Fermented foods (and beverages) have been a part of cultures around the world for thousands of years, as fermentation provides a way to preserve foods, gives them additional nutritional value and/or medicinal properties, and adds flavor. In addition to those benefits, researchers are discovering that consuming fermented foods can contribute to positive mental health, as the beneficial bacteria in these products have a positive effect on our microbiome.1
What is the microbiome?
The microbiome is the community of microorganisms that live in our body. One of the most important parts of the microbiome is the intestinal microbiota, which encompasses the helpful bacteria in our intestines (previously called the gut flora). The intestinal microbiota has many functions, including:
Helping maintain the integrity of the intestinal wall 2
It’s estimated that approximately one-third of gut microbiota are common among people, but two-thirds are unique to the individual. Generally, the more diverse the microbiome is within an individual, the healthier they are.2
How does diet impact mental health?
Rates of depression have increased as societies have moved away from traditional lifestyles, and diet is one area that researchers are finding plays a significant role. The brain, like all the body’s organs and tissues, relies on the nutrients from the diet for its health and functioning, and the medical community is starting to recognize the importance of diet in mental health. In recent years, a new field has been gaining momentum – nutritional psychiatry – with many studies finding a connection between nutrition and mental health.1
Traditional dietary practices (like the Mediterranean or Japanese diet) typically have more fruits, vegetables, fish & seafood, and fiber, and low amounts of dairy and lean meats, compared to the Western diet, which contains more processed and refined foods, and a higher intake of sugar and fat. Many studies have found a link between traditional dietary practices and lower rates of depression and anxiety. Some studies have found that closely following a traditional healthy diet can reduce your risk of depression by 25%-30.1,3,4
Some specific food items in traditional diets that have been identified as having a protective effect against depression include soy foods, turmeric, cocoa, green tea, coffee, pomegranate, blueberries, and honey. These foods and the isolated compounds within them are also being studied for their antidepressant properties. Nutrients such as magnesium, zinc, vitamin C, folic acid, and vitamin B12 have also been connected to a resiliency against depression as well as improving depressive symptoms.1
Inflammation and mood
One area of continued research is the interplay between chronic inflammation, mental illnesses like depression, and the gut. Some research has discovered that the intestinal barrier might be compromised in depression. Other known factors that can negatively affect the intestinal barrier are psychological stress, exhaustive exercise, and a Westernized diet high in fat and sugar.1
When the permeability of the intestinal barrier is increased, more environmental toxins and food antigens (which can cause food intolerances or allergies) are introduced into the body. A damaged intestinal barrier is also associated with higher levels of a chemical known as lipopolysaccharide endotoxin (LPS). When LPS levels increase, depression increases, inflammation in the body increases, and blood sugar control is impacted. Traditional diets lower LPS, while the Western diet increases LPS.1
The microbiota and mental health
Researchers have found that the variety and health of the intestinal microbiota has many effects on mental health, including:
Influencing the production of neurotransmitters (chemical messengers that interact between neurons; imbalances of the neurotransmitters serotonin, norepinephrine, and dopamine have been linked to depression) 5
Activating the neural pathways between the gut and brain
Limiting inflammatory processes
Improving nutritional status
Limiting intestinal pathogens and bacterial overgrowth
Providing analgesic (pain-relieving) properties
Reducing the toxin burden 1
While experts believe that it’s best to obtain beneficial nutrients through the foods you eat, several studies comparing oral probiotic supplements to placebo have found that adding probiotics may decrease anxiety, reduce symptoms of depression, diminish perceptions of stress, and improve mental outlook. Though many of the mood changes are self-reported, a placebo-controlled study that used magnetic resonance imaging (MRI) showed that people receiving a fermented food with probiotics had increased brain activity. This study has been well-received, although the increased brain activity could be due to the ability of fermented food influencing the central nervous system. Additional studies are needed to understand if the increased brain activity is due to a probiotic alone or the probiotic within fermented food.1
The potential of fermented foods
Fermented foods made through a traditional fermentation process have been shown to produce novel compounds that provide immune, glycemic (blood sugar), and anti-inflammatory properties. Fermented foods are also more likely than a probiotic supplement to contain a variety of good bacteria, and the synergy between the different bacteria types seems to provide more benefit to the body than they would on their own.1
Many dietary items go through a fermentation process, but not all fermented foods provide the same benefits. Fermented foods that have been studied in research and found to provide health benefits include:
Fermented dairy products, like yogurt and kefir
Fermented soy, soy germ, soy milk and soy sauce
Fermented rice bran and wheat bran
Sourdough bread and other breads made via fermentation techniques
Fermented mung beans, buckwheat sprouts, and lentils 1
What does this mean for me?
The evidence from research is compelling that fermented foods, as well as a more traditional way of eating, have profound benefits for our overall health and mood. In addition, the research is suggesting that the consumption of convenient, high-fat or high-sugar foods are not only bad for optimal nutritional status, they are damaging our microbiome and our brain’s ability to function. As every individual is unique, talk to your doctor or a nutritionist if you’re considering adding probiotic supplements or more fermented foods to your diet.1
Selhub EM, Logan AC, Bested AC. Fermented foods, microbiota, and mental health: ancient practice meets nutritional psychiatry. Journal of Physiological Anthropology. 2014;33(1):2. doi:10.1186/1880-6805-33-2.
Jandhyala SM, Talukdar R, Subramanyam C, Vuyyuru H, Sasikala M, Nageshwar Reddy D. Role of the normal gut microbiota. World J Gastroenterol. 2015 Aug 7;21(29):8787-803. doi: 10.3748/wjg.v21.i29.8787.
Jacka FN, Pasco JA, Mykletun A, Williams LJ, Hodge AM, O’Reilly SL, Nicholson GC, Kotowicz MA, Berk M. Association of Western and traditional diets with depression and anxiety in women. Am J Psychiatry. 2010;167:305–311. doi: 10.1176/appi.ajp.2009.09060881.
Sánchez-Villegas A, Delgado-Rodríguez M, Alonso A, Schlatter J, Lahortiga F, Serra Majem L, Martínez-González MA. Association of the Mediterranean dietary pattern with the incidence of depression: the Seguimiento Universidad de Navarra/University of Navarra follow-up (SUN) cohort. Arch Gen Psychiatry. 2009;66:1090–1098. doi: 10.1001/archgenpsychiatry.2009.129.
Havard Medical School. Accessed online on 9/13/17 at https://www.health.harvard.edu/mind-and-mood/what-causes-depression.