Physiology, Carbohydrates

In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan.


Carbohydrates are one of the three macronutrients in the human diet, along with protein and fat. These molecules contain carbon, hydrogen, and oxygen atoms. Carbohydrates play an important role in the human body. They act as an energy source, help control blood glucose and insulin metabolism, participate in cholesterol and triglyceride metabolism, and help with fermentation. The digestive tract begins to break down carbohydrates into glucose, which is used for energy, upon consumption. Any extra glucose in the bloodstream is stored in the liver and muscle tissue until further energy is needed. Carbohydrates is an umbrella term that encompasses sugar, fruits, vegetables, fibers, and legumes. While there are numerous divisions of carbohydrates, the human diet benefits mostly from a certain subset.


Monosaccharide: The most basic, fundamental unit of a carbohydrate. These are simple sugars with the general chemical structure of C6H12O6.

  1. Examples: glucose, galactose, fructose

Disaccharide: Compound sugars containing two monosaccharides with the elimination of a water molecule with the general chemical structure C12H22O11

  1. Examples: sucrose, lactose

Oligosaccharide: The polymer contains three to ten monosaccharides

  1. Examples: maltodextrins, raffinose

Polysaccharides: Polymers containing long chains of monosaccharides connected through glycosidic bonds

  1. Examples: amylose, cellulose


Simple Carbohydrates: One or two sugars (monosaccharides or disaccharides) combined in a simple chemical structure. These easily are utilized for energy, causing a rapid rise in blood sugar and insulin secretion from the pancreas.

  1. Examples: fructose, lactose, maltose, sucrose, glucose, galactose, ribose

  2. Foods: candy, carbonated beverages, corn syrup, fruit juice, honey, table sugar

Complex Carbohydrates: Three or more sugars (oligosaccharides or polysaccharides) bonded together in a more complex chemical structure. These take longer to digest and therefore have a more gradual effect on the increase in blood sugar.

  1. Examples: cellobiose, rutinulose, amylose, cellulose, dextrin

  2. Foods: apples, broccoli, lentils, spinach, unrefined whole grains, brown rice

Starches: Complex carbohydrates contain a large number of glucose molecules. Plants produce these polysaccharides.

  1. Examples include potatoes, chickpeas, pasta, and wheat.

Fiber: Non-digestible complex carbohydrates that encourage healthy bacterial growth in the colon and act as a bulking agent, easing defecation. The main components include cellulose, hemicellulose, and pectin.

  1. Insoluble: Absorbs water in the intestines, thereby softening and bulking stool. Benefits include regularity of bowel movements and a decreased risk of diverticulosis.

    1. Examples: brans, seeds, vegetables, brown rice, potato skins.

  2. Soluble: Helps decrease blood cholesterol and LDL levels, reduces straining with defecation, and blunts postprandial blood glucose levels.

    1. Examples are fleshy fruit, oats, broccoli, and dried beans.

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