Trust your gut, they say. While it is cliche, there might be something too this saying. Maybe it should be trust your gut microbiota, but only if it's healthy. As you know, the human body is a complex collection of different intricate parts that all have to be communicating and working in sync to have you feeling your best. That's a lot of work for just one you! Lucky now we know that we don’t have to do it alone. We are working with the help of up to 100 trillion microorganisms. Most of these live in our guts. This is where the term ‘gut brain connection’ comes from. We are beginning to better understand the interplay between the gut microbiota and not only digestive, but mental health as well. This is mainly through the regulation of inflammation and signaling molecules, which will be discussed in further detail below.
Our gut microbiota are unique to us as individuals, and what may be ideal for one person may not be the same for another, but there are hallmarks of a healthy gut. These include the presence of certain common species bacteria, large bacterial diversity, and abundance of bacteria. While it might seem like the bacteria are localized to the gut, just like everything else in our bodies, everything is connected. The most talked about way these bacteria interact with other parts of our body is through the guts interaction with the hypothalamic-adrenal-pituitary axis, commonly called the gut-brain connection. For those of you unfamiliar, the hypothalamus, adrenals, and pituitary glands are part of the endocrine system, or system responsible for hormones in the body. If there is a poor gut-brain connection, the bacteria interacting with the brain and endocrine system can cause an inflammatory cascade. This in turn increases sympathetic reactivity. It is important to note that physiological and psychological stressors as well as genetic vulnerability play a large role in the presence of almost all neurological conditions (including mental health conditions) and have some correlation to inflammation.
How can bacteria cause this shift in systemic inflammation? Having an unhealthy gut microbiota means that there is less of a barrier in your intestine. This can cause more inflammatory molecules to leak through and enter your systemic circulation. Sometimes some molecules will even cross the blood brain barrier. Bacteria can interact more directly with the brain by releasing neurotransmitters in the gut, which bind to vagus nerve receptors there. A healthy gut microbiome might even have a calming effect on the amygdala, which has receptors for gut peptides, a concept that will be defined when discussing the effect of diet on the microbiota. Having bad bacteria can cause the opposite effect and release chemicals that induce stress and anxiety when they pass through the compromised intestinal wall.
The gut microbiota plays such a large role in mental health conditions that researchers have been able to determine if a patient has depression with 97-100% accuracy just by looking at their gut microbiota. They have also identified patterns of altered gut microbiota with alzheimers, schizophrenia, and anorexia. In these people, the introduction of positive bacteria species has been shown to negate those negative effects and help lower inflammation and signaling molecules. A decrease in anxiety and depression was also observed. Similarly, compared to people receiving a placebo, people receiving probiotics reported better mood and showed blood oxygen signal patterns related to better emotional decision making and emotional recognition when tested. Probiotics both alone and paired with antidepressants have been shown to improve depressive symptoms, and decreased reactivity to poor mood compared to those not taking probiotics. One study investigated the effect of giving infants probiotics consisting of bacterial strains present in our evolutionary history but now uncommon due to water and soil treatment and found that when supplemented there was a significant decrease in ADHD and autism spectrum disorders.
So, are you destined to live with the microbiome you already have? No! Many things can affect your microbiota. Stress, poor diet, poor sleep, negative emotional states, and baseline health conditions can all affect the bacteria in your gut. Bad bacteria can increase your risk for anxiety, high stress can also harm the healthy bacteria in your gut and cause the bad ones to increase in prevalence in a sort of vicious circle. Poor sleep can have a similar effect. However, there are things you can do to promote a healthy gut.
Trying to regulate stress and sleep is a good starting point but diet is also a very potent part of the equation. A diet stressing whole foods, particularly one high in fiber, with sufficient vitamins and minerals and fatty acids in sufficient quantities for optimal brain function promotes not only your health but that of your microbiome as well. One study showed an inverse relationship between fruit and dairy and depression scores, all the more reason to go out and get that charcuterie board. Including omega-3 fatty acids into the diet is also health promoting, as they are anti-inflammatory and act as signaling molecules which promote healthy gut microbiota and neurotransmitter activity. At least 2 grams of omega-3s with more DHA than EPA is effective in reducing depression symptoms.
Avoiding some things common in the standard American diet, particularly refined sugars and processed vegetable oils is also important. Unfortunately for those who are fans of diet or sugar free versions of foods, artificial sweeteners should also be avoided as they have been shown to alter hormone levels in the amygdala, increase overall inflammation, and impact systemic metabolism. If you are not willing to give up sweeteners, stevia and erythritol are the best options. Alternatively, whole foods like dates and honey are better, if you are willing to put in the extra effort to incorporate these into your drinks/foods.
While in a healthy population, following a gluten free diet is linked to increased depressive scores, in some populations it may be highly beneficial. What does gluten have to do with this? While it used to only be those with celiac disease that were aware of gluten, today we see gluten free diets, special foods and claims about how gluten affects the body throughout the media. But what is gluten? It is a protein found in many grains, and therefore grain products like breads, flours, cereals, ect. For those with celiac disease or gluten sensitivity symptoms of ingesting gluten can range from a slight inconvenience like an upset stomach to something as serious as death. The common symptoms include upset stomach, bloating, poor digestion, nutrient deficiencies.
While to those without gluten sensitivity or celiac disease the research has found no downside to it, in those with these conditions ingesting gluten can be very harmful to not only the GI tract but also the central nervous system, including the spinal cord and brain. This is due to its impact on the intestines and the bacteria living there. In those with celiac, ingesting gluten causes damage to the intestinal wall, resulting in a condition called leaky gut. This increases the likelihood of the passage of harmful chemicals to the blood. In those with gluten sensitivity, there is no physical damage to the intestinal wall but there are increased antibodies (an inflammatory response that also inflames the brain). In both groups, avoiding gluten reduces inflammation. Due to the strong correlation between inflammation and neurological conditions, this diet can improve mood disorders and other neurological conditions.
For people with symptomatic versions of celiac and gluten sensitivity, following a gluten free diet has been shown to significantly improve mood. Avoiding gluten can also reduce some of the stress that comes with managing a chronic condition like celiac. Because of the cyclic nature of the relationship between mood and microbial health, the reduced stress can help promote a healthy gut microbiome and further improve mood. It is also important to note that there are many people out there who may not know they have gluten sensitivity. If you suspect that you might, it is worth going gluten free for a few months to see if avoiding gluten could potentially improve your mental and physical health.
Eating a healthy diet low in processed foods and high in whole grains, complex carbs, healthy fats like omega 3's and with a wide veriety is critial to both phyiscal and mental health. If you are having trouble figuring out how to do this, get help from a dietitican. If you think you are doing a good job but something still seems off, or you are just curious it can also be very worth while to do a food sensitivity test to test for things like gluten sensitivity. Knowing what foods trigger you can lead to a healthier gut, mind, and overall life.
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