Fiber explained
Fiber is an indigestible carbohydrate. Human lack the enzymes needed to convert fiber to sugar(although other organisms do this quite well, such as some bacteria.)
Even though we can’t use fiber as a source of energy, fiber is an important nutrient, because it has a significant impact on the absorption of other, digestible carbohydrates. Fiber also has an effect on our digestion and elimination, and a major impact on the types of bacteria living and growing in our intestines, which can and do utilize fiber as a food source.
There are two main categories of fiber: soluble and insoluble.
The terms soluble and insoluble simply indicate whether a fiber can be digested or not.
For example, bran is an insoluble fiber, It cannot be broken down by the body. This increases the bulk of stool and the speed with which you eliminate waste, and may also cause absorption of toxins.
Soluble fiber comes most often from non wheat types of fiber, such as from fruits or vegetables, and is broken down by the beneficial bacteria in your gut; these bacteria rely on soluble fiber as their own food source. Generally, the more soluble fiber in your diet, the more you promote the growth of healthy bacteria in the colon. These bacteria are considered beneficial because in the process of breaking down soluble fiber, they produce by-products (vitamins) that are important for out health.
That’s one of the reason we should be careful to use antibiotics because it not only induce tolerance for the “bad bacteria” and it also kills “good” bacteria.