How Junk Food Tricks Your Brain and Changes What You Crave

All living organisms need energy (calories) to survive. Over millions of years, our brains have evolved powerful systems to help us detect, seek out, and store energy, primarily through food⁽¹⁾.

Today, those systems are running into a modern problem: highly processed food-like products that deliver more energy than our bodies need in ways our brains find unusually rewarding.

Why the Brain Cares So Much About Food Cues

The human brain is a fast learner. Over time, it links sights, smells, and sounds in the environment with past experiences of eating. That’s why the smell of fries or the sight of a familiar fast-food logo can make you crave food, even when you’re not hungry⁽²⁾.

This kind of learning is called cue association, and it evolved to help us survive in environments where food was scarce. But in today’s world, where high-calorie, low-nutrient foods are everywhere, the same system can be hijacked to work against us⁽³⁾.

How Food “Talks” to the Brain Without You Noticing

When we eat, our bodies send silent messages to the brain. These signals help the brain learn how much energy a food contains and how it makes us feel.

• Fat. Fat sends signals through a key nerve pathway (the vagus nerve) to the brain, saying, in effect, “This is rich, long-lasting energy.”
• Sugar. Once burned by cells triggers dopamine (the brain's “feel-good” chemical) which makes us more likely to remember and seek out that food again.

The more energy a food delivers, the stronger the brain’s response becomes. It’s a feedback loop, and junk food supercharges it.

Junk Food Doesn't Just Taste Good, It Changes the Brain

Modern processed snacks loaded with sugar and fat deliver a reward so powerful that it can alter how the brain works. This isn't theory either. Studies show that high-fat, high-sugar diets can cause the brain to rewire itself in ways that look remarkably similar to what happens with addictive drugs like cocaine⁽⁴⁾.

What changes?

• The brain starts craving these foods more often, even when you're full.
• Healthier foods, like fruits or vegetables, seem less appealing.
• Environmental cues (such as ads, smells, and packaging) become harder to ignore.

This is more than craving a cookie. It’s a brain that’s been reprogrammed to need it.

This Happens in Humans, Not Just Lab Animals

Researchers recently tested this idea in a group of healthy-weight adults. For 8 weeks, participants were asked to eat two snacks a day. One group received high-fat, high-sugar snacks such as milkshakes. The other group ate snacks with similar calories but lower fat and sugar, and higher protein⁽⁵⁾. 

Despite no significant weight gain in either group, the results were striking:

• The high-fat, high-sugar group began to enjoy low-fat snacks less.
• Their brains showed stronger responses to food-related cues and during actual food consumption.
• Even their learning circuits changed and adapted in ways that made them more responsive to non-food patterns and associations.

In other words, the brain wasn’t just learning to prefer junk food. It was becoming better at learning patterns, just not always in helpful ways.

Figure: High-fat/high-sugar dietary intervention enhanced brain activation related to associative learning (adapted from Edwin et al 2023⁽⁵⁾) 

Why This Matters, Even for Healthy People

For a long time, scientists believed that weight gain and obesity stemmed mostly from genetics or poor self-control⁽⁶⁾. 

But these new findings suggest another possibility:

Simply being exposed to a high-fat, high-sugar diet, even without gaining weight can alter how your brain values food, how it learns, and what it craves⁽⁷⁾.

That has major implications for people living in environments where processed food is cheap and widely available. It's not just a matter of willpower, it’s biology. A brain repeatedly exposed to junk food becomes more likely to seek it out, even when it “knows better.”

What’s Going on in the Brain?

These changes show up in several key brain areas⁽⁸⁾:

• Midbrain and prefrontal cortex: Regions involved in decision making and reward-seeking become more sensitive to food cues.
• Insular cortex: This area helps process the body’s internal states, like fullness or satiety. With high-fat, high-sugar exposure, it becomes more reactive to food even if you’re not actually hungry. 
• Dopamine system: Junk food increases short-term dopamine spikes while possibly lowering baseline levels, reducing your brain's ability to feel satisfied over time.

These aren’t minor tweaks, they’re fundamental shifts in how the brain processes reward and makes choices.

From Adaptation to Addiction?

From an evolutionary perspective, these brain changes may have once been helpful. In environments where food was scarce, learning quickly about high-energy foods gave our ancestors an edge.

But in modern settings that offer easy access to calorie-dense snacks, these same adaptations can become maladaptive. Over time, the brain’s reward system becomes tuned to seek more and more, even when the body doesn’t need it⁽⁹⁾.

Some animal studies even show that these changes can persist after the junk food is taken away, and may pass on to offspring.

What the Evidence Tells Us So Far

The current study and others like it suggest a few important takeaways:

• Repeated exposure to junk food rewires brain circuits related to learning, reward, and food preference.
• These changes occur even without weight gain or obvious metabolic problems.
  They may help explain why some people struggle to resist certain foods, especially in environments where healthier options are limited.
• Importantly, this research challenges the idea that people must first become overweight before brain changes happen. It may be the other way around: diet-induced brain changes could come first, nudging people toward future weight gain.

What Can Be Done?

This isn’t just a personal health issue, it’s a widespread public health challenge. If junk food can quietly reprogram the brain in healthy people, then the focus needs to shift from blaming individuals to changing their environment.

Some helpful steps:

• Make healthier snacks (real food) more available and appealing, especially in schools and communities. Unfortunately, leaving this up to companies who profit off these addictive properties is not going to happen, so it's up to you to be aware of the choices you make and where you are shopping for food.
• Reduce exposure to ultra-processed food-like products high in sugar and fat.
  Educate people (especially young people) on how food affects not just their bodies, but their brains⁽⁵⁾.

The Bottom Line

Highly processed food-like products don’t just tempt your taste buds, they reshape your brain’s wiring, and it's not an accident. They are designed that way. Over time, they can change how you learn, what you crave, and how you make decisions about food.

That’s why the occasional indulgence isn’t the real issue. It’s repeated exposure that matters. When your brain starts learning from every bite, the lessons it takes in can shape future behavior in powerful ways.

So the next time you reach for that glazed donut, ask yourself: Is this the habit I want my brain to keep learning?

The good news is this simple question can also be applied to other areas like drinking alcohol, for example.  The occasional indulgence isn’t an issue, but repeated exposure that I believe rewires the brain.  This can be said for any other addiction/habit, whether it is good or bad. 

I believe the repeated exposure to something forms neural circuits/pathways and ingrains habits that our brain seeks out.  The key is to ensure these habits are healthy, positive, and productive. 

If you have cravings for junk food during the day, a protein shake is good replacement.

STEEL has an entire line of delicious whey and dairy-free proteins in a variety of flavors that can satisfy that craving and actually contribute to your daily nutritional goals!

References: 
    1.    Betley JN, Xu S, Cao ZFH, et al: Neurons for hunger and thirst transmit a negative-valence teaching signal. Nature 521:180-185, 2015
    2.    de Araujo IE, Schatzker M, Small DM: Rethinking Food Reward. Annu Rev Psychol 71:139-164, 2020
    3.    Jansen A, Theunissen N, Slechten K, et al: Overweight children overeat after exposure to food cues. Eat Behav 4:197-209, 2003
    4.    Adams WK, Sussman JL, Kaur S, et al: Long-term, calorie-restricted intake of a high-fat diet in rats reduces impulse control and ventral striatal D2 receptor signalling - two markers of addiction vulnerability. Eur J Neurosci 42:3095-104, 2015
    5.    Edwin Thanarajah S, DiFeliceantonio AG, Albus K, et al: Habitual daily intake of a sweet and fatty snack modulates reward processing in humans. Cell Metabolism 35:571-584.e6, 2023
    6.    Loos RJF, Yeo GSH: The genetics of obesity: from discovery to biology. Nat Rev Genet 23:120-133, 2022
    7.    Tellez LA, Medina S, Han W, et al: A gut lipid messenger links excess dietary fat to dopamine deficiency. Science 341:800-2, 2013
    8.    de Araujo IE, Geha P, Small DM: Orosensory and Homeostatic Functions of the Insular Taste Cortex. Chemosens Percept 5:64-79, 2012
    9.    O'Connor RM, Kenny PJ: Utility of 'substance use disorder' as a heuristic for understanding overeating and obesity. Prog Neuropsychopharmacol Biol Psychiatry 118:110580, 2022