A Carbohydrates Overview
Dietary carbohydrates consist of simple carbohydrates, called sugars and complex carbohydrates such as starches and fibers. Complex carbohydrates are made from simple sugars but are complex because more than two sugars are bound to each other in a molecule.
Simple carbohydrates can be monosaccharides (single molecuels of sugars such as glucose) or disaccharides consisting of two sugars bound together. An example of a disaccharide is sucrose which consists of one molecule of glucose bound to one molecule of sucrose. There are three monosaccharides that are most important for human nutrition – glucose, fructose and galactose. Glucose (also known as dextrose) is the body’s preferred form of sugar. Glucose circulates in the blood and is known as blood sugar. Fructose is simlar to glucose but also very different. Fructose is much sweeter and is occurs naturally in fruits and honey. Fructose does not require insulin to enter cells, more on this later. Galactose is one of the two sugars that make up lactose, the sugar in milk.
Disaccharides must be broken down to be utilized by the body in a process called hydrolysis. Some impotant disaccharides include sucrose (made up of one molecule of glucose and one molecule of fructore) also known as table sugar, Lactose, or milk sugar is made up of one molecule of glucose bound to one molecule of galacatose. Maltose consists of two glucose molecule bound to each other and forms when starches are broken down.
Complex carbohydrates consist of many sugar molecules bound to one another. Three important complex carbohydrates include glycogen, starches and fiber. Glycogen is composed of many molecules of glucose and is the main carbohydrate storage in the animals and is stored in the liver and skeletal muscle.Starch is the main storage carbohydrates in plants. Non-starch carbohydrates form structural components of plants and are important sources of fiber.
Glycogen is found in only very small quantities in the diet but as the carbohydrate storage, it is very important. The highly branched nature of glycogen makes it readily available as an energy source when needed. Starch is also composed of glucose and is found in the diet in grains, such as rice and corn, potatoes and beans. Starches are a major source of energy in the diet.
Fiber, such as cellulose, are also composed of glucose but the glucose is bound in straight chains which are resistant to the digestive enzymes in humans. Their indigestible nature makes fiber very important for human health. Fiber provides “roughage” and bulk to fecal matter and helps to keep the digestive tract healthy.
Carbohydrates, other than fiber, are first broken down in the digestive tract and then absorbed into the blood stream where they can be utilized as energy or stored as fats. To be utilized, most sugars are first converted to glucose. The body secretes a peptide hormone called insulin that signals the cell to absorb glucose as well as amino acids into the cell. Without insulin, very little glucose can enter a cell. Fructose, as mentioned earlier, can be utilized by cells directly without the help of insulin.
Carbohydrates provide 4 calories per gram so if you consume 100 grams of carbohydrates, then you have taken in 400 calories. When carbohydrates are stored as glycogen, they draw water into the tissue. This is particularly useful since when glycogen is broken down, it releases water which can also be used by the cells.