The only thing that can cause an enzyme to loose effectiveness is either an enzyme inhibitor, a major pH change or extreme high temperatures. Plus, you have about 15 different enzymes that break down different types of molecules (fat, sugar, protein) located in different areas throughout your digestive system. You start breaking down carbs in your mouth, protein in your stomach and fats and nucleic acids make it all the way to your small intestine before they start to break down.

In your stomach, the digestive enzyme is pepsin, which is kind of "self activating." It's secreted as an inactive enzyme, pepsinogen (inactive so it doesn't eat away the lining of your stomach when it's not in use). Other cells in your stomach secrete hydrochloric acid, as needed, which activates the pepsinogen, turning it into pepsin. The pepsin can then activate more pepsinogen until there is enough to digest all the food, then the process shuts itself off. Several of the other digestive enzymes function this way, as well. Therefore, if the become to "dilute," they can create more as needed.

My advice: drink when you want to