Digestion, Absorption, and Metabolism of Macronutrients

Macronutrients are carbohydrates, protein, and fats.  The first step with all of the macronutrients is to consume them and this starts with the chewing process.  When the food is chewed and swallowed the digestion process has started.  Interactive process of digestion is a great interactive tool that allows you to pick different foods that the body consumes to see how the digestion process works with those foods.  When food is introduced in the mouth it is chewed and saliva is mixed with the food to help break it down.  Once the food is chewed up, it is then swallowed and passes through the esophagus and into the stomach.  "In the stomach, protein digestion begins.  Cells in the stomach release gastric juice, a mixture of water, enzymes, and hydrochloric acid.  This strong acid mixture is needed to activate a protein-digesting enzyme and to initiate digestion of protein" (Sizer & Whitney, 2013 p.86).  The partially digested food is then passed from the stomach into the intestines.  In the intestines, bile is released to help with fat absorption and as the partially digested food is passed through the intestines, minerals and vitamins are absorbed.  Once the nutrients are absorbed to be used by the body the rest of the food is considered waste and it passes through the colon.  The end result of digestion is the waste exiting the body by way of the anus.  This cycle happens every time food is introduced into the body.

Each macronutrient is digestion and absorbed differently.  Carbohydrates are broken down to form glucose.  Foods that are made up of whole grains or foods full of fiber are slowly digested and are absorbed steadily in the body causing the body to fill fuller longer.  Those foods that consist of refined grains are quickly absorbed and causes a quick increase in blood sugar and then a quick drop and leaves you feeling hungry sooner.  Carbohydrates are digested and form glucose for the body to use as energy.  If the body consumes to many carbohydrates, then the body stores the excess glucose as fat in the body. 
Digestion of protein uses the stomach acid to help break the protein down.  It is then passed into the small intestines to be absorbed and used by the different organs.  "When a person eats food proteins, whether from cereals, vegetables, beef, fish, or cheese, the body must first alter them by breaking them down into amino acids; only then can it rearrange them into specific human body proteins" (Sizer & Whitney, 2013 p. 205). 
Fats are digested with the help of bile which breaks fat down and helps the body to absorb it in the intestines.


References

Kitses, J. (2008, January 1). . . Retrieved June 19, 2014, from http://kitses.com/animation/swfs/digestion.swf

Sizer, F. & Whitney, E. (2013).  Nutrition: Concepts and Controversies (13th ed.).  Mason, OH: Cengage Learning.