By Joseph E. Scherger, MD, MPH
Vice President, Primary Care, Eisenhower Medical Center; Clinical Professor, Keek School of Medicine, University of Southern California
Dr. Scherger reports no financial relationships relevant to this field of study.
SYNOPSIS: Greater intake of unhealthy food and lower intake of nutrient-dense food is associated with a smaller hippocampus over 4 years in adults 60-64 years of age.
SOURCE: Jacka FN, et al. Western diet is associated with a smaller hippocampus: A longitudinal investigation. BMC Medicine 2015;13:215-222.
A team of investigators from Australia used a database of 2551 adults living in and around Canberra who participated in the Personality and Total Health (PATH) Through Life project starting in 2001. A subgroup of 255 patients were in the age 60-64 cohort and had both a diet survey and an MRI initially, then four years later. Diets were self-reported and put on a scale from “prudent” (healthy) emphasizing fresh vegetables, salad, fruit, and grilled fish to “Western” (unhealthy) emphasizing roast meat, sausages, hamburgers, steak, chips, and soft drinks.
Significant differences were found with diet and change in the size of the hippocampus on MRI. Every 1 standard deviation increase in the healthy dietary pattern was associated with a 45.7 mm larger left hippocampal volume, while a higher consumption of the unhealthy foods was independently associated with a 52.6 mm smaller left hippocampal volume. These relationships were independent of variables such as age, gender, education, work status, depressive symptoms, medication, physical activity, smoking, hypertension, and diabetes.
This is the first study that demonstrated a relationship between diet and the size of the hippocampus in humans. Such an association has been shown in animals.1,2 The authors proposed a variety of mechanisms for this change, such as inflammation, oxidative stress, and the gut microbiome.
The hippocampus is a part of the brain associated with learning, memory, and mood regulation. The hippocampus has been specifically implicated as a site for depression.3 Environmental factors, especially nutrition and physical activity, have been shown to reduce or increase through neurogenesis the size of the hippocampus.4 This study shows that just four years in the sixth decade makes a significant difference in the size of the hippocampus, depending on diet.
I recently read an amazing book, The Story of the Human Body, by the Harvard evolutionary biologist Daniel Lieberman.5 Lieberman traces the development of humans from the chimpanzee through the hominoids to our long hunter-gatherer period. He then describes the impact of the agrarian and industrial ages on our bodies and our health. The impact has been mostly negative. Sure, we are living longer than ever (for now), but we have a multitude of diseases not known to the animal kingdom. Most importantly, we have a growing epidemic of cognitive impairment and dementia.
Nutrition may have a preeminent role in the health of our brains. The emergence of understanding the gut microbiome in brain health has been presented in Internal Medicine Alert recently.6 Inflammation appears to be the common denominator in most chronic diseases involving the body and mind. Unhealthy foods induce inflammation in the body, something that deserves much more attention in our social policies, public health, and medical practice.
Heyward FD, et al. Adult mice maintained on a high-fat diet exhibit object location memory deficits and reduced hippocampal SIRT 1 gene expression. Neurobiol Learn Mem 2012;98:25-32.
Morrison CD, et al. High fat diet increases hippocampal oxidative stress and cognitive impairment in aged mice: Implications for decreased Nrf2 signaling. J Neurochem 2010;114:1581-1589.
Sapolsky RM. Glucocorticoids and hippocampal atrophy in neuropsychiatric disorders. Arch Gen Psychiatry 2000;57:925-935.
Das S, Basu A. Inflammation: A new candidate in modulating adult neurogenesis. J Neurosci Res 2008;86:1199-1208.
Lieberman DE. The Story of the Human Body: Evolution, Health and Disease. New York: Pantheon Books, 2013.
Scherger JE. You are what you feed your gut microbiome. Internal Medicine Alert 2015;37:121-122.