Some studies claim to find that junk food is as addictive as drugs, but experts say that what actually determines how addictive something is, and whether an individual becomes addicted, is complex.
In the most recent headline-grabbing research, a study in rats found that a brain region important for pleasure was activated more strongly when the animals were exposed to Oreos compared to cocaine. A 2011 study found that the brains of people with "food addiction" reacted to junk food the same way that the brains of people with drug addictions react to drugs.
But just because junk foods and drugs may activate the same area of the brain does not mean they are addicting, experts say.
Here's what we know about the development of addiction.
What is addiction?
Addiction has both a biological and behavioral component.
Our brains are hard-wired to find certain things pleasurable, such as eating and having sex. This brain "reward circuitry" makes sure we carry out behaviors we need to survive, said Brad Lander, a psychologist at Ohio State University Wexner Medical Center. [10 Easy Paths to Self Destruction]
"Anything that stimulates the reward pathway is going to be interpreted as something that’s necessary for life and needs to be repeated," Lander said.
But many things that are not, in fact, necessary for life can stimulate this reward circuitry, including drugs, sugar, fatty foods, and even behaviors such as gambling and exercise, said Dr. Joseph Frascella, director of the division of clinical neuroscience and behavioral research at the National Institute on Drug Abuse. The pleasure we get from these substances comes from the release of dopamine in the brain, which reinforces the behavior.
However, stimulating this circuitry does not guarantee addiction, it only means that substances that act this way have the potential to be addictive, Frascella said.
Edythe London, a neuropharmacologist and director of the University of California Los Angeles Center for Addictive Behaviors, agreed.
"Just because there's a commonality in the brain circuitry involved in the response to engaging in these activities, it doesn't mean that they're all addictive," London said.
A major hallmark of addiction is a loss of control regarding use of a substance — such as taking more than you should, or escalating your use despite knowing the substance is harmful — as well as cravings for it, Frascella said.
Addicted people may obsessively think about getting the substance, so much so that it dominates their life, and they experience withdrawal symptoms when they quit, Lander said.
Ultimately, for an addicted individual, use of a particular substance has a negative impact on the person's life, London said.
It's hard to determine whether one substance is more, less or equally addictive compared to another, at least for people.
That's because so many factors influence the propensity to addiction, including availability of the substance, and a person's genetics as well as previous experience with drugs, Frascella said.
That said, the intensity of the drug — such as the rush or hit a person feels when they take it, as well as the speed with which this happens, can factor into a drug's addiction potential. Drugs that provide a powerful "hit" rather quickly may lead to addictions that are more difficult to treat, Lander said.
The best way to measure the addictiveness of a substance is how hard an animal will work for it, London said.
"Animals will work very, very hard for cocaine. They will starve themselves if they're allowed to," London said. However, studies in animals do not always translate to people.
Can you be addicted to sugar?
Although many people like sweets, and would likely choose chocolate cake over fruit for dessert, this does not mean they're addicted to sugar, Frascella said.
But a small percentage of people may truly become addicted, experiencing the type of loss of control around food that is characteristic of addiction, Frascella said.
London said she would not call this a sugar addiction, but rather, "pathological obesity."
"There are clear similarities between pathological obesity that involves uncontrolled eating, and addictions," London said.
People who are obese have fewer dopamine receptors in a brain region called the striatum, which is also a characteristic of people who are addicted to drugs, London said.
"With the explosion of obesity in the United States, it's clear that [some] people have uncontrolled caloric intake," London said.