Why does it take longer to digest protein than fats or carbohydrates?

Of all the food categories, the digestion of proteins is the most time consuming. It takes over three hours to break down and assimilate proteins. The reason for this is simple: protein molecules are long chains with well-soldered links, and to break down their resistance requires the combination of good chewing and the simultaneous attack of various gastric, pancreatic, and biliary juices.

This long process of calorie extraction taxes the system; it has been calculated that to obtain 100 calories from a protein food, the system must use 30 calories. We can say that the specific dynamic action of proteins is 30 percent, while it is only 12 percent for fats and just 7 percent for carbohydrates.