The digestive system is a series of hollow, tubular structures running from the mouth to the anus. It includes the esophagus, stomach, small intestine, and large intestine. As food travels though this system, it is broken down into small units that are absorbed by the lining cells of the intestine and transported into the bloodstream.
If the digestive system is to function properly, it must work in coordination with other internal organs, the liver, which produces bile, the gallbladder, which stores bile, and the pancreas, which produces digestive enzymes.
Digestion transforms fats into fatty acids and glycerol, proteins into amino acids, and carbohydrates into simple sugar, all to be used by the body as energy or as chemical building blocks. If a person overeats, all of the nutrients not used as energy or for maintaining body structure and function can be converted into body fat.
Digestive enzymes, found mostly in the liver and the pancreas, are chemicals manufactures in the body that help break down food into its nutrient components.
The energy we get from food is measured in calories, a unit that refers to the amount of heat necessary to raise one gram of water one degree centigrade. Saying that a portion of food has 250 calories means that when the food is digested and absorbed, it provides 250 calories worth of energy that the body can use.
The number of calories an individual needs to maintain daily activity depends on the person’s size, level of physical activity, and health. When inflammation is present, heat is being generated and more calories are being used, calories are also being burned by fever. Hence fighting inflammatory bowel disease actually requires a higher intake than a healthy person needs.