Food and nutrition.pdf

Chapter 4Digestion and AbsorptionDIGESTIONDigestion is the breakdown of food into smaller particles or individualnutrients. It is accomplished through six basic processes, with the help ofseveral body fluids-particularly digestive juices that are made up ofcompounds such as saliva, mucus, enzymes, hydrochloric acid,bicarbonate, and bile.The six processes of digestion involve:• The movement of food and liquids;• The lubrication of food with bodily secretions;• The mechanical breakdown of carbohydrates, fats, and proteins;• The reabsorption of nutrients-especially water;• The production of nutrients such as vitamin K and biotin byfriendly bacteria; and• The excretion of waste products.Comprehension of the tasks or processes needed to break down foodare essential to an understanding of how and when food really begins tofunction within the body. For example, not understanding thatcarbohydrates break down into glucose could lead one to believe that thebest source of glucose is in liquid form such as a soft drink. This couldcause one to miss out on the nutrients (and great taste) in fruits, vegetables,and grains. Likewise, not understanding the digestion process could leada person to believe in the myth of "food combining," or perhaps to thinkit is normal to be hungry all the time. But, in fact, the digestive processesnormal to human physiology can simultaneously handle carbobydrates,fats, and proteins-and allow people to go several hours between meals,especially if meals are balanced in fibre and the individual nutrientsneeded.GI Tract PhysiologyDigestion begins in the mouth with the action of salivary amylase.The food material then progresses past the esophagus and into the