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Polysaccharides are complex macromolecules essential for many bodily functions found in a wide variety of carbohydrate-based food sources. The four monosaccharides, often referred to as simple sugars, of fructose, glucose, lactose, and galactose, can join together to produce a polysaccharide. When glucose and fructose are joined together, they produce sucrose, or table sugar, one of several common disaccharides. Other types of polysaccharides include starch, glycogen, and xanthan gum in plants. Starches are known as storage polysaccharides because they contain glucose, which is the most easily broken down sugar for energy, and is concentrated in all grains, potatoes, beans, and more.
Glycogen is one of the main polysaccharides that is similar in structure to starches, and is considered the primary energy storage molecule in animals, as well as lower life forms, such as yeast and fungi. Glucose is a core component of the glycogen molecule, and it is released from glycogen through a process of hydrolysis, or chemical decomposition in water. When foods are said to have a glycemic index, it is this ability of a glycogen-based food molecule to release glucose into the bloodstream for energy. Foods with glucose as their primary form of sugar have the highest glycemic index, and these include processed wheat grains, dates, and white bread.
Foods such as bananas and potato chips can have a different glycemic index than their molecular structure would suggest. This is because certain factors slow down the breaking up of carbohydrates to release glucose. Sugars, such as fructose in bananas or lactose in dairy products, are more slowly digested than glucose-based foods. A food like potatoes with a high glycemic index that is processed into potato chips will also slow down digestion, as fat added to the chips inhibits the breakdown of glucose from the potato starch. Unprocessed starch and foods with a lot of fiber can be hard for the body to digest as well, so brown rice would be broken down more slowly than rice cereal, and raw beans slower than cooked beans.
Since polysaccharides themselves are insoluble in water, they can store glucose as an energy molecule without affecting the cells they are in until needed. This is why consuming large amounts of carbohydrates can contribute to weight gain. There is nothing essentially wrong with carbohydrates, but they are polysaccharide molecules designed as an efficient way to store energy in stable form for both plants and animals. Their ability to hold energy in the form of glycogen in animals and as cellulose in plants is the same as storing calories, and excess calorie consumption is the root cause of weight gain.