Carbohydrates

Carbohydrates- Compounds made of single sugars or multiple sugars and composed of carbon, hydrogen, and oxygen atoms (carbo = carbon, hydrate = water).  Primary role of carbohydrates is to provide  the body with energy (calories).  They are almost exclusively obtained from plants.  Milk is the only animal derived food that contains significant amounts of carbohydrate.

Complex Carbohydrates- Long chains of sugars (glucose) arranged as a starch or fiber; also called polysaccharides (poly = many; saccharide = sugar unit).

Simple Carbohydrates- Single sugars (monosaccharides) and the pairs of sugars (disaccharides) linked together.  Polysaccharides are long chain of 10 or more glucose molecules linked together in straight or branched chains.

Glucose- The building block of carbohydrates; a single sugar used in both plant and animal tissues as quick energy.  All carbohydrates can be converted to glucose except fiber. 

Glucose is the preferred energy source for the brain and nervous system.  In the presence of chlorophyll and the enrgy of the sun, plants make glucose through a process known as photosynthesis.  Water is absorbed by the plants roots and CO2, absorbed through the plants leaves, combine to form a molecule of glucose.  Glucose is not a very sweet sugar, but plants can rearrange its atoms to form another sugar, fructose, which is sweet to the taste.

Cells cannot use the lactose, sucrose, or starch -they require glucose.  The task of the digestive system is to disassemble the double sugars and starch into single sugars so that these these monosaccharides can be absorbed into the blood.  Following absorption, the liver converts to glucose any carbs that were not absorbed in the form of glucose, so they can be used by the cells.  The cells can either store the glucose use it for current energy needs, or convert it to fat.

Enriched- Referes to the process by which the B vitamins thiamine, riboflavin, niacin, folic acid and the mineral iron are added to refined grains and grain products at levels specified by law.

Fortified – Term for foods to which nutrients have been added.

Whole Grain- Refers to a grain that only has its husk removed.  These include wheat, corn, rice, rye, oats, amaranth, barley, buchwheat, sorghum, and millet.

Refined- Refers to the process by which the coarse parts of food products are removed.  For example, refining wheat into flour involves removing 3 of the 4 parts of the kernel, the chaff, bran and the germ.  Only leaving the endosperm.

Fiber – The indigestible residues of food, composed mostly of polysaccharides.  The best known of the fibers are cellulose, pectin and gums.  The bonds that hold the units of fiber together cannot be broken by human digestive enzymes but some can be broken down by the bacteria that reside in the human digestive tract.  Very few (if any) calories are absorbed during the process.

Insoluble Fiber- Includes the fiber types called cellulose, hemicellulose, and lignin.  Insoluble fibers do not dissolve in water.

Soluble Fiber- Includes the fiber types called pectin, gums, mucilages, some hemicelluloses and agal substances (for example carrageenan).  Soluble fibers either dissolve or swell when placed in water.

Benefits of Fiber- Insoluble fiber holds water in the colon, thereby increasing bulk and stimulating the muscles of the digestive tract so that they retain their health and tone.  It appears that the products of bacterial digestion soluble fiber in the colon are absorbed into the body and may inhibit the bodies production of cholesterol, as well as enhance the clearance of cholesterol from the blood.

Summary of Carbohydrate Digestion and Absorption

Carbohydrate digestion begins in the mouth.  The salivary glands secrets a watery fluid into the mouth to moisten the food.  An enzyme begins digestion by splitting starch into smaller polyssaccharides and maltose.  This digestion continues until stomach acid and enzymes start to digest the salivary enzymes.

Next, the pancreas produces carbohydrate digesting enzymes and releases them through the common bile duct into the small intestine.  These enzymes split polysaccharides into disaccharides.  These enzymes on the surface of the cells of the small intestine break these into simple sugars.  Absorption of the monosaccharides takes place in the small intestine.

These simple sugars are then absorbed into the blood and travel to the liver; the liver regulates the amount of glucose circulating in the blood in response to the hormones insulin and glycagon.

Finally, most of the fiber passes intact through the digestive tract through the large intestine and is eventually excreted with feces.

Read more about the cycle here.