Digesting Macronutrients

            Without the digestive tract, the human body would be unable to absorb the nutrients needed from the foods ingested. The digestive tract is made up of the mouth, stomach, small intestine, and the colon. Each of these sections has a function that allows the human body to break down and absorb the macronutrients and discard what it cannot take in. For our bodies to metabolize macronutrients (carbohydrates, fats, and protein) in our food, we first need to ingest it. 

            The digestive process begins at the mouth with chewing that releases saliva and its enzymes. Each of these enzymes breaks down a different form of macronutrient. Once the food has passed through the mouth into the stomach, there are even more enzymes, with the addition of water and hydrochloric acid. These break down the food into a liquefied form. Without this stomach acid to aid in the breakdown, the food would not be able to pass through to the small intestine. Within the intestines, there are bacteria, bile from the gallbladder, and bicarbonate from the pancreas to help neutralize any of the stomach acids that had made its way into the intestinal tract with the liquefied food. While humans eat a broad “range of bacteria, yeasts, and molds in our food and water; some of these microbes can be harmful if they survive and flourish” (Martin, 2006. Page 45, para 2). 

Digesting Carbohydrates

 

            When it comes to the digestion of carbohydrates, the process starts as soon as it mixes with saliva and the enzymes it contains. After leaving the mouth, the breaking down and digestion process continues in the stomach until it is mixed with hydrochloric acid, which stops the process of digestion. Once inside of the small intestine, an enzyme from the pancreas along with enzymes from the intestinal lining break the starch fragments into sugars that can then be absorbed. Anything left over after this process goes through to the large intestine where it gets mixed with intestinal bacteria. (Sizer & Whitney, 2013).  After this final process, any indigestible fibers left over are excreted. 

Digestion of Fats

           

            Unlike the process that happens with carbohydrates, only a small amount of fat is broken down within the mouth.  Even less fat is broken down while in the stomach since it floats on top of the watery stomach fluid. Because of this, fat is the last of the contents to leave the stomach for the small intestine. Once the fat reaches the small intestine, bile, and fat digesting enzymes break down fat molecules into fatty acids. From this state, it can be absorbed. However, as with all other substances going through the intestines, some do not and are excreted.

Digestion of Protein

            While it is harder for the body to break down and absorb fats than it is carbohydrates, it is the protein that takes the longest to break down. As with all foods, the digestion and absorption of nutrients from protein starts with the mouth. After the protein is softened and mixed with saliva, it makes its way to the stomach where it is combined with stomach acid, thus breaking it down further. Once the protein makes its way to the small intestine, it is met with more enzymes as well as digestive juices from the intestines and the pancreas. These juices and enzymes break the protein into smaller pieces. (NIDDK, 2013). While some of the proteins are absorbed in the small intestine, it is in the colon with its beneficial bacteria where “almost all food protein is digested and absorbed” (Sizer and Whitney, 2013).
            As it can be seen, while the macronutrients of carbohydrates, fat, and protein go through the same systems in the process of digestion, how they are absorbed is very different. Without these processes, we would not be able to obtain the nutrients we need from the foods we eat.    

           

References

Martin, B. (2006).  How Digestion Works. Total Health, 28(3), 44-51. Retrieved from EBSCOhost.

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