Sunday, April 13, 2014

Therapeutic food polysaccharides

Polysaccharides are complex carbohydrates that are composed of many (poly) single glucose (saccharide) units. Polysaccharides constitute a wide variety of biological polymers with diverse composition, physical characteristics and biological activity. The important dietary polysaccharides include starch, glycogen and fibres. Starch is a storage polysaccharide of plants and the most important dietary carbohydrate worldwide. The primary function of starches and sugars is to supply energy to cells especially brain cells that depend on glucose.  One gram of carbohydrate provides 4 calories of energy. Body stores of carbohydrates (liver and muscle glycogen) are relatively small but still serve as an important energy reserve. If too much of sugar is in the body, it is converted into fat.The most important digestible polysaccharides include starch, glycogen and dextrin. Non-digestible polysaccharides such as cellulose provide important bulk to the diet and categorized as dietary fibre.  Cooking not only improves the flavour of starch but also makes digestion easier.
Digestion of starch is as follows: Starch + water-> soluble starch ->dextrins -> maltose -> glucose.
Some starch in foods escape digestion is called resistant starch, which can make up as much as 8% by weight of a food high in starch. The undigested starch that moves into the colon plays an important role in health. Complex carbohydrates are sub-categorized as starchy complex carbohydrates and fibrous complex carbohydrates.In short carbohydrates are called carbs or carbos.

Refined and unrefined carbohydrates

Refined carbohydrates are altered so that they are not only easy to digest but also provide high amounts of glucose entering the bloodstream rapidly. Whole grains and complex carbohydrates slow down the absorption of simple sugars from the diet.  Modern diets are over-processed foods with more refined carbohydrates with less or no fibrous material. Refined carbohydrates are essentially refined sugars and refined flours. Unrefined carbohydrates are the kind found in whole grains, beans, fruits and many vegetables. Generally refined carbohydrates are less healthy for our bodies and unrefined carbohydrates are healthier.

Starchy complex carbohydrates

Starch provides the major source of energy in the diet of man. It occurs in cereal grains, pulses, tubers, bulbs and fruits. Starches contain only glucose residues. Starch is a mixture of structurally distinct polysaccharides, called amylase and amylopectin. Cereal starches usually contain 25% amylase and 75% amylopectin. Whole grain cereals and wheat breads are good examples of slowly assimilated, energy-dense, unrefined starchy complex carbohydrates. White bread and white rice are examples of refined complex carbohydrates. A diet rich in starches and dietary fibres helps prevent heart disease, diabetes, GI disorders and possibly some types of cancers. The recommended dietary allowance (RDA) for carbohydrate is 130grams per day. The Dietary Reference Intake (DRI) committee advised the people to eat plenty of whole grains, vegetables, legumes and fruits – enough to provide  half (45-65%) of the daily energy  from carbohydrates. Sugars that occur naturally in fruits, vegetables and milk are acceptable. Excessive sugar intake may cause rapid elevations in blood sugar or contribute to obesity. On the other hand sustained hypoglycemic shock causes irreversible brain damage.

Fibrous complex carbohydrates

Dietary fibre(DF), also called roughage is indigestible because it cannot be broken down by digestive enzymes.Dietary fibre is a complex mixture of plant food components. Crude fiber(CF) is composed of cellulose, hemicellulose and lignin.The heterogeneity of dietary fibre is the primary reason for the diversity of its physiological effects. Dietary fibres are usually classified as soluble or insoluble based on their solubility. Plant foods contain both types of fibres in varying amounts, according to the plant’s characteristics. Insoluble fibres are gut –health fibres which are metabolically ferment in the large intestine and can be prebiotic. Chemically dietary fibres consist of non-starch polysaccharides (NPS) such as cellulose, resistant starch, resistant dextrin, inulin, lignin, waxes, chitin, pectins, beta-glucans and oligosaccharides. Insoluble fibres are found in whole grains, wheat bran, corn bran, legumes, nuts and seeds. Soluble fibres are found in oats, rye, barley, legumes (peas, soybeans, and beans), fruits (berries, plums, avocados, bananas) vegetables (broccoli, carrots, sweet potatoes, onions) and nuts (almonds).The DRI recommends 25 to 35 grams dietary fibres daily. The World Health Organization (WHO) recommends an upper limit of 40 grams of dietary fibres a day. Dietary fibres reduce the risk of colon cancer. Fibre –rich foods promote regular bowel movements, increase the size of faecal matter and lower cholesterol levels. Soluble fibres may lower cholesterol levels and can also lower blood sugar levels in hyperglycaemic people. Some researchers found that increasing fibre intake decreases the body’s need for insulin. The non-digestible fructo-oligosaccharides (FOS) fibres help keep the digestive tract healthy by nourishing and promoting friendly bacteria (Bifidobacteria, Lactobacilli).  ). These microbes use some of the "prebiotic fibres,” in the food as fuel for their own growth, and through their own metabolism produce molecules called short-chain fatty acids (SCFA). SCFA production by these microbes has been associated with a decrease in cancerous colonic cells, reduction of serum cholesterol, and maintenance of healthy blood sugar levels and healthy intestinal tract cell walls. Natural food sources of FOS include onions, garlic and asparagus. FOS helps to heal irritable bowel syndrome by exerting a regulatory action on bowel movement.
The dietary fibre hypothesis
It is postulated that dietary fiber (DF) is a protective factor against certain colonic disorders and certain metabolic diseases such as ischemic heart disease, diabetes mellitus and obesity (Burkitt et al., 1972,Trowell 1972).

Non-starch polysaccharides (NPS)

Chitin and Chitosan - Chitin is the most abundant amino polysaccharide composed of –beta-1,4-N-acetylglucosamine  monomers. Chitin is a fibre in shellfish shell such as shrimp, lobsters, crabs and krill. It is also found in common foods such as grain, yeast, bananas and mushrooms. The fibre of edible mushrooms is chitin.  There are three forms of chitin: α, β, and γ chitin. Chitosan is the most important derivative of chitin. Chitosan is a copolymer composed of N-acetyl-D-glucosamine and D-glucosamine units. Chitin contains 6–7% nitrogen and in its deacetylated form, chitosan contains 7–9.5% nitrogen. Intake of dietary chitin helps lower cholesterol, blood sugar and alleviates stomach and bowel ulcers, indigestion and constipation. Fibres help us clean our digestive tracts. The studies suggest that chitin and chitosan are excellent hypocholesterolemics that is they reduce total cholesterol. It is by the reduction in cholesterol that the biopolymers prevent heart disease and stroke. It is claimed that drinks containing chitosan help prevent tooth decay and other dental disease. It is suggested that consumption of chitosan at levels greater than 5% of the total diet might cause adverse effects.


Agar is a galactan polysaccharide that is derived from marine red algae and sea weeds. Agar yielding species (Agarophytes) are found in the families Gracilariaceae, Gelidiaceae, Phyllophoraceae and Germiaceae. Agar is used as a gelling agent in host of food and industrial applications. Agar contains calcium, iodine, phosphorus and iron. Agar has no calories, sugars, fats or carbohydrates. It is composed of 80% fibre. Agar prevents the body from storing unnecessary fats and sugars. Agar has shown to absorb bile, which may help lower the amount of cholesterol absorbed by the body. Agar is also used to treat diabetes and constipation.


Alginate is a algal polysaccharide (polyuronic) that is derived from marine brown algae. The gel of the brown algae contains sodium, calcium, magnesium, strontium and barium ions. Generally algal phycocolloids (i.e.alginate, carrageenan and agar) have been used as thickeners and stabilizing or emulsifying agents. Alginates provide viscous soluble dietary fibres, which help lower the rate of small intestinal absorption of glucose / cholesterol thereby reducing the onset of diabetes and/ or obesity. Alginates may reduce the activity of certain digestive enzymes in the upper GI tract. 

Health benefits

Complex carbohydrates are low glycemic and good carbohydrates. Eating complex carbohydrates provides vitamins, minerals and fibre. Complex carbohydrates are healthy. Complex carbohydrates are referred to as ‘slow burn carbohydrates’.
They provide the following health benefits:
1. Stabilize blood sugar levels
2. Promote weight loss
3. Improve memory
4. Aid in digestion
5. Prevent digestive discomforts such as constipation, bloating and gas.
6. Decrease the risk heart disease
7. Reduce blood cholesterol levels

Closing thoughts

        Intake of dietary fibers is generally accepted as being beneficial to both cardiovascular and colonic health. The National Cancer Institute recommended a fiber intake of 20 to 30 grams daily. The American Diabetes Association recommended eating 40 grams of fiber daily. Soluble fiber has greater cholesterol-lowering effect, while insoluble fiber is good for improving bowel function. Both types of fibers help regulate blood sugar and are important for general health.

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