Your digestive system is home to billions of bacteria. Most of them are harmless, and many actually keep you healthy. These good guys are known as probiotics, and you need them to digest food, fight off illness, and maintain a healthy gut. These beneficial organisms have antibiotic and anti-inflammatory powers. They kill infectious bacteria and protect the delicate lining along your digestive tract from attack by disease-causing organisms. They even boost the immune system by helping your body make antibodies and phagocytes, germ-killing cells.