Researchers looked at seven studies that involved probiotic and prebiotic therapy in depression and anxiety disorders. They found significant improvements in one or more outcomes related to their symptoms, even among those with more severe depression. However, some of the studies indicated this needs to be maintained for the benefits to keep going. For example, one study cited by the review showed improvements after eight weeks of daily probiotic use, but those gains were undone after eight more weeks without probiotics.
The Gut-Brain Axis
The importance of the gut in emotional and cognitive function is so strong that it’s often called “the second brain.“ Think of the gut-brain axis as a bidirectional superhighway with plenty of speeding traffic, representing the chemical signals sent between the brain and the digestive system. These signals are incredibly important for your autonomic nervous system, endocrine system, and immune system. Although your brain sends messages down to your digestive system—if you get butterflies in your stomach before a presentation, for example, or feel nauseated during times of high stress, that’s your gut-brain axis at work—that highway definitely runs in the other direction as well. A big example is serotonin, a neurotransmitter that has a range of functions in the body, and is so integral to mood and overall wellbeing that it’s called “the happy chemical.” Although it plays a major role in brain function, it’s estimated that 95% of your serotonin is made in the digestive tract. Some standard therapies actually rely on this connection as well. For example, a common medication type for mood disorders, anxiety, and depression is a selective serotonin reuptake inhibitor or SSRI. This works by increasing levels of serotonin in the brain by blocking the reuptake process, so serotonin doesn’t reabsorb into the system as quickly. That serotonin is coming up through the gut superhighway to the brain.
Getting the Good Bacteria
Whether you’re feeling emotionally challenged or not, increasing gut-friendly foods can be a boon for health, including blood sugar regulation and lowered inflammation, according to registered dietitian Michelle Routhenstein, RD, owner of nutritional counseling practice Entirely Nourished. Fermented foods are particularly good for this, including:
YogurtKefirKimchiSauerkrautBeet kvassKombuchaFermented Pickles
Those tend to increase the diversity of your gut bacteria, and keeping them thriving once they’re in the gut is the work of prebiotics, which includes foods rich in dietary fiber such as:
OnionsGarlicWhole grainsBananasBeans
For a bigger serotonin boost, Routhenstein recommends folate-rich foods, which can cause the hormone to release into the brain more efficiently, she says. These include dark, leafy green vegetables like spinach and collard greens, as well as asparagus, broccoli, chickpeas, and lentils. Although there are supplements—and plenty of them—that offer probiotics and prebiotics, Routhenstein and other dietitians suggest trying to get as much as possible from foods before going that route. That’s because you’ll also be getting other nutritional benefits of these healthy choices like vitamins, minerals, and fiber that also support better gut health. Furthermore, while alternative therapies like probiotics and prebiotics are promising, there’s not enough evidence yet to warrant using them in place of medication you may be taking rather than in conjunction with your meds. Experts caution that abruptly stopping meds used for mental health concerns can be dangerous, and shouldn’t be done on your own without medical guidance.
