What breaks down dietary fiber in the digestive system?

Bacterial fermentation is the correct answer because it specifically refers to the process that occurs in the digestive systems of certain animals, such as ruminants and herbivores, where gut bacteria break down dietary fiber. This complex process involves microbial action that converts fibrous plant material into simpler compounds, allowing the host animal to absorb nutrients that they otherwise would not be able to extract from fiber.

In many cases, dietary fibers are resistant to enzymatic digestion by the mammalian digestive system alone due to their complex structure. Instead, bacteria present in the gut carry out fermentation, producing short-chain fatty acids, gases, and other byproducts that the animal can use for energy and nutrition.

Other methods like enzymatic digestion, acid hydrolysis, and mechanical grinding play roles in digestion as well, but they are not specifically responsible for the breakdown of dietary fiber. Enzymatic digestion primarily involves breaking down carbohydrates, proteins, and fats into simpler molecules, whereas acid hydrolysis pertains more to breaking down chemical bonds with the help of acids. Mechanical grinding, such as chewing, aids in physically breaking down food into smaller pieces, which can then be acted upon by enzymes, but it does not chemically break down fiber as fermentation does. Thus, bacterial fermentation is the critical process