Written by Dr. Shalini Aul, MBBS, DND | 
Article Reviewed by Dietitian julia samuel, M.Phil on Jul 18, 2018

Structure and Functions of Carbohydrates

Carbohydrates, as the name suggests, refers to the hydrates of carbon comprising carbon, hydrogen and oxygen. The hydrogen and oxygen present in carbohydrates is in the ratio of 2:1. Carbohydrates are also divided, according to chemical structure, into monosaccharide’s (a single saccharide), disaccharides (two single saccharides), oligosaccharides and polysaccharides. The molecular weight of monosaccharide’s and disaccharides are relatively smaller classifying them into simpler sugars such as glucose and fructose (found in honey and fruits).

Two monosaccharide’s join together to form a disaccharide which is the simplest of polysaccharides with respect to structure e.g., sucrose (table sugar) and lactose or galactose (produced by the digestion of milk).

Monosaccharides do not require enzymes for absorption by the small intestines.

Polysaccharides are larger molecules made by combining many monosaccharide units together, and serve to store energy (e.g., glycogen and starch). The intestine is unable to absorb polysaccharides because they are too large, so they require enzymes produced in the small intestine to break it down into monosaccharide units.

Following are the functions of carbohydrates:

  • Monosaccharides are important bimolecular substances necessary for normal development of life. They help the immune system to function, facilitate fertilization and formation of the DNA and also play a role in the prevention of any pathogenesis.
  • The 5-carbon ribose (a monosaccharide) is necessary for the formation of important co-enzymes such as ATP, FAD and NAD, which supply the energy requirements of the body. Ribose is also required to make the RNA (ribonucleic acid) as well as the DNA (deoxyribonucleic acid) for the genetic structure of an individual as they are the building blocks of nucleic acids.
  • Carbohydrates are imperative as a source of energy. They leave the proteins free to be used as a building block of the body.
  • Insufficient carbohydrates in the diet leads to the breakdown of fats as a source of energy and the accumulation of ketone bodies in the blood causing a condition known as “ketosis”.
  • Carbohydrates are the singular source of energy for the brain! They also play an important role in the regulation of the nervous system.
  • High fiber carbohydrates prevent bowel irregularities like constipation and prevent development of diseases such as diabetes, cancer and heart diseases.

Certain carbohydrates promote the development of healthy bacteria in the digestive system.

  • Polysaccharides make up the structural complex of cellulose in plants and the chitin present in arthropods, besides storing energy as glycogen in liver and muscle cells, and starch in plants.


  1. Lanfer A, Hebestreit A, Ahrens W. Diet and eating habits in relation to the development of obesity in children and adolescents - (http://www.ncbi.nlm.nih.gov/pubmed/20631972)
  2. Guerreiro S, Alçada M, Azevedo I. Sugary drinks and glycemia - (http://www.ncbi.nlm.nih.gov/pubmed/20687984)
  3. Astrup A, Meinert Larsen T, Harper A. Atkins and other low-carbohydrate diets: hoax or an effective tool for weight loss? Lancet. 2004;364(9437):897–899. [PubMed]
  4. Wurtman RJ, Wurtman JJ. Brain serotonin, carbohydrate-craving, obesity and depression. Obes Res. 1995 Nov;3 Suppl 4:477S-480S - (http://www.ncbi.nlm.nih.gov/pubmed/8697046)
  5. van Dam RM, Seidell JC Carbohydrate intake and obesity. Eur J Clin Nutr. 2007 Dec;61 Suppl 1:S75-99 - (http://www.ncbi.nlm.nih.gov/pubmed/17992188)
  6. Drewnowski A, Kurth C, Holden-Wiltse J, Saari J. Food preferences in human obesity: carbohydrates versus fats - (http://www.ncbi.nlm.nih.gov/pubmed/1510463)
  7. Foster GD, Wyatt HR, Hill JO, McGuckin BG, Brill C, Mohammed BS, Szapary PO, Rader DJ, Edman JS, Klein S A randomized trial of a low-carbohydrate diet for obesity.
  8. Crapo, P. A., Reaven, G., Olefsky, J. (1976) Plasma glucose and insulin responses to orally administered simple and complex carbohydrates. Diabetes 25: 741–747.
  9. Jenkins, D. J., Wolever, T. M., Taylor, R. H., et al (1981) Glycemic index of foods: a physiological basis for carbohydrate exchange. Am J Clin Nutr. 34: 361–366.
  10. Joint FAO/WHO Expert Consultation (1998) Carbohydrates in human nutrition (FAO Food and Nutrition Paper 66) FAO Rome, Italy.
  11. Bell, S. J., Sears, BS. (2003) A proposal for a new national diet: a low-glycemic load diet with a unique macronutrient composition. Metab Syndrome Rel Disord. 1: 199–208.
  12. Bell, S. J., Sears, B. (2003) Low-glycemic-load diets: impact on obesity and chronic diseases. Crit Rev Food Sci Nutr. 43: 357–377. | Article | PubMed | ISI |
  13. Brand-Miller, J. C., Holt, S. H. A., Pawlak, D. B., McMillan, J. (2002) Glycemic index and obesity. Am J Clin Nutr. 76(suppl): 281S–285S. | PubMed | ISI | ChemPort |
  14. Sandrou, D. K., Arvanitoyannis, IS. (2000) Low-fat/calorie foods: current state and perspectives. Crit Rev Food Sci Nutrition. 40: 427–447.
  15. Ludwig DS. The glycemic index - Physiological mechanisms relating to obesity, diabetes, and cardiovascular disease. JAMA 2002; 287: 2414-2423
  16. Ludwig DS. The glycemic index - Physiological mechanisms relating to obesity, diabetes, and cardiovascular disease. JAMA 2002; 287: 2414-2423
  17. Das SK, Saltzman E, Gilhooly CH, DeLany JP, Golden JK, Pittas AG, Dallal GE, Bhapkar MV, Fuss PJ, Dutta C, McCrory MA, Roberts SB. Low or moderate dietary energy restriction for long-term weight loss: what works best?Obesity (Silver Spring). 2009 Nov;17(11):2019-24. Epub 2009 Apr 23.
  18. Atkins, Robert (2003-09-25). Dr. Atkins'' New Diet Revolution, Revised Edition. .Evans. ISBN 978-1590770023.

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