Protein Digestion and Metabolism
The digestion of protein begins in the mouth with chewing. Chewing not only makes food easier to swallow, it also helps with digestion by chopping food up into smaller bits. Remember that it really is important to chew your food thoroughly; don't gulp your food down in huge bites.Protein digestion continues in the stomach with the release of hydrochloric acid and pepsinogen. Hydrochloric acid converts pepsinogen into pepsin, which begins to break down the bonds between the amino acids. This process takes place while the muscles surrounding the stomach squeeze and squish the foods and stomach fluids together.
The next step occurs in the small intestine where the hydrochloric acid is neutralized with bicarbonates released from the pancreas. The pancreas also releases an enzyme called trypsin. Trypsin continues to break apart the amino acids, which are then absorbed into the blood stream. Once in the bloodstream, the amino acids are carried to the cells in various parts of your body. Your body uses the individual amino acids that were broken down during digestion to build the proteins needed for the various functions.
You may not think of protein as an energy source, but proteins do contribute calories to you diet. Those calories need to be acknowledged if you are watching your weight. Each gram of protein you eat has four calories. As this sample menu shows, the USDA suggests that you get about 15% to 20% of your calories from protein. For someone who needs 2000 calories per day, that would equal 75 to 100 grams of protein.
It isn't difficult to get enough protein in your diet. One chicken leg alone will provide you with about 30 grams of protein. One salmon fillet has about 40 grams of protein, a cup of oatmeal has six grams of protein, and a cup of asparagus even has two grams of protein. Since most people get enough protein from their diet, protein deficiency is rare in developed countries. In underdeveloped countries, protein deficiency is more common. Severe protein deficiency is called kwashiorkor. Children with kwashiorkor tend to have very thin arms and legs and large, distended bellies. Lack of protein can cause growth failure, loss of muscle mass, a depressed immune system, lung problems, heart problems, and death.
This Week's Assignment
This week I want you to pay attention to the types of protein you eat every day. You will learn about choosing healthy protein sources next week, so right now I want you to keep track of the types of meat, nuts, seeds, legumes, eggs, dairy, cheeses, fish and seafood you eat. Make note of how they are prepared and how much you eat every day.This Week's Quiz
You can test your knowledge of proteins with this quiz: Quiz Three - Proteins, Amino Acids and MetabolismThis is lesson three of the basic nutrition - macronutrients e-course. Up next, lesson four is about choosing healthy proteins. You may sign up for the whole e-course at Basic Nutrition - Macronutrients
Sources: "Protein." Nutrition Source, Harvard School of Public Health. March 20, 2007.
"USDA National Nutrient Database for Standard Reference." USDA Agricultural Research Service. March 20, 2007.
"Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids." Institute of Medicine of the National Academies. September 05, 2002.
Gropper SS, Smith JL, Groff JL. "Advanced Nutrition and Human Metabolism." Fourth Edition. Belmont, CA. Wadsworth Pub Co. 2005.
