Normal intestinal bacteria are so numerous that you have far more bacteria than the total number of cells in your body. The “good bacteria” in your intestines help to prevent bad bacteria from infecting you, and may help to prevent intestinal diseases such as ulcerative colitis, Crohn’s disease and cancers.
When you eat, enzymes from your intestines, stomach, liver and pancreas break down your food into its building blocks that can be absorbed into your bloodstream. Carbohydrates are broken down into sugars; proteins into amino acids; and fats into glycerol, fatty acids and monoglycerides. However, many foods contain undigestible starches that cannot be broken down into sugars, so they cannot be absorbed in the upper intestinal tract. When they reach the colon, bacteria ferment these undigestible starches to form other chemicals including short chain fatty acids that protect your intestinal lining from irritation and cancer, and are absorbed into your bloodstream to lower cholesterol and prevent heart tacks. Some of these “good” bacteria, such a lactobacillus, are used to ferment and preserve some foods made from milk or plants. Eating live-culture yogurt may help you maintain or increase the number of good bacteria you have in your gut. Not all yogurt contains live bacteria; read the label to make sure yours is “active.”
Various “probiotis” are marketed to help grow healthful gut bacteria; see Probiotics and Prebiotics.