That is the question I am asked the most often when discussing fermented foods. I always say at least five per week, though one or two a day is even better and there should be a variety. In other words you cannot just eat yogurt and think you have taken care of yourself. This just seems like common sense to me. Our ancestors, who maintained their gut health with fermented food, had several types in their diet. However, this has just been my best guess.
Finally, a study has come along to begin to answer this question. Published in the Journal of Dairy Research, the study looked at people who consumed at least 5 fermented dairy products such as yogurt and cheese and at least 3 other fermented products a week. The volunteers were asked to remove all fermented foods for two weeks. Blood and fecal samples were taken throughout the study. After two weeks without these foods, researchers found that gut bacteria levels had decreased and participants had a lower immune response – that is after just two weeks of no fermented foods.
Participants were then asked to consume either plain yogurt or yogurt, fortified with extra probiotic strains for another two weeks. This stopped the decline of the gut bacteria levels and the immune response but neither of the two yogurts could restore gut levels or immune response back to where they were prior to the removal of the fermented foods from the diet.
This has a lot of implications. First, there is a complex relationship between different strains of bacteria, making diversity and variety of strains an important consideration. Second, a lot of time and money is currently being spent studying specific strains in hopes of creating super probiotics to cure conditions. Some research even involves combining strains and patenting the combination. This study shows that the complexity of the situation may make it not that easy for researchers to circumvent nature, on their way to developing commercial products.
The good news is that for us, it is a lot easier. We just have to find a few types of fermented foods and eat them (or drink them) consistrntly. There are so many to choose from. From the aged cheeses, yogurts and kefir to kombucha, sauerkraut, kimichi, wine, unpasteurized beer, miso, apple cider vinegar. Go to ethic stores and talk to the owners to find new ones. Or make you own. Fermenting combinations of vegetables with spices and herbs allows you to create fermented foods you love. Then all you have to do is make sure you consume them on a regular basis. If you like them, then that should not be too hard, right?
- Dietary deprivation of fermented foods causes a fall in innate immune response. Lactic acid bacteria can counteract the immunological effect of this deprivation. Olivares M, Paz Díaz-Ropero M, Gómez N, Sierra S, Lara-Villoslada F, Martín R, Miguel Rodríguez J, Xaus J., J Dairy Res. 2006 Nov;73(4):492-8. Epub 2006 Sep 21.