英语时差：食物是如何消化的？

The human body is capable of digesting a very wide range of foods, including sugars, fats, and proteins. But the trick to such a varied diet is in the body’s ability to stop digesting when the food’s all gone so that it doesn’t start in on itself. One of the ways the stomach avoids digesting itself involves the body’s careful handling of the strong chemical called protease. Protease is a group of enzymes that break down protein. But since the body itself is made of protein, it’s important that those enzymes don’t go to work on our own bodies. The body produces protease in the pancreas, but the pancreas doesn’t produce protease in a working condition. Instead, the protease produced in the pancreas has to be activated by another enzyme found in the intestine. Only after it is activated by the other enzyme, can the protease go to work breaking down protein. The second, activating enzyme, in turn only does its job when food enters the stomach.