Over and over studies find that a person's diet is linked to health and diseases, and now a study finds that an unhealthy diet is linked to shrinkage of the brain, specifically the volume of the left hippocampus. The biggest effects on the hippocampus are found with both greater consumption of an unhealthy diet and lower consumption of a healthy diet. The hippocampus is a brain structure associated with both learning and memory, as well as mood regulation, and is specifically implicated in depression. In dementia and Alzheimer's disease, the hippocampus is one of the first regions of the brain to suffer damage.
So....you want to protect your hippocampus from shrinkage. The researchers themselves suggest that the effects may be reversible, and suggest "dietary interventions to promote hippocampal health". Once again, a healthy diet means lots of plant-based foods (for example, a Mediterranean based diet with lots of fruits, vegetables, legumes, nuts, berries, seeds), and decreasing a Western-style diet with highly processed foods, low fiber, lots of meat, fat, and refined sugars. From Medscape:
Consumption of an unhealthy Western diet characterized by meat, hamburgers, chips, and soft drinks, may reduce the volume of the left hippocampus, whereas a healthy diet of fresh vegetables and fish may increase hippocampal volume. In a study of more than 250 individuals, investigators found that during a period of 4 years, there was a difference of more than 200 cubic millimeters in hippocampal volume between individuals who ate a healthy diet and those who consumed an unhealthy diet.
"These findings suggest the potential for dietary interventions to promote hippocampal health, decrease age-related atrophy, and prevent negative health outcomes associated with hippocampal atrophy," they add. Previous studies have shown that quality of diet is associated with depression and cognitive health. Animal research indicates that this may be mediated by changes in the hippocampus. Specifically, a high-fat diet reduces brain-derived neurotrophic factor levels, which impairs neuronal plasticity, learning, and behavior.
For the current study, the researchers examined data from the Personality and Total Health Through Life Study on 255 individuals aged 60 to 64 years at baseline....Participants were classified as consuming either a "prudent/healthy diet," consisting of fresh vegetables, salad, fruit, and grilled fish, or a "Western/unhealthy diet," consisting of roast meat, sausages, hamburgers, steak, chips, crisps, and soft drinks. A 1-point difference on an 11-point scale of consumption of each type of diet corresponded to 1 standard deviation difference....
The investigators found that for each standard deviation increase in consumption of the "prudent diet," there was a 45.7 cubic millimeter increase in left hippocampal volume. In contrast, each standard deviation increase in consumption of the Western diet was independently associated with a 52.6 cubic millimeter decrease in the volume of the left hippocampus. The impact of diet on hippocampal volume was independent of age, sex, education, labor-force status, depressive symptoms, use of medication, physical activity, smoking, hypertension, and diabetes.
The difference in left hippocampal volume between those with a healthy diet and those with an unhealthy diet was 203 cubic millimeters, which accounted for 62% of the average decline in left hippocampal volume during the 4-year study period. Interestingly, there were no significant associations between right hippocampal volume and dietary patterns, although there was a nonsignificant relationship.
In an interview with Medscape Medical News, Dr Jacka pointed out the the research was observational in nature, and therefore it cannot be stated for certain that the Western diet is causing the hippocampus to shrink. "However, there have been many studies in animals that show that a diet high in saturated fats and refined sugars has a very potent negative impact on the brain proteins (neurotrophins) that both protect neurons from oxidative stress and promote the growth of new neurons in the hippocampus," she said.
"Similarly, there are many studies that show that food components high in antioxidants or protective lipids, such as omega-3 fatty acids, increase levels of these proteins. There are also many studies showing that the animal equivalent of 'junk food' diets impair hippocampal-dependent learning and memory." Crucially, Dr Jacka believes that switching from a Western to a "prudent" diet would lead to increases in hippocampal volume."From what we know so far, it seems that neurotrophin levels and hippocampal volume and function are relatively labile and readily influenced by environmental exposures, including both diet and physical activity," she said. "So there is every reason to believe that the noxious impact of unhealthy diets can be reversed by dietary improvement and vice versa."
This is of particular importance given that the latest Global Burden of Diseases data from The Lancet indicate that unhealthy diets are the leading cause of early mortality worldwide and that mental disorders are the leading cause of global disability. With a growing body of evidence showing that unhealthy diets are linked to mental, neurodegenerative, and neurodevelopmental disorders, Dr Jacka said the findings have "enormous implications for public health."
"It's the first time that a dietary pattern has been linked to specific changes in the brain. We've known for a long time that there's a correlation between dietary pattern and the risk of a number of brain illnesses, like depression and dementia, and the mechanism behind this, we believe, involves neuroplastic processes of how food affects brain growth. This is the first study that's really shown that quite conclusively," he said. BMC Med. Published online September 8, 2015. Full text
The blue structure in the brain is the hippocampus. Credit: BrainHQ