Sour cabbage – Professor of Probiotics The first and most overlooked reason that our digestive tract is crucial to our health is because 80 percent of our entire immune system is located in your digestive tract. In addition, our digestive system is the second largest part of our neurological system, called enteric nervous system or the second brain. Probiotics are live beneficial bacteria, which hold the master key for healing digestive issues, better health, stronger immune system, mental and neurological disorders. Sour cabbage is the best probiotic food (Germans call it Sauerkraut), It is produced by lacto-fermentation of the cabbage.