Could an Unhealthy Diet Shrink Your Brain?
While eating an unhealthy Western diet may increase the size of your stomach, it could reduce the size of your brain, a new study suggests.
Researchers in Australia found that while consuming an unhealthy Western diet may reduce the volume of the left hippocampus, a healthy diet of fresh vegetables and fish may boost hippocampal volume.
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“We showed, for the first time in humans, that diet quality has a relatively strong relationship to hippocampal size,” says lead study author Felice N. Jacka, PhD, associate professor in the Division of Nutritional Psychiatry Research at Deakin University in Geelong, Australia.
“As the hippocampus is critical to learning and memory throughout life, as well as being a key part of the brain involved in mental health, this study underscores the importance of good nutrition for children, adolescents, and adults of all ages,” she says.
Jacka and her colleagues examined data from 255 individuals, ages 60 to 64 years at baseline, who had completed a questionnaire about their diets. They were classified as consuming either a “prudent/healthy diet” of fresh vegetables, salad, fruit, and grilled fish, or a “Western/unhealthy diet” of roasted meat, sausages, hamburgers, steak, French fries, potato chips, and soft drinks.
Participants underwent two T1-weighted 3-D structural MRI scans approximately 4 years apart to measure changes in left and right hippocampal volumes.
Compared to those with a healthy diet, those with an unhealthy diet showed a difference in left hippocampal volume of 203 mm3, which accounted for 62% of the average decline in left hippocampal volume during the 4-year study period.
Similar evidence linking diet and brain size in animals has been mounting for some time. Several studies have found that the animal equivalent of a “junk food” diet impairs hippocampal-dependent learning and memory.
Animal models have also demonstrated that a diet high in saturated fats and refined sugars has a very potent negative impact on neurotrophins, brain proteins that protect neurons from oxidative stress and promote new neuron growth in the hippocampus. On the other hand, studies have shown that food components high in antioxidants or protective lipids, such as omega-3 fatty acids, increase these protein levels.
“Recent research has established that diet and nutrition are related to the risk for depression, anxiety, and dementia; however, until now it was not clear how diet might exert an influence on mental health and cognition,” Jacka says. “This latest study sheds light on at least one of the pathways by which eating an unhealthy diet may influence the risk for dementia, cognitive decline, and mental disorders in older people. However, it also points to the importance of diet for brain health in other age groups.”
Jacka is president of the International Society for Nutritional Psychiatry Research, which was founded in early 2013 and now comprises more than 200 researchers and clinicians from across the globe, working to encourage collaboration, disseminate information, and influence policy and practice.
“This field has only been in existence for a few years, but is making an important impact in science and psychiatry,” Jacka says. “The critical new understanding that diet is of relevance to mental as well as physical health now gives us the opportunity to think about public health, prevention, and treatment strategies that focus on dietary improvement.”
She believes that interventions focused on improving diet and exercise to prevent physical illnesses such as heart disease, diabetes, and obesity, are also likely to help to prevent and treat depression and other mental disorders.
“Given that mental disorders account for the largest burden of disability across the globe, (this evidence) also throws into sharp relief the importance of addressing obesogenic environments to make healthy eating the easiest, cheapest and most socially acceptable option for people, no matter where they live,” she says.
—Colleen Mullarkey
Reference
Jacka FN, Cherbuin N, Anstey KJ, Sachdev P, Butterworth P. Western diet is associated with a smaller hippocampus: a longitudinal investigation. BMC Med. 2015 Sep 8;13(1):215.