So, for example, the quality of adolescents’ diets is repeatedly related to their depressive symptoms, independently of family income, education, poor family functioning, family conflict, dieting behaviors, and the like. Similarly, the quality of women’s diets during pregnancy, as well as children’s diets in the first years of life, is also related to the children’s emotional health. This is very important to understand, as half of all mental disorders start before the age of 14 years; our findings point to diet as a key modifiable risk factor and a target for prevention.
At the other end of life, diet is increasingly recognized as a factor of importance in the risk for dementia, and we have shown that diet quality is clearly linked to hippocampal volumes in older adults, further supporting this association between diet and brain health. All of these very extensive observational data are supported by equally extensive animal studies, showing that diet influences key biological pathways relevant to the genesis of mental disorders, such as the immune system, brain plasticity, gene expression, the stress response system, and–very importantly–the microbiome-gut-brain axis. Finally, we have just published the first randomized controlled trial to show that dietary improvement, supported by a clinical dietitian, is efficacious in the treatment of major depression.
Psychiatry Advisor: What are the relevant treatment implications for mental health clinicians?
Dr Jacka: The quality of mental health patients’ diets, as well as their physical activity, sleep, and smoking habits are of great clinical relevance to their treatment outcomes and should not be considered as merely optional extras. If unsure about dietary recommendations, refer the patient to a dietitian. However, a detailed understanding of nutrition is not necessary to make basic and useful recommendations to consume food in line with the national dietary guidelines. We also believe that taking a “gut-focused” approach to dietary recommendations, focusing on increasing the intake of plant foods high in fiber and polyphenols, as well as healthy mono- and polyunsaturated fats from avocados, nuts, olive oil, and fish, may make it easier for people to understand and achieve a healthy diet.
Psychiatry Advisor: Can you describe your recent intervention study?
Dr Jacka: Our SMILES study recruited adults with major depressive disorder and randomly assigned them to either face-to-face social support, which is known to be helpful for those with depression and which acted as an active control condition, or to dietary support with a clinical dietitian over a 12-week period. The dietary condition comprised support from the dietitian in line with their standard clinical practices to increase the intake of healthful foods and to decrease the intake of “extras” (unhealthy foods).
The results showed a very large improvement in depressive symptoms in those in the dietary support group compared with more minimal improvements in the social support group. Indeed, roughly one-third of those in the dietary group were deemed to be in remission at the end of the study compared with 8% in the social support group.
Importantly, the degree of dietary improvement correlated closely with the degree of improvement in depressive symptoms. Our new economic evaluation also tells us that this was a highly cost-effective approach to treating depression, targeting overall health and resulting in lower societal and healthcare costs. The cost of our recommended diet was also cheaper than the unhealthy diets of participants at the start of the study, pointing to the fact that healthy diets do not need to be more expensive than unhealthy ones.
Psychiatry Advisor: What are some other exciting areas of emerging work in nutritional psychiatry, and what should be the focus of future research?
Dr Jacka: A rapidly developing body of evidence tells us that many of the key pathways influencing the risk for mental disorders, such as inflammation and oxidative stress, neurotrophins and brain plasticity, the stress response system, and gene expression, appear to be–to a certain extent, at least – under the control of gut microbiota. Recognizing that diet is the most important variable influencing gut microbiota, and that gut microbiota respond to dietary change within days, we are now focusing much of our research attention on this topic. In 2016 we set up the Food & Mood Centre at Deakin University, so people can head to the website and Facebook page to find out more about what we are doing there and to read about the work we have already done.
The ISNPR was founded in 2013, and we have just convened the first major international conference in Bethesda, Maryland in the middle of this year. Our next conference will be in 2019, likely in Europe, so clinicians with an interest in this topic can peruse the website and Facebook page for more information. New members are welcome.
The key point to remember is that an unhealthy diet is the leading contributor to premature death in middle- and high-income countries (second globally), while mental disorders impose the highest burden of disability worldwide. The fact that these two major causes of disability, suffering, and early death are closely linked has large implications for public health, as well as prevention and treatment. Given that so many factors that influence the risk for mental disorders, such as early life stress and trauma, social disadvantage and inequality, and genetic inheritance, are not readily modifiable, the identification of factors that are highly modifiable, such as diet, points to the importance of focusing on such factors in efforts to prevent mental disorders from developing in the first place.
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