THE MICROBIOME SUMMIT : Impacts of Sanitizing Our World

Findings on the Impact of Diet on Depression

Dr. Felice Jacka, PhD

Deakin University

Overview
Transcript

Overview

There’s no doubt that diet plays a role in physical health, but emerging science is uncovering the role of diet in mental health. Dr. Felice Jacka is a leader in the field of nutritional psychiatry, and has led studies to help answer answer the question, if I have major depressive disorder and I change my diet – will it help? In this interview, Dr. Jacka will share findings from numerous studies that have linked diet and mental health – beyond simply looking at isolated nutrients. This is research that will ultimately change the way that we approach the treatment of mental health.

Transcript

Tracey:
We’re here at the University of Toronto with Doctor Felice Jacka. She has her PhD in psychiatric epidemiology, she is an associate professor at Deacon University in Australia, and she’s joining us here today. Welcome.
Felice:
Thank you, thanks for having me.
Tracey:
Can you tell us about some of the projects that you’re involved in, and what you are up to in your career right now?
Felice:
Sure. Well, I head up the International Society for Nutritional Psychiatry Research. And in Australia, I’m head of the Alliance For The Prevention Of Mental Disorders, and of course there’s some real overlap there.
Tracey:
So what is happening in the area of nutritional psychiatry?
Felice:
Well, look, it’s a really interesting and very fast-moving field, as the rest of medicine. It’s a field that’s relatively new. It’s really only since end of 2009, beginning of 2010, that we’ve had some really good-quality epidemiological research that looks at the whole of diet and its relationship to mental health. So, prior to that there was a number of studies that really looked at single nutrients, looked at single foods, such as fish intake, and some supplement studies. Some of them were good-quality studies, others not so much. And then the field of nutritional psychiatry and nutritional epidemiology, in general, has really moved away from looking at just single nutrients, because, of course, we don’t eat just single nutrients, and similarly, single food components. To look more at the whole of diet and diet quality is a general concept, and we were really the first to look at this against mental health, because we’ve known for a long time, of course, that the quality of people’s diets is related to their physical health, but we were very interested in looking at it against mental health.
And so we’ve started really doing that in the last few years, and now the whole field has really come a very long way, and there’s been a lot of work done in the area, and a lot of very interesting new evidence has come to light.
Tracey:
Yes. Can you tell us about some of that research that is coming to light? I mean, we’ve always thought that there was a disconnect between mental health and what you ate. I mean, nobody ever made those connections, and here you are- how did you get interested in it? And, tell us what’s happening.
Felice:
Well, it was really fascinating to me when I first came into psychiatry research, which was relatively late in my career. I started to look at, you know, epidemiology as a discipline, and psychiatric epidemiology in particular, I was fascinated to realize that there really was no credible data looking at diet quality and mental health, and that was interesting to me because what we’d begun to really understand in psychiatry was that that old-fashioned-mind-body dichotomy didn’t really hold true, and that things such as depression, in particular, they were really whole-body disorders, and they involved the immune system in particular, and many aspects of physical functioning that were also involved in things like cardiovascular disease, and diabetes, and obesity. And we also knew, of course, that those things are very closely linked with depression, in particular. So, there’s bidirectional relationships there. If you’re overweight you’re more likely to have depression.
But similarly, if you’re depressed you’re more likely to actually put on body weight. Heart disease, similarly, if you have heart disease you’re more likely to be depressed, and if you’re depressed it’s actually a risk factor for heart disease. So there’s underlying pathophysiology there…
Tracey:
Absolutely.
Felice:
… and much of it relates to the immune system. And, of course, diet really affects the immune system. So, that was really the starting point. At the same time, there were a number of really important and very interesting studies coming out of UCLA. A colleague of mine and their group, they were looking at aspects of brain plasticity and the growth of new neurons in the brain, and looking at the impact of food and aspects of food on neuronal growth, and showing that diet seemed to be really important for brain plasticity in these areas of the brain that we know are really important in mental health, as well as in learning and memory. So these two things, you know, really got me thinking. And so, when it came time to consider a PhD, I told my potential supervisor that I really wanted to look at diet quality and mental disorders. And there was a bit of scoffing and a bit of, “Well, you can do that, but I don’t think you’ll find anything.”
Tracey:
Yeah.
Felice:
And quite a bit of skepticism from many people.
Tracey:
I can imagine.
Felice:
But I went ahead and did my PhD and figured out how to capture that information about diet and nutrition. And then we did structured psychiatric clinical interviews on more than a thousand women, right across the age range, very representative of the community. And then we basically put those two things together. We looked at the quality of their diets, and we looked at that in a number of different ways. We looked at their mental health, and then we took into account, of course, things that could explain the link between the two. So, you know, their socioeconomic status, their level of education, that sort of thing.
Physical activity, BMI, etcetera. And then we saw this very, very striking link between the two. So women who had better diet quality were less likely to have what we call common mental disorders; that’s depressive and anxiety disorders. Those who had higher scores on what we call this western dietary pattern, this unhealthy, processed food dietary pattern, they were more likely to have these disorders. And I was really fortunate, because that was then published on the front cover of the American Journal of Psychiatry, and it had quite an impact on the field.
Tracey:
Amazing. What year was that?
Felice:
That was 2010. But you know, there’s this lovely synchronicity, because then there were two other studies published at almost exactly the same time, one in what was Archives of General Psychiatry, and one in the British Journal Of Psychiatry. So they were the three leading journals in psychiatry research at the time, and the other two studies showed very similar things. One looked at levels of adherence to a Mediterranean diet, and showed that seemed to be associated with a reduced risk of depression, and the other looked at, in Britain, at a cohort of middle-aged public servants, and followed them over time, and found, again, similar to what we found, that those with healthier diets were less likely to develop depression, and those with unhealthier diets were more likely to develop depression. And in those particular studies, of course, they took into account things like what we call reverse causality, because we know that if you’re depressed it has an impact on your appetite and what you want to eat. So, people will often want to eat sweet, sugary foods, because they actually do actually comfort you. They bring down your stress response. But that reverse causality didn’t explain the associations that we saw. So since then, there’s been a host of studies done all over the world, the U.K., the U.S., Australia, but also Asia. And then, I was able to do this in adolescence, which is really important to consider because half of all mental disorders start before the age of 14. And because I’ve always got my prevention hat on, you’re looking for modifiable factors that you can change to prevent disease. And we showed, very convincingly, that the quality of adolescents’ diets was related to their mental health, and their depression as well.
And then we went back even further, and we had funding from a large American philanthropic organization to go and look at, really, right at the start of life. So, there’s this area of medicine that we call DOHAD, Developmental Origins of Health and Disease, and that’s really focused on this idea that what nutritional exposures that you have in early life, not just nutrition, but early life exposures, affect your risk for disease over your life course. And it’s already been shown pretty convincingly that early life nutrition, what mum eats when she’s pregnant, what you eat in the first few years, is linked to your risk for physical health outcomes, such as heart disease. We wanted to know whether this was also true for mental health. So, we were able to look at data from more than 23,000 mothers and their children. This is in Norway. We looked at mums’ diets when they were pregnant.
Tracey:
Right.
Felice:
In great detail. We looked at the kids’ diets over the first few years of their life.
Felice:
And then, so we looked at the quality of diet in mums and their children, and then we looked at the children’s trajectory of what we call internalizing and externalizing.And these are behavioural markers that tell us something about their vulnerability to mental disorder. So externalizing is, you know, tantrums, and anger, and aggression, and internalizing is sadness, and worry, and crying, and that sort of thing. And both of these are markers for vulnerability to depression and anxiety, in particular.
Tracey:
Interesting. So the temper tantrums in the terrible twos, are they normal or not?
Felice:
They are probably very normal and of course temperament comes into it as well. But what we saw was that there was a link between the dietary exposures and the children’s levels of these. And of course again, we take into account family functioning, SES, education all of these other factors that might influence, mother’s mental health in particular. But what we saw very clearly that mothers who had more junk or processed foods during their pregnancy, the children had higher levels of externalizing behaviours.
Tracey:
More temper tantrums.
Felice:
Yes. And then quite independent of that what the children ate seemed to be really important as well. So the children who had higher intakes of healthier foods and nutrient dense foods had lower levels of these behaviours and the kids who had higher intakes of the junk and processed foods had higher levels of internalizing and externalizing. So that was really interesting. It was telling us that the impact of early life nutrition is not just going to affect physical health, it may also be affecting mental health. Two other very large cohort studies have shown the same thing. So the big British ALSPAC study and another study in the Netherlands have also shown very similar things that the mothers’ diet seem to be linked to the childrens’ internalizing and externalizing. So that is a really important understanding and it makes total sense. Because if you look at the animal data where they feed pregnant mice or rats or non-human primates the junk food diet during pregnancy, it has quite pronounced impacts on a whole range of things that we know are related to the risk for mental disorder.
Tracey:
Absolutely. Now as I am listening to you, I am also a parent. I’m saying “Okay…”
Felice:
More things to feel guilty about.
Tracey:
Well what should be on the dinner plate? In an ideal world, what would you like to see on the dinner plate?
Felice:
What we have seen from all of the studies from all around the world and there have been many of them now, is that each country has its own version of a healthy diet. So a healthy diet in Norway looks a bit different than to one in Japan or Australia. So there are many forms of a healthy diet. But what they do at their base is higher intakes of plant food, vegetables, fruits, unprocessed foods, good quality whole foods. I really like that Michael Pollan saying which is really the simplest and easiest way to think about food which is “ Eat real food. Not too much, mostly plants. “
Tracey:
Right. And now you have done the research. So you’re able to tell us, and explain to the medical community now, that diet matters, that it matters what mothers are eating when they’re pregnant. It matters what their children are being fed. Because this, then, has an effect on mental health issues.
Felice:
Well, there’s two aspects to that, that I think are really important to understand. One is that because this is a relatively new area, to date, most of the scientific evidence that we have is coming from what we call observational studies. So, this is where the epidemiology comes in. So you collect information on people’s diets, you collect information on mental health, you put the two together, you’re using statistics, but correlation doesn’t mean causation. So you can look at the data and you’re saying, “Look, it’s making a pretty compelling story, it’s very consistent, there’s dose response relationships, etcetera, etcetera.” But without intervention studies, where you actually go in and conduct an experiment, and you manipulate diet to see what impact it has on mental health…
Tracey:
Right.
Felice:
…then you can’t say for sure that it’s causal. Certainly, there’s a host of experimental data in animals, but you know, people are not animals, animals are not people. So we really needed these intervention studies. Now, there’s one that’s been published, which I think is a very important study. This is from the very large PREDIMED study in Europe, which is the largest dietary intervention. In that study, they identified older adults who are at increased risk of having a heart attack, having a cardiac event. And what they did was they randomized them to one of three different dietary conditions. So, the control condition was this low-fat dietary advice, according to the American Heart Association. And then the other two dietary groups that you could go into were a different form of Mediterranean diet, which we know is a really healthy way to eat. One Mediterranean diet group was told to have more extra virgin olive oil; the other one was told to have more nuts, raw nuts. So, tree nuts, things like almonds and cashews and walnuts, etcetera.
Tracey:
Right.
Felice:
30 grams a day, which is about a handful.And then they followed those people over time, and what they were really interested in looking at was who went on to have a cardiac event, and they stopped the trial after a certain amount of time, because it was quite clear that those who’d been randomized to the Mediterranean dietary conditions were less likely to have a heart attack, and that very important finding was published in the New England Journal of Medicine.
Now, colleagues of mine got hold of the depression data that they had actually collected as part of that trial. They then asked everybody about whether or not they’d been diagnosed with depression. Now, to identify people who have never been depressed before at that end of their life, you usually need a very large sample of people because, as I said, most depression tends to manifest earlier in life. But in this case they only had about 4,000 people. We would normally say that you’d need many, many more than that to be able to test this hypothesis, that if you improve people’s diets it will result in a reduction in their risk for new depression.
Anyhow, they looked at the data, and they found that even though they had a much smaller sample size than they would have needed on paper, they saw a very strong trend wherein those in the Mediterranean diet groups, and particularly those who’d been told to have the nuts were less likely to develop a new depressive disorder. And for about half the sample who had Type 2 diabetes, it was clearly statistically significant. So, it was saying if you have Type 2 diabetes, and you’re an older adult, and you switch your diet so that it’s more like a traditional Mediterranean diet, which is, of course, lots of plant foods, fruit, whole grains, fish, olive oil, balsamic vinegar, all these healthful things, then you are less likely to develop depression. So that was very cool.
Tracey:
That is very cool. And what year was that study done?
Felice:
I think that was published 2014, I think.
Tracey:
Yeah. So this is all such new information.
Felice:
Very, very new.
Tracey:
So, is this shifting—are we moving into a new paradigm of understanding?
Felice:
Yes, well I think that this will come about, and probably, hopefully, quite soon, because the study that we’ve just done is, I guess, really the missing piece of the puzzle. So, that study—what we haven’t had up until now is a study that seeks to answer the question, “I’m depressed, should I improve my diet Will it help?”
We haven’t actually known that.
So, we were funded to run that study, the very first study that actually asked that question, and we started recruitment in 2012. We finished recruitment in 2015. It’s very tough to recruit people with major depressive disorder where you often just don’t want to get out of bed to go and see somebody weekly and fortnightly, and subject yourself to tests and questionnaires, etcetera. So, it was really tough to recruit for it. But what we did in this was we recruited people with major depressive disorder, very serious disorder, and we randomized them to two different groups, one of two different groups. And one group got what we called the friending, or social support. So we know that that’s really helpful for people with depression to just go and talk to someone. It’s not counselling, but it could be talking about the footy, their grandchildren, whatever. But the other group saw someone to the same schedule, but it was a clinical dietitian. And that clinical dietitian worked with them in a very gentle way to help them to improve their diet. It’s nothing about weight; weight doesn’t seem to come into this equation.
Tracey:
Yeah, that’s the interesting part.
Felice:
It is, it’s very interesting. Because the relationship between diet quality and weight is not as strong as you might think.
Tracey:
Yeah.
Felice:
So there’s many people who have a healthy diet but are heavier, and those, sometimes, who have very unhealthy diets but they’re lighter. And I think if you’re trying to change diet, people, unfortunately, really focus on weight as the outcome.
Now, we know it’s very difficult to lose weight once it’s on; the body does everything it can to hold onto weight. So, we think that we need to actually just ignore the weight thing, and just concentrate on increasing the quality of our diet. And that’s what the dietitian helped the participants to do, to increase their intake of vegetables, of fruits, of whole grains, of legumes, so your lentils and chickpeas, and beans, nuts, olive oil, fish, those sorts of things, but also reduce the intake of the foods that we know are really noxious to health, that are really noxious for your brain, for your gut microbiota, for your immune function, etcetera, which of course are the processed and take-away type foods. And so, what is incredibly exciting is that even though we didn’t get as many people as we’d hoped for, I really didn’t think that we would see a difference between the groups. We saw a huge difference.
Tracey:
What do you think is happening?
Felice:
We don’t know, but that’s part of what we’re hoping to try and find out. So, we’ve taken blood samples from these people and we’re going to be looking at levels of biomarkers that tell us something about their immune function tell us something about their gut health, that tell us something about their brain plasticity, just seeing whether any of those things change. Now, we may not have enough people to be able to tease that apart. We may not have sensitive enough markers to be able to see that sort of a change, but that’s one of the challenges, is to try and understand how it is that diet might be exerting its effect on mental health.
But the key thing about this study is that it tells us, for the first time, that this relationship is probably a causal one. It’s not just that we’ve seen that diet and mental health are related, but actually diet does exert an impact on mental health. And the reason that that’s important is absolutely critical. What we know from the latest global burden of disease statistics published at the end of last year in the Lancet is that unhealthy diet is the leading risk factor for early mortality around the world. It’s the leading—it’s not HIV, it’s not malaria. It’s unhealthy diet. But what many people don’t know is that mental and substance use disorders, particularly depression and anxiety, account for the leading global burden of disability. So, you’ve got the leading cause of early death, the leading cause of global disability, the fact the two are linked and diet, of course, is imminently modifiable has huge implications for public health, globally. For clinical care, for food policy.
You know, this is an absolutely critical understanding. And that’s why this trial is so important, because it’s saying this is a causal relationship. But it’s also saying if you’re a clinician, if you’re a GP sitting in your office, and you’re seeing people with depression all the time, if you’re a psychiatrist, etcetera we think it’s going to be really useful for people to actually get some dietetics advice, to maybe get a referral to go and see a dietician who will help them to improve their diet. And of course, it’s also going to benefit the comorbid disease that goes with depression, like heart disease, and diabetes, and obesity. So, it’s going to have a whole range of benefits. And we also think, from a public health perspective, that maybe people will pay a bit more attention. Because when you’re a young person and you’re really enjoying your shakes and your hamburgers, etcetera, and someone says, “Well, if you keep eating like that you may develop heart disease, you may develop cancer, you may develop diabetes,” for them it’s all off in the future.
Tracey:
Sure, they think they’re invincible.
Felice:
They’re invincible.
Felice:
If you say to them, “This is going to affect your mental health, and it’s going to affect your ability to learn, and remember, and study, like, your brain function,” then we think that that might have more of an impact on their behaviour.
Tracey:
I think that’s so important. Thank you so much.
Felice:
It’s a pleasure.