Daniel Amen, M.D.

Clinical neuroscientist psychiatrist

By Daniel Amen, M.D.

Clinical neuroscientist psychiatrist

Daniel Amen, MD, is a clinical neuroscientist psychiatrist, physician, professor and 10-time New York Times bestselling author. He is a double board-certified child and adult psychiatrist and founder of Amen Clinics, Inc.

The Five Foods That Cause Brain Fog

Image by Tino Renato / Death to the Stock Photo

April 3, 2023

If you want to protect or improve your memory, you need to nourish your brain, and in particular your hippocampi.

This pair of thumb-sized structures located within the temporal lobes play a critical role in our ability to learn and remember. You may know them better as the hippocampus, the Greek word for “sea horse,” because they are shaped like the ocean creatures. Your daily habits are either fueling your hippocampi or shrinking them.


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Why are the hippocampi so important?

Think of the hippocampi as the gateway brain structures for memory formation. Long-term memories pass through these structures before being stored throughout the brain. For example, visual cues are routed to and stored in the occipital lobes, sensory cues go to the parietal lobes, sounds head to the temporal lobes, and so on.

When the hippocampi are healthy, they help with learning and memory. Shrinkage, or loss of volume, in these brain structures is associated with memory problems, cognitive decline, and in severe cases, Alzheimer’s disease and other dementias1.

Emerging brain-imaging research2 points to another reason the hippocampi are so important to us: They house stem cells that generate new neurons. This means the hippocampus is continually evolving throughout adulthood. One study3 suggests humans can produce as many as 700 new hippocampal cells a day, provided we put them in a nourishing environment.

That’s why it’s so important to know what nourishes your hippocampi—and what shrinks them.

3 ways to nourish your hippocampi:

Getting your heart pumping with aerobic exercise can increase hippocampal volume, according to a growing body of research, including findings in the British Journal of Sports Medicine4. And when it comes to memory and learning, more hippocampal cells are a good thing.

Research5 in Neuropsychology shows that exercising also protects the hippocampi from the detrimental effects of chronic stress (more on how stress shrinks the hippocampi below). Even better, you don’t need to run a marathon to get the benefits. A study6 in Hippocampus found that walking at a leisurely pace increased the volume of the hippocampus in older women.


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Engage in mental exercise.

The same way you work out your body, you also need to work out your brain to nourish your hippocampi. This may seem surprising, but a 2020 study7 found that playing 3D video games improves hippocampal memory in healthy young adults. Another bonus: The improvements lasted as long as four weeks after the trial ended. So go ahead and grab that joystick; just don’t overdo it as prolonged video gaming can have harmful effects8.

Other ways to give your hippocampus a mental workout include memorizing poetry or prose. For a study appearing in BMC Neuroscience, participants had to memorize 500 words per week for six weeks then took a series of memory tests and underwent a noninvasive imaging technique that provides information about cellular activity (proton magnetic resonance spectroscopy). The results? Improved memory and enhanced metabolic function in the hippocampi.

Put this into daily practice by memorizing things—say, your grocery list, song lyrics, or a poem—rather than constantly relying on your smartphone.

Learning new things is one of the best things you can do for your hippocampi. A study in Neuroimage9 found that intensive learning, such as going to law school or medical school, enlarged the hippocampi after just 14 weeks.

And going back to school isn’t the only way to enhance this brain structure. Simply learning to play a musical instrument can also help to increase the volume of the hippocampi, according to research10 in the Journal of Neuroscience. It also increases neuroplasticity—the brain’s ability to change in structure, function, and connections. Basically, this is what helps your brain adapt as you go through life.

So, sit down at the piano, grab a guitar, or pound the drums. Your hippocampi will thank you for it.


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3 things that shrink your hippocampi:

It’s common knowledge that stress can be harmful to physical health and emotional well-being. Unfortunately, it’s also damaging to your hippocampi. Animal studies11 show that chronic stress decreases the size of the hippocampi. In effect, extended exposure to stress hormones, such as cortisol, kills those new cells that are produced in your hippocampi. And having midlife stress11 has been associated with cognitive decline later in life.


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High blood sugar levels

Having high blood sugar levels, as seen in Type 1 diabetes12 and Type 2 diabetes13, is associated with smaller hippocampi. Even prediabetes and mildly elevated blood sugar levels have been linked to hippocampal shrinkage and memory problems.

In one study14, for example, in non-diabetics, dementia risk was 18% greater for people whose average blood glucose level was 115 milligrams per deciliter compared to individuals whose glucose levels averaged 100 mg/dl. As glucose levels rose incrementally, so did the risk for dementia. 


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Low omega-3 fatty acids

Did you know that most people are low in the omega-3 fatty acids EPA and DHA? At Amen Clinics, we took 50 consecutive patients and tested their omega-3 fatty acid levels. A shocking 49 out of 50 had suboptimal levels. In another in-house analysis, our research team looked at the brain SPECT scans of 130 patients and compared them with their EPA and DHA levels. The patients with the lowest levels of omega-3 fatty acids also had lower blood flow to the brain. This is concerning because low blood flow is the No. 1 brain-imaging predictor of future cognitive decline. The brain scans showed low blood flow in the right hippocampus, among other areas.

Increasing scientific evidence points to an association between omega-3 fatty acids, hippocampal size, and cognitive function. For example, a 2022 study in Neurology found that people with higher blood levels of omega-3 fatty acids had larger hippocampal volume and better abstract reasoning.

The takeaway

If you want to improve and protect your memory, stop shrinking your hippocampi and start nourishing them with these simple daily habits. You’re worth it.