What Is the Relationship Between Food and Mood?

SPEAKING OF LIFESTYLE PSYCHIATRY

“Speaking of Lifestyle Psychiatry” is an interview series with prominent researchers and clinicians who have made meaningful contributions to understanding the role of lifestyle interventions in mental health care. As this field continues to grow and evolve, the goal of this series is to facilitate a critical discussion of research methods and existing evidence, as well as highlight any evidence-based, practical interventions clinicians can utilize presently.

Felice Jacka, OAM, PhD, is a distinguished professor at Deakin University and is internationally recognized as a leader in the rapidly developing field of nutritional psychiatry. She is the founder and immediate-past president of the International Society for Nutritional Psychiatry Research (ISNPR). She is also the founder and director of the Food & Mood Centre at Deakin University. Jacka is a Clarivate Highly Cited Researcher (2020-24), putting her in the top 0.1% of scientists worldwide. In addition to academic papers, she has published 2 books: Brain Changer and There’s a Zoo in my Poo. In 2021, she was awarded the Medal of the Order of Australia (Queen’s honor) for her contributions to nutritional psychiatry.

Alli Young, MD: I would love to start at the beginning of your career. I read both of your books, and I know from Brain Changer, that your path to focusing on nutritional psychiatry was not exactly linear. What is your background, and how did you get involved in the type of work you do now?

Felice Jacka, OAM, PhD: Yes, so I had a very nonconventional background with quite an interesting family. They were naturopaths, so they had all sorts of strange ideas about health and conventional medicine. But one thing that was useful that I gleaned from their paradigm was that food is fundamental to health.

I eventually pursued art, but, in my 30s, because of my own experience with common mental disorders—depression and anxiety—I became interested in psychology. I went back to university to study psychology without any sort of science background at all. But while I was doing it, I realized that I was more interested in statistics and in the brain than I was in counseling, and I made my way to a newly established psychiatric research unit.

When I started working there as a research assistant, I quickly realized that there was not proper investigation of the potential role of diet and nutrition regarding mental and brain health. Unlike cardiology or cancer, or many other fields, where the influence on diet on these disease manifestations was well established, there was nothing like that in psychiatry. There is this paradigm of mind and body, and there was not much interest at that time in anything that happened below the neck.

Young: How did you get started on this research given the field had so little interest in the topic at that time?

Jacka: At that time, in the early 2000s, there was an increasing understanding that the immune system was involved in mental and brain health in a bidirectional way; this new field was called psychoneuroimmunology. Also, emerging research on the hippocampus suggested that it could generate new neurons, challenging the previous belief that the brain only lost neurons throughout life. It was noticed that this area of the brain, involved in learning and memory, is smaller on average in people who have clinical disorders and can grow again as people are successfully treated.

There were also animal studies at University of California, Los Angeles that showed exposure to dietary interventions, whether positive or otherwise, would have a very notable impact on the expression of proteins that grew the neurons as well as the size and the function of the hippocampus. So, there were starting to be these hints that there were all these mechanistic pathways, influenced by diet, that could contribute to mental disorders.

Young: Even though there was not much evidence in psychiatry, it seems there was starting to be interest and some evidence for diet’s impact on the brain in general. How did you translate these more mechanistic findings into psychiatric research?

Jacka: At that time, I was mainly focusing on depression. I had been learning about epidemiology as an undergrad and early postgrad, and I proposed doing a research study for my PhD that looked at the link between diet quality and clinically assessed mental disorders. Everyone thought I was a bit nuts, but they said, “Sure, why not? Go ahead.” I was working within this big epidemiological study that was doing psychiatric assessments that also had very good long-term data on dietary intake, plus all those other factors that we must consider, like socioeconomic status, income, other health behaviors, and body weight. I did that over 4 long years. It was a big study, including doing psychiatric assessments on about 700 individuals. Then I found pretty much what I expected to find: diet quality was inversely related to the prevalence of clinical major depressive disorder (MDD) and clinical anxiety disorders independent of all those other factors that I mentioned.¹

I think amusingly, when you look back, it was considered such a novel and important finding that it was accepted by and featured on the cover of the American Journal of Psychiatry and nominated by Medscape Psychiatry as the most important study in psychiatry research in 2010. That was kind of big news, and it allowed me to work with different groups around the world very rapidly. These groups had already collected a lot of data, including on diet and mental health, but they had not thought to put it together that way. I was able to develop the evidence base from the observational data quickly.

Young: What was the first randomized study you completed on this topic?

Jacka: The SMILES trial.² This was really the first randomized controlled trial to show diet quality had a significant impact on people with MDD. In this study, we randomly assigned people with moderate to severe MDD to an active control of social support or dietary support with a dietician. Most of the participants had been sick for a long time and were also on medication.

At the end of 3 months, we really did not expect to see anything because we had far fewer people recruited into the trial than we hoped to get. But surprisingly, we saw a big difference between the 2 groups, with a full third of the dietary group going on to achieve full remission of their depression. We saw a very clear correlation between the degree to which people improved their diet quality and the degree to which their depression improved. It was also a highly cost-effective intervention.³ We did a very detailed cost analysis of the diet we were advocating for and established in the study. It was less expensive than the typical diet, heavy in junk foods, that people were eating when they came into the study. Importantly to me, many of those in the dietary group went on to make substantial changes to their lifestyle and continued to experience benefit even after the study ended.

Since that trial, there have been many other observational studies around the world as well as other trials with similar study designs as our SMILES trials, that all have findings similar to ours. We repeatedly see diets lower in ultra processed foods and higher in whole foods like vegetables, legumes, whole grains, fish, and unprocessed red meats, are linked to reduced prevalence and a reduced risk of developing depression.

Young: A large portion of the studies in nutritional psychiatry have been on depression. Is that just because depression is so common, so much more well studied, or is there something particular about depression that it makes it more responsive to dietary interventions than other mental disorders?

Jacka: Nutritional psychiatry is a relatively new discipline. The first study done looking at diet in relation to clinical mood and anxiety disorders was the study we did in 2010. We looked at those areas because they were the data available to me. There is definitely a need to do more work and push into other areas.

I think with major depression, it is possible we know more about it. It is something that very clearly has physiological correlates like elevated inflammatory markers. There has also been research into the stress response system and the brain-gut axis. Anxiety also seems responsive to diet quality, but it has been studied less.

I work closely with groups internationally who have pioneered the use of lifestyle approaches to support people with psychosis because both the medications as well as the psychotic disorders themselves seem to come with dysregulation of glucose and lipid metabolism, which profoundly affects the physical health and lifespan of those with serious mental disorders. Joseph Firth, PhD, has pioneered a lot of exercise and serious mental disorders research, along with Brendon Stubbs, PhD, although they have also produced a lot of research in depression. It is not just research but bringing it into practice for people with any mental disorders to benefit from. There is a big Lancet Psychiatry Commission Report on the physical health of people with mental disorders that was led by Firth, making the strong case that we need to do far better in addressing the health of the whole person affected by mental illness—not just their mental health symptoms. We know that people with serious mental disorders die on average 20 years before someone without that disorder.⁴ It is not just because of suicide; it is because of cardiometabolic illness. We know that lifestyle approaches, including diet, are important to support the health of those with mental disorders. But what has not been looked at enough, especially in psychosis, is the impact on psychiatric symptoms and psychiatric functioning. There are several reasons for that, but part of it is the recency of this area of study.

What we are doing now is the first pilot of a blinded study. People will be provided all their food and not know which diet they are on. I think proper blinding needs to happen next. It is very hard to blind diet.

Young: Blinding tends to be an issue for research on lifestyle interventions in general. The attempt to blind diet sounds interesting. So, they are not verbally told what diet they are on? But it is possible they can look in there and know the types of food they are being provided?

Jacka: Unfortunately, as usual for this field, it is an underfunded study. It is for about 3 weeks and the meals are delivered to them. And, for example, a standard Australian diet would have things like pasta. You can have healthy pasta that has lots of vegetables hidden in it and olive oils, or you can have pasta with just tomato sauce and cheese. They will just know they are getting pasta that meal. So, in a sense, the diet type is blinded. A member of our team, Heidi Staudacher, PhD, pioneered the development of these sham diets. She is one of the leaders in disorders of gut-brain interactions.

There is other interesting research we are doing with blinding. We recently published a study of fermented dairy and a placebo version that the company developed for us. This study was in healthy women and looked at the size and connectivity of their hippocampus on MRI scans, showing that women consuming the fermented dairy product, compared with placebo, had a larger hippocampus and various other potentially beneficial changes in their brains.⁵

We also recently published a small study where we did a preliminary test of the hypothesis that ultra processed foods, even when nutritionally balanced, are not the same as real foods.⁶ For this study, we used these very low energy meal replacement shakes and bars that are used for people needing to lose weight. They are low in sugar, they have added fiber, they have added vitamins and minerals, and are considered nutritionally balanced. We compared these with a very low energy diet with the same calories, but made up of real whole foods, mainly vegetables and legumes. This was a 3-week intervention in women living with obesity, and they were provided all their food. What we saw was the women who got the meal replacement items had decreased diversity in their gut microbiome. We saw the opposite in women who were given the whole foods. This could be a key mechanism for why ultra processed foods have such a differential impact on weight and health, but we need a lot more research to develop this further.

Young: Interesting! You mention diet quality a lot, and diet quality relates both to what someone is eating as well as what they are not eating. Is there a sense based on the research of what is more important? Is it someone eating nutritious stuff or limiting the bad stuff?

Jacka: The observational literature shows they both have an impact independent of each other. If you do not have enough good stuff, or if you are eating a lot of bad stuff, both are independently linked to worse mental health. So far, the observational literature shows they are roughly equivalent.

In the SMILES trial, the individuals in the dietary group were encouraged to increase vegetables, fruits, legumes, fish, and olive oil. They were also encouraged to drop what we call “discretionary foods.” These are nonessential foods, like treats. The participants in the dietary group had an average 7-point reduction on their MADRS rating scale by improving the foods they ate. But, for every 10% reduction in ultra processed foods, there was an extra reduction in MADRS score of about 2.5 points. So, it seemed dropping the junk food really drove the big reduction. This needs to be replicated. But I suspect, in the short term at least, you will get more bang for your buck by dropping the junk.

Young: And of course, by filling up less on junk, you may wind up relying more on nutritious foods to feel full.

Jacka: You would hope so!

Young: One thing I think has been tricky in this field are the public diet wars. There is so much information and misinformation in the public as well as people that seem very invested in one type of diet over another, whether it is keto, or gluten-free, or plant-based. Based on the research, what are the most powerful dietary recommendations to impact depression (since that is the most well-researched disorder)?

Jacka: Oh, that is easy: it is a Mediterranean style diet. That has been the one that has been used in all the trials and has shown to have a very high level of efficacy. A traditional Mediterranean diet contains a lot of vegetables, wild greens, fermented foods, fish, olive oils, nuts, seeds, and legumes. In terms of proteins, it is smaller amounts of meats. Not a massive steak, but smaller portions of that. That is where the evidence is.

Young: Is any other diet type backed by research?

Jacka: There is some evidence for keto diets, which is mostly limited to case studies. The trouble is, when people talk about keto, most of them have no idea what it actually is. Most of the people attempting it in the world do not achieve ketosis. Some of these people damage their health eating huge amounts of animal proteins and not enough other nutrients. To do it correctly, a ketogenic diet is very strict and limited and should be medically supervised. Most of the interest and focus on keto diets is in bipolar disorders. But there are research projects underway, and we have been running a pilot study of a ketogenic diet.

I find it interesting because ketogenic diets are kind of opposite what the microbiome needs. We have coevolved with the microbiome, and it is critical to our health. Their primary role is to break down the components of food that our human enzymes cannot break down, which is largely fiber. Fiber is found in starchy vegetables, fruits, and legumes. A ketogenic diet does not give those microbes the food they need to do what they are supposed to do. That is where our understanding is at the moment. Now, we may find that if you had a very healthy form of a ketogenic diet, your microbes can adapt, which is the sort of thing we are testing in our pilot study. We have also just published a very large review of the evidence regarding the impact of different dietary interventions on the gut microbiome, and it very clearly supports diets high in plant and whole foods and low in western foods. It suggests equivocal impacts of ketogenic and other restrictive diets.

Young: In terms of implementation, it seems like a Mediterranean diet is less restrictive and can be adapted to fit many different dietary preferences.

Jacka: Yeah. It seems the traditional diets from all over the world have at their heart what we could call a version of a Mediterranean diet—a diet high in a diverse range of plant foods and low in junk.

Young: We have talked a lot today about overall diet quality and diet type, but there has also been a focus in the field on micronutrients. In the public, you hear lots of big recommendations on micronutrients, like vitamin D and vitamin B complex. What does the research say about micronutrients, and/or the importance of micronutrients compared with overall, whole diet?

Jacka: There is some very good meta-analyses of the research into supplementation in psychiatry, and what they tell us is that the evidence for nutritional supplementation is pretty limited and weak.

It is not to say these micronutrients are not important, but the quality of the supplements can vary, and the fundamental thing is that nutrients taken in a pill form are not food. They are not comparable. There is some evidence that some of these nutritional supplements may be helpful to people as adjunctive treatment, particularly in groups that are very deficient nutritionally.

Diet is so complex. When we just think of phytochemicals, these secondary plant metabolites that people often think of as antioxidants, there are so many of them we do not know. The latest estimate is as many as 150,000. Then they interact with each other in ways we do not understand. It is mind-bogglingly complex, much like the brain in general.

But it is hard to get the funding to investigate these complexities. I think peer reviewers seem to think “oh, we already know that bad food is not good for your brain,” but we have only scratched the service, and the rigorous scientific evidence needs to be there.

Young: For sure, and I think the evidence needs to be there for a couple reasons. One, to definitely know what sorts of recommendations to make regarding different diet types and supplements, we need to know. But the other things is, without the evidence, people view these interventions as a “softer science.” If people do not put the money into studying this, it unfortunately always seems inferior to other interventions.

Jacka: Yes. It seems inferior to pharmaceuticals, which are just so much simpler to test.

Young: Exactly. And diet change is something accessible to everybody. There is a huge issue all over the world regarding access to care. I would hope there would be great interest in any intervention that seems promising and is easy to access, whether for prevention, treatment, or adjunct treatment.

Jacka: Yes, and there are ways to eat well affordably. Frozen vegetables are cheap and are great. Tinned beans and tinned fish as well as dried beans, lentils, and chickpeas are also cheap, and they do not go to waste quickly. And you do not have to focus on organic. At the moment, many people are getting the bare minimum of plant food. We have got to start somewhere.

Young: I have noticed, in Australia, lifestyle interventions are now considered a first line treatment based on recommendations. How does this work in practice?

Jacka: It is really challenging, and the actual health services and the delivery is a big topic of interest. First, we need to up-skill psychiatrists and mental health clinicians, so that they at least know what the evidence is. Give them very simple tools to start. Even just to have the conversation: What do you think about your diet? What does your breakfast or lunch or dinner look like? What is healthy food to you? These sort of conversations. Same with movement.

But ideally, for implementation, we really need to think more about multidisciplinary practices. Relatively recently, we published a very important noninferiority study in one of the Lancet journals. It is called the CALM Trial, led by Professor Adrienne O'Neil on my team.⁸ It was run during COVID, via Zoom, because in Australia, and particularly in Victoria, where I live, we had long lockdowns. We randomly assigned people coming through the mental health services who had elevated psychological distress to get either lifestyle support delivered by a clinical dietician and an exercise physiologist in a group setting or psychological support from a psychologist delivering CBT in a group setting. At 3 months, there was no difference in the groups. Both groups improved. Put simply, lifestyle support was noninferior to psychological support.

Now, we are doing a large national trial as we speak. This trial is in primary care, where people often go first and are flagged through a PHQ-9 questionnaire. If flagged, they get a full assessment, and if they meet criteria for a depressive episode, they are offered the opportunity to participate in this trial. They will be randomized to either a lifestyle-based treatment or to psychological therapy. Again, this is a noninferiority trial and it is meant to inform clinical care. In Australia, we have Medicare, and the government wants to know, with this mental health crisis, what are we going to do about mental health workforce? It may be that we can actually bring in allied health workforce. Dietitians and exercise physiologists can be a part of that mental health workforce. There may be room for shared care or group-based care. There are lots of different models that will be possible once we have the evidence one way or another on whether lifestyle support is as effective.

Young: That is an important study. Not only for access to care, but also to appeal to different people. I notice some people, whether because stigma or something else, just are not interested in psychotherapy. It is helpful for them to have other options to improve their mental health. These lifestyle interventions may also be more transdiagnostic, if there is a physical health issue or something else going on.

Jacka: Absolutely. It is a win-win. This idea that somehow mental health or illness exists in the head, and then physical health exists in the body, is just so clearly outdated. We are such a complex, tightly integrated system. When you address the foundation of health, which is lifestyle, you affect every one of those systems.

Young: Well said. Can you recommend any resources if people are interested in learning more about how diet relates to mental health? Especially for a clinician who may have to stick with 15-minute visits. Are there any resources you can point to that provide simple things that can be implemented in shorter visits?

Jacka: Yes. Because this is an issue—even as we increasingly recognize the importance of food, it is a challenge because psychiatrists around the world generally have about 2 hours of training in nutrition throughout all their schooling. So, we created the Food Mood Centre and Academy. Firstly, the Food and Mood Centre website (https://foodandmoodcentre.com.au/) has lots of resources and information on it. But then, as part of that website, there is also the link to the Food and Mood Academy (https://foodandmoodcentre.com.au/academy/). There, you can get training. There is the free online course, which is designed for the general public. Then there is Nutri-Psyche, which is designed for psychiatrists, designed with our Royal Australian New Zealand College of Psychiatrists. Lastly, there is Life and Mind, which is intended for general practitioners and people in health care settings. They are all rigorously evidence-based and not-for-profit.

Young: Those sound great. Thank you so much. It was such a pleasure to meet you, and to be able to have this conversation with you. Any closing thoughts?

Jacka: Oh, it was a pleasure to talk to you too, Alli! I think the idea that you can influence your mental and brain health with food is awesome because it means there is potentially things we can control. There are so many things that affect mental and brain health that are just not in people’s control. Trauma, growing up in poverty, all these things. So, to at least have something that can effectively improve mental and physical health, is really exciting. It is not about worrying about your weight or your body; it is not a wellness fad; it is a foundation to human health.

Dr Young is an adult psychiatrist in private practice and affiliate professor of psychiatry at FAU Charles E. Schmidt College of Medicine. Additionally, Dr Young is a medical reviewer and contributor at Everyday Health.

The opinions expressed in the interviews are those of the participants and do not necessarily reflect the opinions of Psychiatric Times.

References

1. Jacka FN, Pasco JA, Mykletun A, et al. Association of Western and traditional diets with depression and anxiety in women. Am J Psychiatry. 2010;167(3):305-311.

2. Jacka FN, O’Neil A, Opie R, et al. A randomized controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial). BMC Med. 2017;15(1):23.

3. Chatterton ML, Mihalopoulos C, O’Neil A, et al. Economic evaluation of a dietary intervention for adults with major depression (the”SMILES” trial). BMC Public Health. 2018;18(1):599.

4. Firth J, Siddiqi N, Koyanagi A, et al. The Lancet Psychiatry Commission: a blueprint for protecting physical health in people with mental illness. The Lancet Psychiatry Commission. 2019;6(8):675-712.

5. Marx W, Suo C, Dissanayaka T, et al. Effects of a probiotic fermented dairy product on hippocampal metabolites, structure and function: an 8-week randomized, placebo-controlled trial in healthy women. Gut. 2025;75(3):e335398.

6. Lane MM, McGuinness AJ, Mohebbi M, et al. Food- vs. supplement-based very-low-energy diets and gut microbiome composition in women with high body mass index: a randomized controlled trial. Cell Reports Medicine. 2025;6:102417.

7. Aslam H, Trakman G, Dissanayake T, et al. Dietary interventions and the gut microbiota: a systematic literature review of 80 controlled clinical trials. J Transl Med. 2026;24(1):39.

8. O’Neil A, Perez J, Young LM, et al. Clinical and cost-effectiveness of remote-delivered, online lifestyle therapy versus psychotherapy for reducing depression: results from the CALM non-inferiority, randomised trial. Lancet Reg Health West Pac. 2024;49:101142.