Carbohydrates are so called because at the chemical level they contain carbon, with oxygen and hydrogen in the same proportion as in water. Carbohydrates are most important source of energy in our body. They are utilized as fuel by the human body and constitute the most vital source of energy for the nervous tissues. Our body stores any extra sugar in our liver and muscles for when it is needed. Carbohydrates are the cheapest source of energy for the vast majority of people in the tropics.
Carbon, Hydrogen and oxygen are formed into units known as saccharide groups. Carbohydrates are classified according to the number of saccharide groups present: monosaccharides have one, disaccharide have two , while starches and glycogen are examples of polysaccharides that have more than two saccharide groups linked together. A balanced diet should provide around 60-75% of total calories from carbohydrate. One gram of carbohydrates equals to 4 kcal.
- Monosaccharides – (Simple carbohydrate) Monosaccharides are the simplest form of carbohydrates. All carbohydrates are reduced to monosaccharide state before absorption and utilization. They contain three to six carbon atoms and are accordingly termed triose ,tetrose ,pentose oe hexose.
Glucose, Galactose and fructose arte important hexoses for human nutrition.
- Glucose- it is a white crystalline substance , with a sweet taste, freely soluble in water. Glucose is not a sweet as a household sugar, sucrose.
Relative sweetness of compounds in water(sucore=1)
|Less sweet than sucrose||Sweeter than sucrose|
- Fructose- Fructose is a important commercial sweetener , used particularly in soft drinks. It is present in honey, fruits and vegetables. For humans, the main source of fructose is sucrose (household sugar), which on breakdown releases equal amounts of glucose and fructose. The latter is absorbed by an active transport mechanism and converted to glucose, mainly by the liver cells. Fructose enters the cells without the aid of insulin and hence is sometimes recommended in Diabetes type 2.
- Galactose- Lactose (milk sugar) breaks down into glucose and galactose during digestion. It is not present in fruits and vegetables.
- Disaccharides –
- Sucrose- (cane sugar) is table or household sugar. In the intestine, sucrose is broken down into the monosaccharide fructose and glucose, which are absorbed. High sucrose intake tends to damage the liver and significantly elevates the enzymes alanine aminotransferase and aspartate aminotransferase.
- Maltose- Maltose is an intermidaite product formed in the process of conversion of starch into glucose.
- Trehalose- Trehalose is a dissacharide broken down to two molecules of glucose by the enzyme trehalase. It is nutritionally not so important.
- Polysaccharide-(complex carbohydrate) Polysaccharides are composed of manymmolecules of monosaccharides linked together. The important of polysaccharide in human nutrition are starch, glycogen, cellulose and fiber.
- Starch-starch is the storage form of carbohydrate. Starch is found in cereals,pulses,potatoes and sweet potatoes. Its granules are seen within the thin walled cells. Cooking helps in digestion of starch. Boiling causes swelling of the starch granules and rupture of the cell walls, allowing better digestion.
- Glycogen- glycogen is a complex molecule consisting of many glucose units.It is stored mainly in the liver and also in the muscles. The total glycogen reserve of the body is capable of supplying energy for just over half a day. In a normal person any amount utilized is replenished immediately.
- Cellulose- It is a long chain like molecule composed of many glucose units. It forms the cell walls of vegetable, fruits, and cereals. Human intestine cannot digest cellulose whereas cattle can digest and utilize cellulose. Constipated person can be helped by cellulose which provides an unabsorbable bulk, distends the intestine and stimulates peristalsis.
Difference between complex carbohydrate and simple carbohydrate