(To get some background on this topic, you may want to start here with my post discussing the gut-brain axis in more detail.)
Assuming we're all on the same page that the health of our "second brain" is vital to our mental health, let's jump right into some of the factors that influence the gut-microbiota-brain axis, and the places where we can have an impact through nutrition and lifestyle.
The Microbiome, Probiotics and Prebiotics
One of the most dramatic changes in the perspective of medical science in the past 20 years has been the shift in the way we view bacteria. We’ve shifted from the hygiene model (where the more sterile we could make our environment, the better) to understanding that we not only have massive numbers of microbes (bacteria, fungi, and viruses, etc.) inside and outside of our bodies at all times, but that we actually need and benefit from them.
Unfortunately, the traditional Western-style diet is pretty deficient in the favorite foods of those healthy gut bacteria: fibers (also called prebiotics).
While there are lots of things that influence our gut microbiome that we don't have much control over, there are also some pretty substantial things that we do have control over, and research has shown that the impact of some dietary changes can be seen as soon as 2-4 days - though it takes much longer to have a substantial and lasting impact.
The foods we eat and the types of fibers that they contain can have a direct impact on which kinds of microbes flourish in our intestines, and which types don't. Eating foods that contain healthy bacteria (also called probiotic foods – things like yogurt with live and active cultures, sauerkraut, and miso) can also have a positive impact.
And in turn, promoting the growth and flourishing of these healthy bacteria has been shown to increase their production of the neuroprotective short-chain fatty acid butyrate, improve our stress response, optimize immune function, impact neurotransmitter function in the brain, decrease symptoms of depression, alleviate anxiety in children with autism spectrum disorder, and more.
The importance of nutrition - adequacy of energy (calories), vitamins, minerals, amino acids, fiber, essential fats, and carbohydrates - really can't be understated when it comes to mental health.
When it comes to good nutrition, calories are just the beginning. Even the macronutrients (carbohydrates, protein, and fat), while very important, are just the beginning. Most of us get enough of these things in general (though we’ll talk more about the specifics of types of protein and types of fat in a minute).
But what about vitamins and minerals? Many of us tend to eat diets that are full of a lot of processed foods which are energy-dense (plenty of calories) but nutrient-poor (depleted of a lot of the vitamins and minerals that whole foods, like produce, meats, fish, beans, nuts and seeds, etc. contain). We often don’t eat enough fruits and vegetables - and especially vegetables.
Eating diet rich in whole plant foods (and maybe even growing our own when we can, for optimal nutrient quality and a healthy connection to nature) goes a long way towards getting us the essential vitamins and minerals that we need, as well as the fiber to feed that lovely gut microbiome.
But for some people, it seems that even a nutrient-dense diet doesn't go far enough to meet their nutrient needs. For a variety of reasons, some people have higher needs for certain vitamins and minerals than we might think based on the estimates of the RDAs (i.e., the percentages listed on the nutrition label).
A growing body of research is showing that increased needs for certain vitamins and minerals, especially things like B vitamins, vitamin D, magnesium, and zinc, might be linked to certain mental health conditions.
Amino acids are the building blocks of protein molecules, and there are 9 that are considered essential – meaning that we have to eat them in our diets because our bodies can’t make them.
Amino acids are also the precursors for neurotransmitters in the brain. Seven of the essential amino acids are also essential for making neurotransmitters: valine, leucine, isoleucine, lysine, phenylalanine, histidine, and tryptophan. Diets that are deficient in these amino acids can cause deficiency of neurotransmitters – things like GABA, serotonin, and dopamine – and can cause mental illness-like behavior.
It’s worth noting that amino acids are also the major fuel of the cells of the intestines, so deficiency in amino acids not only affects the brain and neurotransmitter levels directly, but also via the gut-brain axis, as poorly-nourished intestinal cells aren’t able to continually replicate and renew the gut lining the way that they need to.
Omega-3 Fatty Acids
One widely-studied nutrient group is the polyunsaturated fatty acids, including omega-3 and omega-6 fatty acids. While some amounts of each are essential for our health, omega-3 fatty acids are known to decrease inflammation, and they also seem to play a role in promoting a healthy gut microbiome.
Most of us eat far more omega-6 than omega-3 fats. Eating more nuts (especially walnuts), seeds (especially flax seed), and low-mercury fatty fish (like anchovies, salmon, or halibut) can help us improve our omega-3 fatty acid intake.
While supplementing with omega-3 fatty acids (like DHA and EPA) has produced mixed results in clinical trials, we do see a clear benefit to mental health from eating foods that contain omega-3s.
In the case of supplements, there does seem to be a benefit to supplements with the right ratio of EPA to DHA for some people with major depressive disorder, schizophrenia, and bipolar disorder, but it’s always a good idea to consult with a doctor, psychiatrist, or dietitian with expertise in nutritional psychiatry to help decide whether a supplement is right for you, what dosage, and what ratio of EPA to DHA, as this varies depending on the person and depending on the diagnosis.
Polyphenols are anti-inflammatory compounds found in plant foods such as grapes, pears, berries, cherries, tea, cocoa, legumes, grains, coffee, and apples. Resveratrol and curcumin are two well-known examples of polyphenols.
The majority of these compounds are actually fermented by the gut microbiota first to allow our bodies to absorb and use them, and they play a role in preventing dysbiosis - promoting a healthy balance of bacteria in our intestines.
Polyphenols have been shown to reduce inflammation, protect the brain from cellular damage, play important roles in learning and memory, and balance neurotransmitter levels in the brain.
Inflammation and mental illness are inextricably linked. While we used to think that inflammation in the rest of the body had no impact on the brain, shielded as it is by the blood-brain barrier, we now know that systemic inflammation (both acute and chronic) has a significant impact on the functioning of the brain. So, managing inflammation with tools like the Mediterranean or other anti-inflammatory eating patterns is important in managing mental illness.
Several wonderful studies have been done on variations of the Mediterranean diet in improving mental health and reducing symptoms of depression. It’s worth noting that polyphenol-rich olive oil is a key component of the Mediterranean diet, which may be part of why it’s so effective in improving mental health, along with the emphasis on nutrient-dense foods, omega-3-rich fish, nuts and seeds, and plant fibers.
Food Allergies and Sensitivities
For some, food allergies and sensitivities can be significant causes of inflammation, both in the gut and in the body as a whole.
When we eat foods to which we are allergic, our bodies respond as if we’re at war, with a massive inflammatory cascade that seeks to destroy the enemy invader - and ends up damaging our own body tissue and possibly even threatening our lives.
While less severe, food sensitivities have been found to have some negative long-term health impacts on people who eat significant amounts of these foods to which they are sensitive. The gut can become inflamed and irritated, which can cause some obvious side effects like diarrhea or abdominal pain for some, in addition to causing the tight junctions between the intestinal cells to open up and allow molecules that are a bit too big to come through. (This is called intestinal permeability, though it’s been nicknamed “leaky gut.”)
This can contribute to inflammation throughout our bodies and brains, change the composition of our gut microbiome, and possibly even contribute to a “leaky” blood-brain barrier.
Rates of food allergies and sensitivities are known to be increased in children with ADHD and individuals with schizophrenia, for example, and there are also high rates of depression and anxiety in people with severe food allergies – though the cause or connection is still unclear.
Though it doesn't totally fall under the umbrella of the gut-brain axis, exercise is worth mentioning anytime we talk about mental health and lifestyle change. Exercise has been dubbed by some the "best anti-depressant." It doesn't require skill, money, or even much of a time commitment. Anyone can do it from anywhere, and it's incredibly effective in improving mood, reducing symptoms of depression and anxiety, improving sleep (which itself is important in stabilizing mood), and more.
Along with its many, many other health benefits, exercise also influences the gut microbiome. Exercise can increase the numbers of "good" bacteria, as well as boost the diversity of microbes in your gut.
While there are lots of dietary and lifestyle factors that we already know influence our gut microbiome, it’s a relatively new field, and we're probably only just scratching the surface so far!
But if you want to make some concrete changes to improve your gut health and mental health, here are some ideas for where to start.
If you have any questions, feel free to comment below or message me directly. If you’d like more personalized guidance, schedule an appointment with me! I’d love to work with you.