Digestion, Absorption, and Metabolism of the Macronutrients Carbohydrate, Protein, and Fat

(Image: By OpenStax College)

Digestion and absorption is the way in which the body receives nutrients. “The macronutrients are the large (macro) molecules in food that provide our body with energy. The necessary mac-ronutrients: carbohydrate, protein and lipid each yield stored energy when released,” (MSJC 2015).

Digestion begins in the mouth and then moves through the major digestive organs: pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus. The accessory digestive organs teeth, tongue, salivary glands, pancreas, liver and gall bladder aid in digestion (Johnstone, Hendry, Farley & McLafferty 2014). Each of these organs work to extract nutrients from food for use in the body.

Digestion of micro- and macronutrients begins in the mouth. The teeth work to break down the food into smaller pieces for easier digestion. Enzymes in saliva also break down food, and the water in saliva moistens the food (bolus) so it is easier to swallow and pass down the esophagus into the stomach (Sizer, Whitney 2014).

In the stomach and intestines acids liquefy and further break down the bolus through a squeezing action called peristalsis. The bolus is held and liquefied in the top part of the stomach and passed a little at a time to the lower stomach and intestines where it becomes chime. By the time the bolus has reached the small intestine proteins and starches have begun to break down and fats have separated. At this point, carbohydrates can continue to be broken down to provide more energy, or they can become building blocks of protein or units of fat (Sizer, Whitney 2014).

Most fat digestion takes place in the small intestine, at which time bile from the gall bladder emulsifies fat preparing it for enzyme action. Fatty acids are then absorbed by intestinal villi and enter into the blood stream. The small amount of cholesterol that reaches the large intestine becomes trapped in fiber and exits the body during elimination (Sizer, Whitney 2014).

Protein digestion begins in the mouth with chewing and saliva, however, in the stomach, stomach acid alters protein by uncoiling the strands to better enable enzymes to attack the peptide bonds. In the small intestine, alkaline pancreatic juices neutralize stomach acid allowing enzymes to break down larger strands of protein. After protein is broken down, cells of the small intestine absorb amino acids and send them to the blood stream where amino acids are dispatched to the body’s cells (Sizer, Whitney 2014). Any product that cannot be used will be released from the large intestine in 18-24 hours (Johnstone, Hendry, Farley & McLafferty 2014).

Micro- and macronutrients are important to digestion and maintaining health. The body requires nutrients to perform essential bodily functions, including aiding in digestion. Individuals who would like healthy sweet and savory recipes can go here.



References:

By OpenStax College (n.d.). [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

Johnstone, C., Hendry, C., Farley, A., & McLafferty, E. (2014). The digestive system: part 1. Nursing Standard, 28(24), 37-45.

Melanie. (2015). Nutritious eats. Retrieved from http://www.nutritiouseats.com/

MSJC. (2015). Digestion, absorption and macronutrients. Retrieved from http://www1.msjc.edu/hs/nutr100/nutr100_section2a.html

Sizer, F., Whitney, E. (2014). Nutrition: Concepts and Controversies, 13e, 13th Edition. Cengage Learning. VitalBook file.