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Polysaccharides – A definition and examples

Polysaccharides are one of the most abundant carbohydrates found in the everyday foods we consume. They are made up of multiple smaller components called monosaccharides bound together with glycosidic bonds. Polysaccharides play a range of roles in the human body too, from energy storage to structural elements for cell membranes and sending cellular messages around the body. Some examples of polysaccharides in plants are starch and cellulose, and chitin in insects. 

What function do polysaccharides serve in the body?

Different polysaccharides will have different functions in humans, plants and animals. Some polysaccharides act as an energy source whilst others store energy in the body for later use. Some help food move through the digestive tract and others help some animals create hard, outer shells or exoskeletons. 

Foods that contain the polysaccharide starch

Starch is one of the main sources of carbohydrates in the foods we eat. Starch is produced by most plants we consume along with some ferns, mosses, algae and protozoa. As we eat foods that contain starch, our bodies break down this polysaccharide into smaller components (monosaccharides) which the body then absorbs for a range of different uses. 

Starch is a major source of glucose in the human diet and acts as an energy source for our bodies. The rate at which this energy is absorbed depends on the type of food consumed, how it’s cooked or prepared and the addition of other food components. 

Foods that contain starch:-

  • Potatoes
  • Bread
  • Cereals and cereal products (breakfast bars, etc)
  • Rice
  • Grains (oats, barley, bulgur)
  • Pasta
  • Corn
  • Peas
  • Beans (lima, kidney, pinto, etc)
  • Lentils
  • Peas
  • Flour (wheat, millet, sorghum, etc)
  • Processed food (starch additives)

 

Glycogen is a polysaccharide 

When our bodies need a burst of energy it can draw this energy from its glycogen stores. Mainly stored in our liver and muscles, our bodies can quickly mobilise glycogen when needed to be used as a fuel source. 

The types of foods we eat along with our overall activity levels will all impact on glycogen storage levels in the body. Eating carbohydrate-containing foods allows glycogen formation. Low-carb or ketogenic diets for example, deplete glycogen levels in the body so the body will metabolise protein and fat for energy instead of glycogen. 

Foods that contain carbohydrates:- 

  • Fruits
  • Starchy vegetables
  • Grain foods such as bread, pasta
  • Beans
  • Quinoa
  • Brown rice
Foods that contain the polysaccharide cellulose

Cellulose is an important component in many plants as it is the main substance in the walls of plant cells which helps plants maintain structure. As part of our diet we consume cellulose as ditary fibre which helps to maintain our digestive tracts in good working order by keeping food moving through our gut, into our intestines and out of our body as waste as well as helping us to feel full.  

Foods high is cellulose (dietary fibre):-

  • Bran
  • Barley
  • Corn
  • Nuts
  • Fruit
  • Beans
  • Soy beans
  • Lentils
  • Beetroot
  • Flaxseed
  • Wholegrain breakfast cereals
Foods that contain the polysaccharide chitin

Chitin is the second most abundant polysaccharide found in nature directly after cellulose. Chitin is a major ingredient in the structural components of the exoskeletons of many crustaceans, crabs, shrimp and also plays an important role in the cell walls of fungi. 

Research suggests that consuming chitin can help lower blood cholesterol levels and certain chitin derivatives have been found to have antioxidant properties.  

Foods that contain chitin:-

  • Edible insects e.g. crickets
  • Mealworms
  • Insect powders
  • Soft shell crab
  • Prawn shells

 

References

https://journals.sagepub.com/doi/pdf/10.1177/1934578X1701200606

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6267054

https://www.diabetes.org/healthy-living/recipes-nutrition/understanding-carbs/types-carbohydrates

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4945249/

http://www.brooklyn.cuny.edu/bc/ahp/LAD/C4c/C4c_polysaccharides.html

https://pubmed.ncbi.nlm.nih.gov/2993399/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5094803/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2920538/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2920538/

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