a combination not found in nature except in breast milk — and which therefore perhaps stimulate a primal memory.
"I love watermelon, it's delicious, but nobody sits down and eats the whole watermelon," Gearhardt observed. The difference between a watermelon and something processed by a large company is that, for the latter, those foods are altered in ways to make them literally irresistible. This happens when companies use a combination of salt, sugar and fat to create foods that overstimulate the taste buds — and yet are designed to never quite leave you feeling satisfied. Even though saturating foods in salt, sugar and fat fuels the obesity epidemic — and does not necessarily provide consumers with the best culinary experience — it guarantees that customers will keep coming back for more by overstimulating one's feeling of taste pleasure in exactly the right ways. Since the companies' view their foremost responsibility as being to their shareholders, that is in itself a good enough reason to continue preparing foods with excessive salt, sugar and fat.
"Salt, sugar, and fat are big players in junk food because the body is wired to detect them and signal the reward centers via the taste buds for sugar and salt, and the trigeminal nerve for fats, with more signalling in the gut," explained Pulitzer Prize-winning journalist Michael Moss, author of "Salt Sugar Fat," in an email to Salon. He also pointed out that companies are clever in appealing to senses other than taste. They will intentionally make their junk foods colorful and vibrant to look at, and have textures that are pleasing to the touch. Sound can also play a role, with Moss noting that one experiment found customers are more apt to buy potato chips that crunch loudly. Even memory is important, with Moss referring to the research by Yale University psychologist and neuroscientist Dana Small which suggested that junk foods which combine sweet flavors with fat form a combination not found in nature except in breast milk — and which therefore perhaps stimulate a primal memory through a part of the brain known as the striatum.
The underlying problem is that the human body is like a machine that needs fuel to survive, but has programming which has not been updated to figure out how to make sure that it craves the healthiest nutrients. We are instead programmed to simply gravitate toward as many calories as possible.
"We detect the calories in what we eat, through sensors on the tongue and possibly in the gut, and we're drawn to foods that have more calories because for most of our existence getting enough calories was life and death," Moss wrote to Salon. "But we can't distinguish between nutritious calories and the empty ones in junk food, and so we get just as excited about 300 calories in a candy bar as we do over those in more wholesome food."
Does all of this science mean that one can consider junk food to be "addictive"? It depends on who you ask and how you define the term.
For his part, Moss resists the word "addiction" on the grounds that it is "a lay term and generally spurned by the medical community because it's vague and unscientific." As far as lay definitions go, however, Moss certainly acknowledged that it applies to junk food insofar as it conventionally refers to "a repetitive behavior that some people find difficult to quit," analogous to how consumers interact with alcohol, cigarettes and other drugs. He also pointed out that when manufacturers boost sales with "words like crave-ability, snack-ability and more-ishness" it becomes "difficult for them to draw a line between that and compulsiveness on our part."
Avena, by contrast, is quite unambiguous about using the word "addiction."
"We have done a lot of work to characterize food addiction," Avena told Salon. Her research has found that junk foods trigger all of the same symptoms associated with other kinds of addiction including withdrawal, cravings and bingeing behavior.
"When you look at the criteria for addiction that are in the DSM (Diagnostic and Statistical Manual for Mental Disorders--the book that the American Psychiatric Association uses to describe the criteria that need to be met in order to be diagnosed with mental health conditions), junk foods meet all of the criteria," Avena pointed out.