Junk food could damage your memory in just 4 days, a study reveals

We all know that ultra-processed food, high in saturated fats, isn’t good. But if you thought you had to eat a lot of hamburgers, pizzas, and fries for a long time to suffer the consequences, you’re wrong.

Researchers at the University of North Carolina School of Medicine discovered that these foods can affect our memory in as little as four days. In simpler terms: junk food can make you forget where you put your keys or what you were going to buy at the supermarket… all in less than a week.

Diet influences the brain much more than we think

We’ve known for years that junk food affects our mood. Researchers from the University of Las Palmas de Gran Canaria and the University of Granada had discovered that processed pastries and fast food increase the risk of depression.

On the other hand, researchers at the University of California observed that consuming foods high in trans fats increased irritability and aggression. However, in this instance, the effects of junk food have been observed in cognitive functions.

The study, published in the journal Neuron, offers a unique perspective on how junk food alters the brain’s memory center, increasing the risk of cognitive dysfunction. In the experiment, researchers fed mice a high-fat diet similar to that of junk food. After four days, CCK interneurons in the brain’s memory center were abnormally activated.

The neurological mechanism by which fats block memory

A high-fat diet impairs memory capacity within days because it overstimulates key neurons in the brain’s memory center. A specific group of cells in the hippocampus, called CCK interneurons, become hyperactive after consuming a high-fat diet, because the brain loses its ability to process glucose.

CCK interneurons regulate the activity of excitatory neurons, which are involved in the storage and retrieval of memories. They ensure the necessary balance between excitation and inhibition for memory to function correctly. When these interneurons become hyperactive, they inhibit the neurons that should be encoding new memories, thus acting as a “brake” within the memory circuit.

Everything seems to indicate that high-fat foods affect glucose availability in the brain, making it less efficient at “taking it up.” In response to this metabolic stress, a protein called PKM2 is activated, acting as a switch in some neurons. The extremely simplified process would be:

1. A diet high in saturated fats decreases metabolic efficiency, preventing the brain from making good use of glucose, particularly affecting the area linked to memory.
2. Decreased glucose puts the brain into “alert mode,” generating the PKM2 protein, which in turn triggers the activity of CCK interneurons.
3. The overactivation of CCK interneurons ends up slowing down the functioning of excitatory neurons that encode memories.

Therefore, even though excitatory neurons want to store new information, they remain blocked.

Why is it so important to us?

Although the study refers to animal models, the underlying mechanisms are plausible for humans because our hippocampus also depends on glucose availability, inhibitory interneurons have similar functions, and the high-fat Western diet has already been linked to cognitive decline.

Furthermore, the fact that the changes occur rapidly (within days) underscores that not only does cumulative damage matter, but the brain may be particularly vulnerable to metabolic imbalances.

In this regard, neuroscientists stated that they were aware that diet and metabolism could affect brain health, but they did not expect to find such a specific and vulnerable group of brain cells, nor that they would be affected so soon.

“What surprised us most was how quickly these cells changed their activity in response to the lower availability of glucose, and how this change alone was enough to impair memory,” they noted.

So now you know that what you eat isn’t just reflected in your waistline or your heart; it also affects your neurons. So if you’ve been feeling a bit forgetful lately, it might be a good idea to start by reviewing your diet.

Source:

Landry, t. et. Al. (2025) Targeting glucose-inhibited hippocampal CCK interneurons prevents cognitive impairment in diet-induced obesity. Neuron; S0896-6273(25)00622-1.