How do ultra-processed foods hook our brain?

Scientists are uncovering parallels between junk food and addictive substances

For decades, scientists looked at addiction primarily through the lens of alcohol, cigarettes, and drugs like opioids. More recently, gambling behavior entered the view. Now, a new body of evidence is pushing researchers to ask: Can certain foods be addictive too?

A new review published in Pharmacological Researchopens in new tab/window examined over two decades of research to detail how ultra-processed foods — particularly those high in refined sugar and saturated fat — might trigger biological and behavioral changes that mirror addiction. The evidence repeatedly points to junk foods' ability to hijack the brain's reward system.

The first clues came from rats

In the early 2000s, obesity was largely viewed as a problem of metabolism and hormones. The possibility that some foods might be addictive was still outside the mainstream — until Avena and other researchers started feeding rats sugaropens in new tab/window.

Sugar repeatedly triggered the release of dopamine in reward-related regions in the brains of sugar-bingeing rats. Dopamine is a hormoneopens in new tab/window that helps motivate animals to seek out rewards.

"That's also the hallmark of drugs of abuse. Every time they're used, they release dopamine in these reward-related brain regions," Avena says. "So that kind of made sugar bingeing a little different than just eating regular food."

Whenever sugar was removed, the animals showed signs resembling withdrawal seen in drug and alcohol addiction. These studies don't mean a cookie and cocaine acts the same in the brain, but they prompted scientists to ask whether highly palatable foods do more than simply taste good.

Behavior telltales

Researchers at Yale approached the question from another angle — behavior.

They developed the Yale Food Addiction Scaleopens in new tab/window, which adapts criteria used to assess substance-use disorders to eating. For example, it evaluates whether people struggle to cut down or continue eating foods they know are not good for them. The current review highlights the scale as a tool for identifying food-addiction-like patterns in people.

Using this tool, a study of 120 adultsopens in new tab/window found that individuals who showed signs of food addiction were more likely to carry genetic traits linked to stronger dopamine activity and reward-driven eating. The study suggests that genetics might make some people more vulnerable to addiction-like eating.

"There really wasn't a singular study that put food addiction on the map," says Avena. Instead, researchers around the world collectively built momentum and moved the field.

What counts as food?

Avena is convinced that ultra-processed foods can be addictive and contribute to obesity and poor mental health. But critics still ask: How can food be addictive when humans need it to survive?

"We need food to survive, but we don't need ultra-processed food," Avena points out. Yet these foods account for more than half of the calories consumed in the average American household.

Defining what makes them so addicting is even harder. Unlike cigarettes or alcohol, there’s no single chemical compound that makes ultra-processed foods addictive, a challenge that has complicated their recognition as an addiction.

"My hope is that people just start to question what a food is," explains Avena. "What even is this stuff, and why are we eating it?"