Polysaccharides are polymeric carbohydrate molecules composed of long chains of monosaccharide units bound together by glycosidic linkages and on hydrolysis give the constituent monosaccharides or oligosaccharides. They range in structure from linear to highly-branched. Examples include storage polysaccharides such as starch and glycogen, and structural polysaccharides such as cellulose and chitin.
As a rule of thumb, polysaccharides contain more than ten monosaccharide units, whereas oligosaccharides contain three to ten monosaccharide units; but the precise cutoff varies somewhat according to convention. Polysaccharides are an important class of biological polymers. Their function in living organisms is usually either structure or storage related. Starch (a polymer of glucose) is used as a storage polysaccharide in plants, being found in the form of both amylose and the branched amylopectin. In animals, the structurally similar glucose polymer is the more densely branched glycogen, sometimes called "animal starch". Glycogen's properties allow it to be metabolized more quickly, which suits the active lives of animals including humans.
Starch is a glucose polymer in which glucopyranose units are bonded by alpha-linkages. It is made up of a mixture of amylose (15–20%) and amylopectin (80–85%). Amylose consists of a linear chain of several hundred glucose molecules and Amylopectin is a branched molecule made of several thousand glucose units (every chain of 24–30 glucose units is one unit of Amylopectin). Starches are insoluble in water. They can be digested by breaking the alpha-linkages (glycosidic bonds). Both humans and animals have amylases, so they can digest starches. Potato, rice, wheat, and maize are major sources of starch in the human diet. The formations of starches are the ways that plants store glucose.
Glycogen serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue. Glycogen is made primarily by the liver and the muscles, but can also be made by glycogenesis within the brain and stomach.
Glycogen is analogous to starch, a glucose polymer in plants, and is sometimes referred to as animal starch, having a similar structure to amylopectin but more extensively branched and compact than starch. Glycogen is a polymer of α (1→4) glycosidic bonds linked, with α (1→6)-linked branches. Glycogen is found in the form of granules in the cytosol/cytoplasm in many cell types, and plays an important role in the glucose cycle. Glycogen forms an energy reserve that can be quickly mobilized to meet a sudden need for glucose, but one that is less compact and more immediately available as an energy reserve than triglycerides (lipids).
In the liver hepatocytes, glycogen can compose up to eight percent (100–120 g in an adult) of the fresh weight soon after a meal. Only the glycogen stored in the liver can be made accessible to other organs. In the muscles, glycogen is found in a low concentration of one to two percent of the muscle mass. The amount of glycogen stored in the body—especially within the muscles, liver, and red blood cells varies with physical activity, basal metabolic rate, and eating habits such as intermittent fasting. Small amounts of glycogen are found in the kidneys, and even smaller amounts in certain glial cells in the brain and white blood cells. The uterus also stores glycogen during pregnancy, to nourish the embryo.
Glycogen is composed of a branched chain of glucose residues. It is stored in liver and muscles.
• It is an energy reserve for animals.
• It is the chief form of carbohydrate stored in animal body.
• It is insoluble in water. It turns brown-red when mixed with iodine.
• It also yields glucose on hydrolysis.
Arabinoxylans are found in both the primary and secondary cell walls of plants and are the copolymers of two sugars: arabinose and xylose.
The structural component of plants are formed primarily from cellulose. Cellulose is a polymer made with repeated glucose units bonded together by beta-linkages. Humans and many animals lack an enzyme to break the beta-linkages, so they do not digest cellulose. Although humans can't digest cellulose, they do use it as dietary fiber. Cellulose is insoluble in water. It does not change color when mixed with iodine. If hydrolyzed, it yields glucose. It is the most abundant carbohydrate in nature.
Chitin is one of many naturally occurring polymers. Chemically, chitin is closely related to chitosan (a more water-soluble derivative of chitin). It is also closely related to cellulose in that it is a long unbranched chain of glucose derivatives. Both materials contribute structure and strength, protecting the organism.
Pectins are a family of complex polysaccharides that contain 1,4-linked α-D-galactosyl uronic acid residues. They are present in most primary cell walls and in the non-woody parts of terrestrial plants.
Polysaccharides generally perform one of two functions; energy storage or structural support. Starch and glycogen are highly compact polymers that are used for energy storage. Cellulose and chitin are linear polymers that are used for structural support in plants and animals (humans included) respectively.
Nutrition polysaccharides like starch and glycogen are common sources of energy. Many organisms can easily break down these types of polysaccharides to yield energy. Most organisms however, cannot metabolize cellulose or other polysaccharides like chitin and arabinoxylans. These carbohydrate types can be metabolized by some bacteria and protists but not by humans.
Even though these complex polysaccharides like cellulose and chitin are not very digestible, they provide important dietary elements for humans. Called dietary fiber, these carbohydrates enhance digestion among other benefits. The main action of dietary fiber is to change the nature of the contents of the gastrointestinal tract, and to change how other nutrients and chemicals are absorbed. Soluble fiber binds to bile acids in the small intestine, making them less likely to enter the body; this in turn lowers cholesterol levels in the blood. Soluble fiber also attenuates the absorption of sugar, reduces sugar response after eating, normalizes blood lipid levels and, once fermented in the colon, produces short-chain fatty acids as byproducts with wide-ranging physiological activities (discussion below). Although insoluble fiber is associated with reduced diabetes risk, the mechanism by which this occurs is unknown.
Although not yet formally proposed as an essential macronutrient, dietary fiber is nevertheless regarded as important for the diet, with regulatory authorities in many developed countries recommending increases in fiber intake.
An energy source from glucose units that are widely obtained from plants. Many starches are cereal grains, bread, pasta, pastries, cookies, potatoes, tapioca, wheat, oats, rye, barely, rice and yams to name a few. They are a polysaccharide energy source when digested in the body.
A structural polysaccharide in plants that when consumed, it acts as a dietary fiber. Cellulose is the most abundant organic molecule on earth, since it is the main component of plant cell walls. It can therefore be sourced from any plant based foods.
It acts more like a long-term storage option. Glycogen is mainly produced by the liver and muscles, but it can also be made during a process called glycogenesis, which occurs in both the brain and stomach. A small amount of glycogen is in shellfish and animal liver.
None of the polysaccharides are nutrients essential in a diet, you do not need to consume them in order to be healthy.
None of the polysaccharides are nutrients essential in a diet, you do not need to consume them in order to be healthy. However, when consumed, they can have added health benefits.
Digestible polysaccharides, such as starch, are digested (broken down) in the mouth and small intestine in several steps that eventually yield glucose, which is absorbed and used for energy. In other words, they are a source of energy; they provide about 4 Calories per gram. They also provide carbon atoms for the synthesis of fats, proteins and other substances in your body.
Non-digestible polysaccharides or dietary fiber, such as cellulose, promote the passage of food through the gut and thus help maintain bowel regularity.
Though the symptoms of a fiber-poor diet aren't always clear-cut, there are four key warning signs to watch for:
Constipation: If you're having fewer than three bowel movements a week, and the stools are hard and dry, you're constipated. Constipation can result from lack of fiber, but also from too little exercise and certain medications and supplements.
• Weight Gain: Fiber contributes to a feeling of fullness after a meal. If you're not experiencing that feeling, you may eat more than your body needs.
• Blood Sugar Fluctuations: If you have diabetes and find controlling your blood sugar difficult, talk to your doctor: you may not be getting enough fiber.
• Diet-Related Nausea Tiredness: Getting most of your calories from a high-protein/low-carbohydrate diet -- one rich in meat, eggs, and cheese and low in produce -- may lead not only to a rise in cholesterol, but also leave you nauseous, tired, and weak.
If intake is suddenly increased, you might notice some digestive issues.
If you are trying to diet, eating more fiber may be a good way to feel fuller without increasing your calorie intake.
Polysaccharides can be good for blood sugar control, but if you suddenly increase your intake, you might notice some digestive issues. Healthy sources of polysaccharides typically come packed with dietary fiber, an indigestible carb that helps control blood sugar and helps you feel satisfied after a meal. Fiber also plays a key role in digestion because it loosens and softens your stool, which prevents constipation.
But you know what they say -- too much of a good thing isn't always so good. If you quickly and significantly boost your fiber intake, you risk having your stool become too soft, which can lead to diarrhea. Suddenly upping your fiber intake can also contribute to bloating and flatulence. And, ironically, getting tons of fiber without also drinking enough water can dry out your stool, causing constipation.
That doesn't mean you should avoid fiber-rich carbs. If you've been eating a relatively low-fiber diet, incorporate fiber-rich foods into your diet slowly to give your system time to adapt, and drink at least 64 ounces of water daily to avoid constipation. Add 5 grams to your daily diet, then increase the amount by an additional 5 grams every two weeks, until you reach the recommended 25 to 35 grams of fiber daily, recommends the University of Michigan Health System.
If you are trying to diet, eating more fiber may be a good way to feel fuller without increasing your calorie intake. However, the same does not apply to eating more starch. In fact, the health effects of eating too much starch are somewhat similar to the health effects of eating too much sugar.
• Higher Blood Sugar – Contrary to popular belief, sugar is not the only food that can raise your blood sugar. Too much starch has similar effects. This is because starch is made up of a long glucose molecule that your body breaks down into simpler sugar as part of digestion.
• Gaining Weight – When you eat too much of anything, you can gain weight. The same is true for eating too much starch. There are actually about 3-5 calories for every gram of starch in a food. This can add up, especially with super starchy foods like potatoes. Like with sugar, your body converts any extra starch into fat in order to save the energy for later use. This means if you don’t burn those calories down the road, you can expect to gain weight.
This is just a brief overview of the effects that consuming too much starch can have on your body. It by no means signifies that starch is downright bad for you and you should never ever eat it. Just be careful not to consume too much of it and for all intents and purposes you can view starch in much the same way as you currently view sugar. If you are interested in losing weight and getting fit.
How much food -- and how many carbs -- you need daily depends on a few factors, including your age, metabolism and activity level. Generally, you'll want to get between 45 and 65 percent of your calories from carbohydrates -- that translates to 203 to 293 grams of carbs daily in a 1,800-calorie diet. If you're eating significantly more than that, you might miss out on essential protein and fat, which help maintain lean muscle and aid in nutrient absorption, respectively. Talk to a registered dietitian if you're struggling to follow a balanced diet -- a dietitian can recommend a target carb intake personalized to your health and lifestyle, as well as supply a personalized meal plan to help you reach your goals.