Many people around the world live with depression, which can have a severe impact on their quality of life. While approaches like therapy and medication can help some people manage their symptoms, for others they are not that successful. Could diet succeed where other approaches fail, and if so, why?
Depression is such a common mental health disorder that it affects around 5% of all adults around the world, according to World Health Organization (WHO) estimates.
There are different types of depression — such as major depressive disorder and persistent depressive disorder lasting for at least 2 years.
The causes of depression are often manifold, with both genetic and situational risk factors involved — specific stressors or conditions, acting as triggers, leading to recurrent major depressive episodes.
And while targeted therapy and medication help many overcome or manage their symptoms of depression, these interventions do not work equally for everyone.
This has led researchers to cast their nets even wider in looking for all the factors that may contribute to depression, as well as for novel approaches for depression treatments and symptom management.
Recently, diet has come to the forefront of medical research, with experts debating the pros and cons of using dietary interventions to treat or even prevent different medical conditions.
Over the past few years, several studies have suggested that opting for healthier diets rich in vegetables, fruit, and whole grains may help improve depression symptoms.
For instance, one study from April 2022 from the University of Technology Sydney found that men aged 18–25 years experienced an improvement in depression symptoms after switching to a Mediterranean diet. But it remains unclear what mediates the link between diet quality and mental health.
In December 2022, two studies published in Nature Communications looked at the link between gut microbiota and depression symptoms. One of the studies found that 13 types of bacteria, in particular, are associated with depression symptoms.
It may be the way in which these bacteria lead to the activation of different signals in the brain that may explain the link between the bacterial makeup of the gut and depression symptoms, researchers hypothesize.
And this is also where diet comes in: By making certain dietary changes, we may be able to influence the abundance of certain bacterial species in the gut and, by extension, the communication between the gut and the brain, leading to an improvement in depression symptoms.
In this month’s installment of our In Conversation podcast, we discuss the whys and hows of diet’s potential impact on mental health, specifically on depression symptoms, with one of the authors of the Nature Communications study looking at gut bacteria and depression symptoms, Dr. Najaf Amin.
Dr. Amin is a senior research associate in the Nuffield Department of Population Health at the University of Oxford in the United Kingdom, and one of her areas of interest is using genomics data to zero in on biomarkers of neuropsychiatric traits.
Our other guest on this month’s episode is Rachel Kelly, a U.K.-based mental health advocate, writer, and journalist who has been outspoken about the ways in which dietary interventions helped treat her own instances of depression.
Kelly’s book, The Happy Kitchen, sold as The Happiness Diet in the United States, is a compilation of healthy recipes based on information gathered from nutritional studies whose aim is to boost mood and increase energy levels.
You can listen to this month’s installment of our podcast below, or on your preferred streaming platform.
Depression and the gut
In their study from 2022, Dr. Amin and her colleagues analyzed data from 1,133 participants in the Rotterdam Study, asking whether there was a link between the composition of the gut microbiota and experiencing symptoms of depression.
The researchers found that the presence of certain microbial genera — including Eggerthella, Coprococcus, Sellimonas, Lachnoclostridium, and Hungatella — were linked to depression.
“We identified 13 microbiota, and those were associated with depression. I think most of them were protective, so they were decreased in depression. And then there were a few [bacteria] that were increased in depression,” Dr. Amin explained in the podcast.
The abundance of some bacteria, in particular, such as those belonging to the Eggerthella genus, appeared to be connected to an increase in depression symptoms.
In their study, the researchers explain that these bacteria are involved in the synthesis of certain neurotransmitters, or chemical messengers, whose activity may, in turn, be involved in the expression of depression symptoms. These chemicals are glutamate, butyrate, serotonin, and gamma amino butyric acid (GABA).
Previous research has suggested that people with a diagnosis of depression have higher levels of glutamate in their systems than their depression-free peers, while lower-than-usual levels of butyrate have been linked to symptoms of depression in people with Parkinson’s disease. Lower levels of GABA are also tied to depression.
And while last summer, a major review of the literature cast doubts over the prevailing theory that low serotonin levels are at least partly to blame for depression symptoms, newer small-scale studies continue to contend that the serotonin theory of depression still holds ground.
Dr. Amin and her colleagues suggest that butyrate, in particular, may be of importance in explaining the potential mechanisms through which some gut bacteria might influence mental health.
“In the gut microbiome, you have the short-chain fatty acid-producing bacteria [which synthesize] the three short-chain fatty acids, including acetate, propionate, and butyrate. And all three of them, they act as energy providers also,” Dr. Amin explained in the podcast.
“But they also have the ability to change the expression of a gene, [to] switch it on [or] switch it off. It doesn’t change the genetic code, but what it does is it changes the levels of proteins that a certain gene is producing, so indirectly affecting what your genes are giving you,” she noted.
Why might diet be key?
From making the connection between the abundance of certain gut bacteria and symptoms of mood disorders, to arguing that diet may also play a role in “feeding” or reducing the expression and severity of depression symptoms, there is just one short step, Dr. Amin pointed out.
Many substances, including glutamate and butyrate, are synthesized by gut bacteria from a person’s diet, meaning that what a person eats will necessarily influence the abundance of those substances in the human body.
“The most important part [with] butyrate is that it is responsible for maintaining the intestinal epithelial integrity,” Dr. Amin explained. “So if you eat lots of fibers, whole grains, fruits, your gut microbiota [are] really happy, especially the short-chain fatty acid-producing bacteria — they’re very happy, they produce more short chain fatty acids, and the butyrate, it helps maintain this intestinal epithelial integrity.”
“So if you’re not taking, let’s say, enough fruits in your diet, what happens is that the number of short-chain fatty acid-producing bacteria that go down, your intestinal epithelial integrity is compromised. And what happens is, then you have the leaky gut syndrome, where the bacteria from your gut, they start migrating into the body and that creates an inflammatory response from the body, and oxidative stress. So this is why butyrate is so important — the short-chain fatty acids […] actually they are influenced by your diet intake.”
– Dr. Najaf Amin
But diet also influences the abundance of certain bacterial species in the gut, and since some bacteria synthesize certain substances, having too many or too few of some bacterial species can also lead to having too much or too little of some substances in our bodies.
This is a phenomenon known as dysbiosis, which can produce undesired effects both for physical and mental health.
“Studies have shown that […] you change your gut microbiome if you start taking a healthy diet, or when there’s a healthy diet [being followed already] — [for example, the] Mediterranean diet. There are lots of studies showing already that taking [a] Mediterranean diet over a long period of time does change your gut microbiome,” Dr. Amin told us.
The importance of diversity in diet
Our other guest, Rachel Kelly, shared that improving the diversity of foods in her day-to-day diet was, she felt, crucial to helping her overcome her symptoms of depression.
“I think that one of the huge changes, the biggest single change [I made to my diet] was adding a lot more variety,” she told us in the podcast.
Kelly said she started keeping a food diary to help her track what she was eating, and what she found gave her pause: “I found it rather painful, actually, because it’s […] pretty boring writing down everything you eat. But it’s quite striking what comes up, and it was just the repetition.”
“You know, I’ve got a family, and [when it came to meals] it tended to be roast chicken on Sunday lunch, and then it was fish pie on Friday, and my supermarket order was on repeat,” she said. “So one of the biggest changes was really adding lots of variety.”
Dr. Amin explained just how nutritional variety can help by acting on the gut:
“I think when you’re consistently taking […] [just] one type of diet, you might be reducing some of the chemicals that are being produced in the body and increasing some of the [other] chemicals. So the diversity in your diet is taking care of the fact that you are not overproducing a certain chemical, for instance, in the body. But if I go to a specific diet, we know now through the research, that there are some compounds present in these fruits and vegetables that are very, very healthy — antioxidants, for instance — that you get while you eat food.”
In short, a balanced, varied diet can help maintain bacterial balance in the gut and thus prevent or redress dysbiosis and the health problems it creates.
How does inflammation factor in?
One phenomenon that might mediate the impact of diet and gut bacteria on mental health might be inflammation. Inflammation can contribute to many health problems, including cardiovascular diseases, a decrease in cognitive performance, and even cancer.
Recently, some research has also suggested that inflammation could impact the availability of neurotransmitters such as dopamine, thereby contributing to some symptoms of depression, such as a lack of motivation.
“We already know that about 33% of the cases [of depression] are somehow related to inflammation,” Dr. Amin said in the podcast. “But the thing [is] that most of these cases of inflammation are actually having a comorbid condition like for instance, diabetes or hypertension, or any other disease that is causing the inflammation, and then [people] develop depression.”
“But in my own studies — two papers are coming out very soon — [I and my colleagues] have analyzed hundreds of chemicals floating in the blood. And what we found is [that it is] the energy metabolism, the oxidative stress that is disrupted.”
In cells, she explained, tiny structures, or organelles, called mitochondria are responsible for producing energy. When cells undergo oxidative stress — which can be caused by a number of factors, including disease and inflammation — the mitochondria are also affected.
And inflammation, she noted, can be caused by a poor diet, leaky gut syndrome, or even chronic exposure to everyday stressors.
“What happens is that when you are not having enough energy and also, let’s say, your gut microbiota is disturbed, or there is leaky gut syndrome, and then there is inflammation in the body — mitochondria are the first organelles to get affected by that oxidative stress. And when mitochondria start breaking down, or when they are affected, not enough energy is being produced. And that’s what I think is happening — […] your body first is going to inflammation, the inflammation is killing your mitochondria and then you are not able to produce enough energy.”
– Dr. Najaf Amin
“And one of the key symptoms of depression is that you don’t have energy,” Dr. Amin pointed out.
How to improve diet to fight depression
Both Kelly and Dr. Amin believe that, by taking positive control of one’s diet, people can take a step forward in fighting the symptoms of depression — or perhaps even in preventing it altogether.
While they both acknowledge that depression is a complex condition that can have multiple causes, they argue that dietary interventions can be an easy, self-empowering way of working towards better mental health.
And, importantly, a healthy diet does not come with a list of potential side effects, as does some of the most common antidepressant medication, such as selective serotonin reuptake inhibitors (SSRIs).
A therapeutic approach to depression that comes free of life-disrupting side effects — “this is what we are working towards, you know,” said Dr. Amin.
So what, then, might be some easy dietary changes that could reduce the impact of depression? Speaking from her own life experience and based on the nutrition research she has read, Kelly suggested taking small steps — and not removing our sources of so-called guilty gastronomic enjoyment altogether.
For instance, she suggested that dark chocolate can be a healthier and more beneficial alternative to milk chocolate, as it contains larger amounts of key minerals, such as iron, magnesium, and zinc, as well as antioxidants.
Research has suggested that magnesium supplementation can sometimes help improve symptoms of depression, and the antioxidants could help fight the oxidative stress that Dr. Amin believes could play a role in depression.
Kelly shared some other easy dietary recommendations with us:
At the same time, she emphasized, diet should only be one of several approaches when it comes to fighting depression symptoms. There are many other things that people can do in a bid to feel more themselves, she pointed out.
“We talked a bit about stress, and stress has an impact in terms of our microbiome, how well we’re digesting. So you’ve got to put in some other stress reduction methods as well, whether that’s your therapy, meditation, your mindfulness, your exercise — that’s going to make the nutritional changes much more effective.”
– Rachel Kelly
Dr. Amin also acknowledged that opting for a healthier diet does not have to be an act of self-sacrifice. “If you want to indulge in your piece of donut go ahead, eat it,” she said.
“But do compensate it with fruits, healthy foods, [a] healthy diet, vegetables, green leafy vegetables, and whole grains (wholemeal). And yeah, just balance it [out].”
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