When you consume food, your digestive tract breaks down the components of the food you eat into molecules that your intestine can absorb into the bloodstream. Cells then take up the products of digestion, and use them for cellular energy needs or to build a variety of molecules.
The purpose of the digestive tract is to extract the molecules of nutrition from the food you eat. Carbohydrates -- including sugar and starch -- in your food break down into sugars that the intestine absorbs. Your digestive tract breaks protein down into molecules called amino acids. Finally, fat breaks into three pieces -- two fatty acids and one chemical called a monoacylglycerol -- that the intestine absorbs and then reassembles into fat. Your cells can then pull the molecules of nutrition out of the bloodstream after they are absorbed.
Features of Digestion
Digestion in the human body has to take place in a timely manner -- the digestive tract moves food through mechanically using muscular contractions of the stomach and intestine. As such, digestive chemicals have to work quickly to ensure breakdown of large molecules into nutrients that the small intestine can absorb. For this reason, your digestive tract relies upon enzymes, which are chemicals that help otherwise slow reactions take place faster, explain Drs. Mary Campbell and Shawn Farrell in their book "Biochemistry."
Digestive Enzyme Types
Specific digestive enzymes have different roles in the body. Enzymes called amylases break down carbohydrates, while proteases break down proteins. Lipases work together with bile salts to break down fat. In the intestine, specific enzymes break down small sugars called disaccharides into even smaller sugars, called monosaccharides. There is a different type of digestive enzyme for each disaccharide, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
Secretions of the mouth, stomach, pancreas, liver and small intestine contain the enzymes and other molecules needed to break down foods for absorption. The epithelial cells that line the inner layer of the small intestine take up the breakdown products of digestion reactions. In her book "Human Physiology," Dr. Lauralee Sherwood explains that the absorption mechanism for sugar is similar to that for amino acids, but that fats move passively across the intestinal lining.
Different foods digest -- and the small intestine absorbs their breakdown products -- at different rates, explains Sherwood. In general, carbohydrates are much faster to digest than proteins, which digest faster than fats. High-fiber carbohydrates digest and are absorbed more slowly than refined, or low-fiber carbohydrates. This is the reason that whole grains make you feel full longer than refined grains or sugar -- they digest more slowly and spend a longer period of time in the gut.
- Biochemistry; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.
- Biochemistry; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.
- Human Physiology; Lauralee Sherwood, Ph.D.
- Lara Hata/Photodisc/Getty Images
This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or JillianMichaels.com.