How junk food outsmarts our brains—by hiding in our memories

National Geographic

17-04-2025

New research reveals that memories of fatty and sugary foods are encoded in the hippocampus, helping explain why some cravings feel impossible to resist. Cravings may feel impulsive, but new research suggests they're often rooted in memory. Scientists have found that the brain encodes high-calorie foods in a way that can quietly influence what we eat—even when we're not hungry. Photograph by Heather Willensky, The New York Times/Redux
The next time you remember a chocolate bar in a desk drawer, your brain might not just be recalling it—it could be actively pushing you to seek it out.
A recent study published in Nature Metabolism suggests that specific neurons in the hippocampus log the sensory and emotional details of calorie-rich food. In mice, these neurons triggered cravings, leading to overeating—even when the animals weren't hungry. When researchers silenced these neurons, the rodents reduced their sugar intake and avoided diet-induced obesity.
'Every animal needs to eat, so we get hunger drives to help with our survival,' says Guillaume de Lartigue, an associate member of the Monell Chemical Senses Center and co-author of the new study. Traditionally, scientists have distinguished between metabolic hunger—the body's need for energy—and hedonic hunger, which arises when food looks or smells tempting. But this study adds a third layer: memory-driven hunger.
(Here's how ultra-processed food harms the body and brain.)
Though the research was conducted in animals, it supports a growing body of evidence that memories of fat and sugar can quietly shape our eating behavior—often without our awareness. And in a world where high-calorie foods are everywhere, those neural patterns may help explain why some cravings feel impossible to resist. Why our brains are no match for junk food
The job of any organism is to understand how to navigate and make the best choices to obtain food in their environment, says Dana Small, a psychologist, neuroscientist, and the Canada Excellence Research Chair in Metabolism and Brain.
In early human history, when calories were scarce, we learned to use sensory cues—smell, sight, and location—to identify energy-rich foods, says Small. After eating, the brain stores that information along with how the food made us feel, creating a mental 'database' of flavors and their effects. Essentially, when we eat, we're subliminally 'integrating the external and internal worlds, which is what memory is,' says Small.
These signals influence dopamine release in the brain's reward pathways. The brain then updates the value of a food based on this information and uses that data when you reencounter the flavor. So the next time you pass a bakery, for example, that internal record, or memory, activates, sparking a craving.
(Here's what dopamine, the 'happy hormone,' actually does.)
The Monell study also found that memories of fat and sugar are stored via separate pathways, both leading to dopamine. While most foods contain either fat or carbohydrates, ultra-processed foods contain both. Foods that combine these macronutrients can activate both paths simultaneously, as seen in the mice from the study, potentially triggering an amplified reward response, which may help explain why such foods are tough to resist.
In today's world, these high-calorie foods that contain this powerful combination are everywhere and easily accessible, overwhelming our brain's natural decision-making systems and making it harder to choose healthier options. Can therapy or medication help you stop craving junk food?
The good news is that the brain is adaptable. Just as it learns to crave certain foods, it can also learn new responses, says Amy Egbert, an assistant professor of psychological sciences at the University of Connecticut. The first step is to identify the cause of the craving. Is it based on hunger, emotion, or something else?
Once you understand the trigger, you can begin to unlearn the craving loop. That's where therapeutic approaches can come in. 'Exposure-based therapies and cognitive techniques are some of the most effective tools we have,' Egbert says. These methods can help individuals unpack how they developed certain food relationships and retrain their responses over time.
(Are ultra-processed foods as addictive as cigarettes?)
Small agrees that exposure therapy can help but says it doesn't generalize across flavors. Each one must be addressed individually, making the process labor-intensive. She adds that medications like GLP-1 agonists—including Ozempic—show promise in dampening the brain's reward signals after eating 'It can reduce the conditioning, reduce the dopamine release, and help reduce cravings in the brain,' Small says.
However, it's worth noting that while these medications may be able to manage appetite in the short term, they don't address the root cause of overeating. 'Having a drug that dampens that is great because it helps us to manage our food intake. But, once you come off of it, the underlying problem is still there,' says de Lartigue.
While researchers are still exploring exactly how these medications affect the brain's reward and memory systems, the best bet is to focus on how and why we eat what we do and address that alongside any pharmaceutical interventions. How to train your brain to resist junk food
Modern life makes resisting cravings especially difficult. Our daily lives work against us as well–in many cases, we don't have the resources, such as time or money, to make healthier foods that are just as delicious to our systems. And complicating matters further is that the brain can form a food memory after just one exposure, making cravings nearly impossible to resist.
(Can't stop thinking about your next meal? That's 'food noise'—here's how to stop it.)
Still, de Lartigue argues that simply knowing that memory can drive our food intake is powerful. 'The knowledge that memory itself is a trigger for overeating can help you change your behavior. A lot of these things are subconscious, so if you bring awareness to them, you can interrupt the cycle of memory and craving,' he says.
Cravings may feel impulsive or indulgent, but they're often built on deeply ingrained neural blueprints. The more we understand those patterns, the better chance we have to reshape them—and take back control over what we eat.