How do Enzymes help Digestion?

This is an important consideration when considering enzymes. First, amylase is contained in everyone's saliva. Amylase is the enzyme that breaks down carbohydrates. When you chew carbs/breads, it becomes sweeter as you chew because the mechanical action of your teeth and amylase in the saliva are breaking the carbohydrates down to their component sugars. Next, the foods goes to the stomach where it resides about 60 minutes or more as it is further digested by the stomach acid and pepsin. Pepsin is a protease enzymes released into the stomach. There is more mechanical breakdown too by the stomach muscles. If you take plant enzymes, most plant enzymes are quite stable in the stomach environment and go to work. This gives the plant enzymes an edge on digestion over animal/pancreatic enzymes. Plant enzymes can be working on food for at least an hour before the food proceeds to the small intestine. Once the food enters the small intestine, plant enzymes continue to work. At this point, any pancreatic or animal enzymes kick in. It is at this point that your naturally produced pancreatic enzymes are released by the pancreas. Some enzymes are released by the small intestine lining as well.
The enzymes from the small intestine include:
lactase (breaks down milk sugar),
DPP IV (breaks down milk protein and other protein bonds), and
dissacharrides (breaks down some starches and sugars).
Anything that disrupts the small intestine may also disrupt the production and release of these enzymes. If you have a leaky gut, inflammation, yeast, or something else which hampers the small intestine, then you are likely to also have trouble digesting the foods these enzymes work on.
So any time the gut lining gets injured, these enzymes may not be available for digesting food. An injured gut can also become 'leaky'. Thus the food not digested can become a problem. So it is rather the gut is injured and digestion in interrupted, and not that the food is the problem to begin with. One strategy is to take out all offending foods (i.e a gluten-free/casein-free diet or GFCF), however, the gut will still be injured in this case and ANYTHING you eat can become a problem because the 'new' foods substituted in may also be insufficiently digested as well. This is why people who think they are starting a GFCF diet end up slowly taking out 28 other main foods as well. The strategy of the Specific Carbohydrate Diet is that all foods requiring these enzymes are eliminated until the gut heals. Then you can return to eating those foods again. Another strategy is to take measures to proactively heal the gut. A direct way to heal the gut is with digestive enzymes, but there are also other supplements that help too. Enzymes help heal the gut for a number of reasons that have been proved clinically. Once the gut lining heals, the cells in the lining 're-grow' and your natural digestive enzymes start producing again. Thus the once problematic foods are now not a problem.