Poor diet quality can increase the risk for certain mental disorders, including depression and anxiety. That was the message delivered by Felice Jacka, Ph.D., in a March 20 talk for the NIEHS Keystone Science Lecture Seminar Series.
“We were thrilled to have Dr. Jacka visit us from Melbourne,” said Jonathan Hollander, Ph.D., who introduced Jacka’s talk. “Her work touches on several growing research areas at our institute, including the impact of the environment on the gut microbiome, immune system, and mental health.” The microbiome refers to the total population of microbes living in and on the body.
Jacka addressed epidemiological data linking diet with mental disorders, new intervention data, and molecular data that identify the underlying biological mechanisms. These include pathways related to oxidative stress and inflammation, as well as brain physiology and the varieties of microbes in the gut. Jacka also participated in a workshop on how exposures might contribute to psychiatric disorders (see related story).
“My research program considers things from the meta perspective — what are the population health implications, the big picture, and the context,” said Jacka, director of the Food and Mood Centre at Deakin University in Australia. “But we’re focusing now on the mechanisms and getting down to the very small, and that’s when we come into the microbiome.”
The gut microbiome encompasses all of the microorganisms that reside in the digestive tract. Previous studies have found that it regulates many biological processes, such as metabolism, immune function, and mood. According to Jacka, a healthy microbiome has high diversity of microorganisms, and diversity is driven largely by diet.
Her research has found that a poor diet — whether high in processed foods, fat, and sugar, or low in nutrient-dense foods — is associated with reduced volume of the hippocampus, the part of the brain that regulates learning and memory, as well as regulating effects on mood.
A poor diet also appears to increase the production of free radicals and inflammatory molecules, and it also reduces the expression of brain-derived neurotrophic factor, a protein that protects brain cells and promotes their growth.
“We’ve known for many years that dietary patterns influence our risk for chronic disease,” said Jacka. “We know that depression is highly comorbid with these conditions, and we suspect common underlying pathways, particularly around immune dysfunction, that are linked with diet. Now, we know that diet and mental health are linked.”
Public health intervention
To lower one’s risk for both physical and mental diseases, Jacka recommended regularly eating a healthful diet of whole and unprocessed foods, and the earlier these habits start, the better. Jacka said half of all mental disorders develop before adolescence, and dietary intervention could start as early as pregnancy.
“Knowing that the vertical transmission of microbiota happens during pregnancy and delivery, it’s clear that a healthy microbiota in the mother is essential for the baby to have a healthy microbiome,” said Jacka. “If you improve maternal diet, you are likely to get improved mental health in mothers [and] improved mental health in children.”
Jacka’s research suggests that both mental health and the composition of gut microbiota improve rapidly after modifying one’s diet. Implementing such dietary changes, as well as identifying more molecular pathways involved in the role of diet and mental health, could lead to public health interventions.
“You have to think about the public health implications of our food system as it stands and what’s normalized,” said Jacka. “What are the implications for how we are living now, particularly in the west, and what does that mean for our future and that of our children?”
Jacka FN, O'Neil A, Opie R, Itsiopoulos C, Cotton S, Mohebbi M, Castle D, Dash S, Mihalopoulos C, Chatterton ML, Brazionis L, Dean OM, Hodge AM, Berk M. 2017. A randomised controlled trial of dietary improvement for adults with major depression (the 'SMILES' trial). BMC Med 15(1):23.
Jacka FN, Cherbuin N, Anstey KJ, Sachdev P, Butterworth P. 2015. Western diet is associated with a smaller hippocampus: a longitudinal investigation. BMC Med 13:215.
Slyepchenko A, Maes M, Jacka FN, Kohler CA, Barichello T, McIntyre RS, Berk M, Grande I, Foster JA, Vieta E, Carvalho AF. 2017. Gut microbiota, bacterial translocation, and interactions with diet: pathophysiological links between major depressive disorder and non-communicable medical comorbidities. Psychother Psychosom 86(1):31–46.
(Emily Mesev is a postbaccalaureate Intramural Research and Training Award fellow in the NIEHS Intracellular Regulation Group.)