Fermenting foods is an ancient art. It’s one of the oldest types of food processing, second only to cooking.
Recently, fermented foods have experienced a resurgence in popularity.
Certain fermented foods, such as live yogurt and some cheeses, have been popular in the West for a long time.
Others that were virtually unknown in the West a few decades ago are now widely familiar, like kimchi, kombucha, kefir, tempeh, and miso.
Of course, just because something’s ancient (or popular) doesn’t make it healthy. However, evidence is mounting that fermented foods might benefit gut health.
In fact, Prof. Tim Spector, ZOE’s scientific co-founder, lists eating fermented foods in his top five tips for a healthier gut microbiome.
Beyond the gut, some scientists are investigating whether fermented foods might help improve mental health.
In this feature, we’ll walk you through the latest science and ask how fermented foods might benefit your mental health.
Food and mental health
Currently, the most common treatments for mental health conditions, such as depression and anxiety, are medicines and talking therapies. Some people do benefit from these, but they don’t work for everyone.
Experts are keen to find other ways to address these common conditions.
Over the years, an increasingly convincing body of evidence has built up to support links between food and mental health.
For instance, studies have shown that closely following the Mediterranean diet protects against depression.
Another study found that a high-quality diet based on the Mediterranean diet reduced symptoms of depression in people diagnosed with the condition.
However, scientists are still working to identify the roles of specific types of food on mental health.
Why fermented food?
Fermented foods contain live microorganisms, which may occur naturally or be added during manufacturing.
These foods have certain components that might benefit mental health, including:
Probiotics: the microorganisms themselves
Prebiotics: compounds that support the growth of microorganisms
Bioactive compounds: compounds, produced by microorganisms, that can interact with your body
Individually or combined, these components may have a range of effects, including:
altering your gut microbiome and increasing diversity
supporting immune function and decreasing inflammation
improving the digestibility of food
protecting against a "leaky" gut
That’s an impressive array of effects, but what does this mean for mental health? Why might these actions make a difference to mood? Let’s unpack them.
Some drivers of depression
Though depression affects around 5% of people globally, why it affects certain people and not others remains unclear. However, there are a few factors that might vary between individuals.
Running through the numbered list above, we’ll outline some of the elements that may be involved in depression and how fermented foods might help.
To be clear, there are a lot of hypotheticals and maybes in this article. Not all of these relationships have oodles of evidence to back them up, but they provide insight into how fermented foods could affect mental health.
1. The gut microbiome
The microorganisms in your gut interact with your gut, and your gut communicates with your brain. In reverse, your brain communicates with your gut, and those messages influence your gut bacteria.
Scientists call this two-way conversation the "microbiota-gut-brain axis."
Although much of the research so far is in animals, there’s growing evidence that your gut microbes play a part in mental health using these channels.
If fermented foods support a healthy gut microbiome, this could potentially benefit or protect your mental health.
2. Inflammation and the immune system
Inflammation is your immune system’s response to infection or injury. It’s a healthy response, but if it continues for long periods, it can damage your body.
For instance, researchers have found that people with depression have higher levels of certain compounds associated with increased inflammation.
Because some evidence shows that fermented foods might enhance the immune system and reduce inflammation, they might reduce mental health symptoms in this way, too.
3. Nutrients and depression
Some nutritional deficiencies may be linked to depression. For instance, there’s some evidence that a low intake of B vitamins might be related to the condition.
Interestingly, some gut bacteria can also synthesize vitamins, including vitamin K and B vitamins.
By supporting your gut microbiome with fermented foods, you may also reduce the risk of these deficiencies.
4. A ‘leaky’ gut
The lining of your gut makes sure that unwanted compounds don’t move from your gut into your blood.
In some people, this lining becomes “leaky.” When this happens, damaging compounds can enter the bloodstream. The immune system is alerted, and this sparks inflammation.
And, as we mentioned in the numbered list above, fermented foods might help protect against a “leaky” gut. However, scientists have only found evidence for this in animal models so far.
So, considering all of the above, it seems plausible that fermented foods could influence mental health. But is there any evidence that they do?
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Evidence so far
Currently, only a handful of studies have directly looked at the links between fermented foods and mental health in humans.
We’ll take you through some of these rare investigations.
Looking at a population
One of the very few large observational studies looking at mental health and fermented foods was published in 2015. It looked at social anxiety in a group of 710 young adults.
Participants filled out questionnaires to assess what foods they ate (including fermented foods), and their levels of social anxiety and neuroticism.
In this context, neuroticism describes a group of traits, including a disposition toward negative mood, anger, anxiety, self-consciousness, irritability, emotional instability, and depression.
The results suggest that people who scored high for neuroticism and consumed fermented foods had fewer symptoms of social anxiety. The authors write:
“Consumption of fermented foods that contain probiotics may serve as a low-risk intervention for reducing social anxiety,” particularly for those most at risk of social anxiety.
One study tested probiotic-containing fermented milk in a small group of women without gut or mental health issues.
The scientists gave 12 participants a fermented milk product twice daily for 4 weeks. They also had two control groups: 11 women drank non-fermented milk, and 13 received nothing.
At the start and end of the study, the researchers scanned the participants' brains — while the participants were at rest and while they were doing a task that involved looking at faces displaying emotions.
People in the fermented milk group showed changes in the activity of brain regions responsible for processing emotion, but the control participants didn’t.
Although this was a very small study, it hints that fermented foods might make changes in the brain relevant to mental health.
In another study, 93 women without depression took either red fermented ginseng capsules or a placebo for 2 weeks.
At the end of the study, those taking the fermented ginseng reported fewer depressive symptoms. Again, though, this is a relatively small study.
Another investigation looking at fermented red ginseng recruited 60 people with non-small cell lung cancer who were undergoing chemotherapy. For 60 days, 34 of them took ginseng with their chemotherapy, while the remainder just had chemotherapy.
Those taking the fermented ginseng reported less depression and anxiety than those who had chemotherapy alone.
However, it’s important to note that there was no control group taking non-fermented ginseng, so it's possible that other compounds in the ginseng caused this effect.
Other researchers have asked whether fermented foods might reduce feelings of stress. Two such studies focused on students embarking on exams — a time when stress levels are naturally high.
Both studies compared a fermented milk product with a non-fermented placebo milk.
In one study, the researchers measured levels of cortisol, a hormone that increases with stress. They found that only students in the placebo group experienced a rise in cortisol levels.
In the other study, the researchers found that students who consumed the fermented drink had fewer physical symptoms of stress than the control group.
Once again, these are small studies in specific groups of people, so it’s difficult to know whether the results would be relevant to society at large.
A fly in the fermented ointment?
Understanding how diet affects health is a complex topic. Understanding how and why mental health conditions arise is likewise complex.
So, when you add the two topics together, guess what? It’s complicated. And curve balls are frequent.
A recent study, which also focused on students with stress, is a good example. The researchers recruited 372 participants and took information about their fermented food consumption and any mental health conditions they had.
The researchers found that for students with mental health conditions, those who ate the most fermented food had fewer depressive symptoms than those with mental health conditions who ate little fermented food.
However — and here’s the added confusion — the students with no mental health conditions who ate the most fermented food had more symptoms of depression and anxiety than those eating little fermented food.
So, that’s the opposite of what we might have expected.
In agreement, another study on 372 “psychiatrically healthy” students found that those who ate the most fermented food were more likely to experience symptoms of depression and anxiety when stressed.
These results suggest that fermented foods might only benefit people with mental health conditions. However, diets are complex, and many other variables might come into play.
Importantly, these types of studies can only show associations.
For instance, the authors of the last study we mentioned suggest it’s possible that people with mental health conditions choose to eat more fermented foods, rather than fermented foods leading to an increase in symptoms.
A recent large-scale study looked at fermented food consumption among more than 26,000 people in Korea.
They compared those who ate the most fermented foods with those who ate the least. Men who ate the most had a lower likelihood of developing depression, but that effect didn’t show up for women.
As we said, it’s complicated. And that’s no surprise, really. There’s huge variation among people’s diets, the type of fermented food they eat, how each fermented food is produced, and the strains of bacteria within it.
There’s also a wide range of causes of mental health conditions, and exactly why these conditions arise might differ from person to person. We should expect nuance.
So, should you eat kimchi or not?
Overall, evidence that fermented foods can improve mental health is fairly weak. However, that’s not because studies have failed to find an effect, it's because scientists haven’t done many studies yet.
And as we’ve mentioned, diets are complex, and various components within food might influence mental health symptoms. Separating out their effects is very challenging.
Perhaps, as we keep investigating, we’ll find deeper links. But, to answer the question just above, if you like fermented foods, they do seem to benefit health generally.
So, adding them to your diet is likely to be good for your health — and who knows, it might also give you a mood boost at the same time.
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