Until the advent of refrigeration units, our ancestors relied on many forms, of food preservation. One of these methods was fermentation. In this process foods is kept in an acidic solution that slows the rate of deterioration and makes it so the bacteria produced is healthy for human consumption. This process can create microbiotic compounds that help boost the bodies functions and immune system.
While we have known that fermented foods boosts the digestive system, we didn't realize the benefits it could have on mental health. A study conducted by the College of William and Mary, had 700 participants eat higher levels of fermented foods for thirty days. These foods included yogurt, kefir, fermented soy milk, miso soup, sauerkraut, some dark chocolates, microalgae juices, pickles, tempeh and kimchi.
The participants should less anxiety and depression after consuming these foods. While it is difficult to prescribe a blanket amount of consumption for everyone, as digestive ecosystems vary greatly from person to person, there doesn't seem to be a tipping point.
Eating these foods in excess doesn't seem to have a down side. It can only seem to help. So give it a try, starting with one fermented food a day and build from there!