Adapted from Digestion Connection by Elizabeth Lipski, PhD, CNN, CHN, Rodale, 2013. The digestive system is like a river that runs through us. Each day we put pounds of foreign substances (food, drinks, medications, and supplements) into our mouths hoping that our bodies will be able to sort out friend from foe. And generally, our bodies do a terrific job—even though much of what we put in our mouths was foreign to the environment even 100 years ago. Because of this interface, the digestive system is the seat of ourimmune system, runs our metabolism, makes vitamins, and communicates with every other cell in the body. The purpose of the digestive system, also lovingly called "the gut," is to bring nutrients to each cell of your body. When this doesn't occur, we feel tired and sluggish, can't think clearly, and begin to develop symptoms of illness. If ignored, these symptoms can develop into full-blown health problems. There is currently an epidemic of digestive illness in our country, one that is directly related to the foods we eat and the way we live. Between 30 and 40 percent of us complain about digestive issues, accounting for 104.7 million doctor visits a year. Research into the functioning of the digestive system has yielded surprising results: #1. If spread flat, your digestive system would cover a tennis court. #2. Roughly 70 percent of your immune system is located in the digestive system. #3. You have 10 times as many microbes as cells in your body. These microbes live in communities that live in symbiosis with you. The health of these communities determines your overall health. Collectively, these communities are called the microbiome. #4. You have 100 times more DNA in your microbiome than in the cells of your body. The DNA in your cells and in your microbiome talk to each other. #5. Your microbiome is made up of three-and-a-half to four-and-a-half pounds of bacteria that help to make vitamins, protect you against infection, and run your metabolism. #6. The digestive system is often called the "second brain" because if the vagus nerve, which connects the brain and the digestive system, is cut, the digestive system functions fine on its own. This system is called the enteric nervous system (ENS). #7. Your gut manufactures significantly more neurotransmitters, such as serotonin, than does the brain. In fact, 80 to 90 percent of your serotonin is made in the gut, and every class of brain neurotransmitter has been found in the gut. More From Rodale News: 5 Problems With Over-the-Counter Painkillers #8. You eat food to ultimately nourish all of your cells. If you make poor food choices or if your body cannot digest, absorb, and utilize the food due to poor digestive function, you probably will eventually develop signs, symptoms, and finally a diagnosable illness. #9. Digestive insufficiencies contribute to a wide range of health issues, including migraine headaches, depression, arthritis, foggy thinking, autoimmune illness, autism, fibromyalgia, chronic fatigue, multiple sclerosis, and more. #10. Food talks to your microbiome and to your genes. And finally, foods that are terrific for others may or may not be healthful for you. To help protect this incredible part of your body, learn to avoid thesenine things that kill your gut. And work more of these gut-friendly foods(including dark chocolate!) into your diet.