What are carbohydrates? Is fiber a carb?

What are carbohydrates? Is fiber a carb? 

By Daniel Rocha LMT CPT CNS


Carbohydrates consist of carbon, hydrogen, and oxygen. Complex carbohydrates, such as starch and fiber, are categorized as polysaccharides. Simple carbohydrates or sugars are classified as mono-or disaccharides. Monosaccharides consist of only one sugar molecule and include glucose, fructose, and galactose. Disaccharides have two sugar molecules bonded together and include lactose, which is made of glucose and galactose; maltose, made of two glucose units; and sucrose, made of glucose and fructose. Monosaccharides are absorbed directly into the bloodstream, but disaccharides must be broken down into monosaccharides before they are absorbed. Both simple and complex carbohydrates provide about four calories per gram and are converted by the body to glucose, 


When food is consumed, the digestion begins in the mouth, where saliva breaks down starch into disaccharide maltose. The food then moves to the stomach, mixed with the stomach's acid and other juices. In the small intestine, starch is broken down further into disaccharides. An enzyme released from the pancreas breaks down small polysaccharides. Cells lining the small intestine secrete an enzyme dividing disaccharides and polysaccharides into monosaccharides. These monosaccharides are absorbed then taken to the liver. The liver converts fructose and galactose to glucose. Excess fructose or galactose is converted to fat. Glucose is transported by the circulatory system and used for energy.


Complex carbohydrates (starches) break down slower than simple carbohydrates, raising blood glucose levels more slowly than simple carbohydrates. This concept is known as the glycemic index and glycemic load. Eating more significant amounts of complex carbohydrates causes blood glucose levels to fluctuate less, aiding individuals with non-insulin-dependent type 2 diabetes. The Harvard Medical School developed an eating pyramid that accounts for the glycemic index of many foods.


Excess glucose in the blood is converted to glycogen stored in the muscle and liver. The liver can be released glycogen into the bloodstream for the brain or other organs. When blood glucose levels decline, the body breaks down glycogen, using it for energy.



Dietary fiber is a group of indigestible carbohydrate-based compounds found in plants. Two types of fiber include insoluble fiber and soluble fiber.


Insoluble dietary fiber from the plants moves through the digestive undigested, and it does not provide energy. The fiber adds bulk to the waste (stool or feces) in the large intestine (colon). Insoluble fiber binds to bile acids, reducing fat and cholesterol absorption. Increased bulk causes the intestine walls to contract rhythmically (peristalsis), causing waste to move through the large intestine more rapidly. In the colon, water in digested food is reabsorbed into the body, and waste is eliminated. If waste passes through the colon rapidly, less water is reabsorbed. The stool will remain soft and moist, making it easy to expel without straining. Sources of insoluble fiber include wheat bran, whole grains, and brown rice.


Soluble fiber is found dissolved in water inside plant cells and is not digested or provides energy. It may be consumed by bacteria that live in the digestive tract. Soluble fiber helps decrease low-density lipoprotein (LDL) cholesterol or “bad” cholesterol. It is found in barley, fruit, legumes, and oats. In water, soluble fiber forms a gel-like substance, where it absorbs water and keeping stool soft. Fiber aids in weight control by displacing calorie-dense fats and promotes fullness. The recommended intake of fiber ranges from 27 to 40 grams per day.



Gourley, L. M., Schenker, S., & Davidson, T. (2021). Carbohydrates. In B. Narins (Ed.), The Gale Encyclopedia of Senior Health: A Guide for Seniors and Their Caregivers (3rd ed., Vol. 2, pp. 513-515). Gale. https://link.gale.com/apps/doc/CX8080300160/HWRC?u=lirn33148&sid=HWRC&xid=9ae5ad70

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