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Source: wikimedia commons

You are what you eat. This simple adage serves us well when we think about a healthy diet full of a variety of whole foods brimming with protein, natural fats, and carbohydrates packed with all the necessary micronutrients that come along for the ride. In contrast, a poor diet is one filled with convenience “fast food” loaded with industrial fats, refined grains, and sugar-sweetened treats. There is plenty of evidence showing us that a good diet is associated with all sorts of physical health benefits…greater longevity, less obesity, diabetes, heart disease, and even cancer. For a long time, however, it was felt that diet didn’t have much influence on mental health. After all, mental health problems were considered to be due to stress in the environment, such as the loss of a loved one, or another traumatic experience, along with genetic influences.

More and more in recent years we’ve collected the data to show that a poor diet counts as one more environmental stress, leaving the brain less resilient and less able to cope. There are all sorts of theories as to why a healthy diet makes for a healthy brain…from the obvious finding that all sorts of nutrients like omega 3 fatty acids, minerals, and b vitamins that might be lacking in a poor diet to more oblique theories such as how a whole foods diet will impact the body’s microbiome and its effects on the brain. Some folks may be especially sensitive to certain components of a Western diet (such as the refined sugars, gluten, or trans fats), leading to psychological symptoms when one consumes those particular foods.

It’s one thing to have a theory, it’s quite another to get data that shows the Western diet might be causing actual brain damage over time. We already knew from animal studies that highly refined diets led to shrinkage of a particular area of the brain associated with depression and dementia, the hippocampus. When parts of the brain shrink, we know that cells are dying off. In human beings, could those lunches of chips and soda lead to the death of neurons in the hippocampus?

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Source: wikimedia commons

Observational studies have shown that a healthy diet pattern is associated with lower risk of depression and dementia. In the recent PATH study in Australia, seniors were followed for several years using dietary pattern questionnaires and serial MRIs. For the first time, researchers now have data in humans that a healthy diet pattern is also associated with a bigger hippocampus! The inverse is also true…the more junk food a person reports eating, the smaller his or her hippocampus tends to be. These associations hold when other confounding variables, such as age, gender, wealth, smoking, education, and activity level are factored in.

How could a poor diet actually shrink the brain over time? Well, the mechanisms are complicated, but it seems to boil down to a process of inflammation. Elements of a healthy diet, such as omega 3s and antioxidants and an appropriate mix of natural vitamins and minerals allows the brain to be efficient in producing energy and helps all the neurons stay healthy and fix any problems. The hippocampus is a place in the adult brain where you can make new nerve cells, and a healthy diet allows for neurogenesis and repair. A poor diet, on the other hand, leads to messy, inefficient energy production with lots of by-products that can lead to nerve damage and bring the brain’s immune system to high alert. The immune system in this case causes more problems than it solves, inflammation gets out of control, and damaged nerves can’t repair themselves, so eventually the cells die off. In the hippocampus, this process could lead to a greater vulnerability to depression and dementia. Scary stuff. 

The same study cohort also shows that smaller hippocampal volumes are associated with a higher fasting glucose level, another marker of whole body inflammation and a more “Western-style” diet.

Don’t be afraid of a bag of potato chips every now and again, but if the majority of the calories you consume comes in colorful packages designed by expensive graphics design firms with ingredients lists a mile long, you would be better off, both physically and mentally, getting whole foods from the store or farmer’s market and doing some home cooking. We know that just talking to seniors about a healthier diet can reduce depression scores by nearly half. For mental health, working more whole foods into the diet is a no-brainer.

Copyright Emily Deans MD

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