Carbohydrates
Carbohydrates are sugars or polymers of sugars such as starch that can be hydrolyzed to simple sugars by the action of digestive enzymes or by heating with dilute acids. Carbohydrates are compounds which contain carbon, hydrogen and oxygen. Carbohydrates are a class of energy yielding substances which include starch, glucose, cane sugar, milk, sugar etc.
Classification
Class |
Components |
Comments |
Free sugars |
Mono and disaccharides |
Associated with high blood glucose and insulin, links with diabetes; coronary disease, cancer and the ageing process |
Insulin |
Sugar alcohols |
Sparingly absorbed
Partly metabolized |
Short-chain carbohydrates |
Oligosaccharides Insulin |
May be fermented in the large bowel. Innulin and fructooligosacchardies have been shown to stimulate growth of potentially beneficial bifido bacteria |
Polysacchardies |
|
|
Starch |
Rapidly digestible starch RDS, (Includes maltodextrins) |
RDS and RAG* associated with high blood glucose and insulin. Links with diabetes, coronary heart disease, cancer and the ageing process |
| Slowly digestible starch, SDS |
Only moderate influence on blood glucose and insulin Nutritionally the most desirable form of starch |
| Resistant Starch, RS. |
Desirability safety of increase in foods requires further evaluation |
Nonstarch Polysaccharides NSP |
Cell-wall NSP in unrefined plant foods, |
Encapsulate and thus slow are of digestion and absorption of sugars and starch |
Functions
-
Source of energy- Carbohydrates are least expensive source of energy to the body. Every gram of carbohydrate, sugar or starch, when oxidized yields on an average 4 kilo calories. Since Indians consume large quantity of cereals, most of the requirement of energy is met by carbohydrates.
-
Protein sparing action-The body uses carbohydrate as a source of energy, when they are adequately supplied in the diet, sparing protein for tissue building. If diet does not supply adequate calories, the dietary protein is oxidized as source of energy. There is also breakdown of tissue proteins to a greater extent. This function of carbohydrate of serving as a source of energy and preventing dietary protein from being oxidized is called protein sparing action.
- Oxidation of fats- In oxidation of fats the acetyl Co A formed from the oxidation of fatty acids reacts with oxaloacetic acid from carbohydrate and amino acid metabolism to form citric acid which is oxidized through the TCA cycle back to oxaloacetic acid through a series of reactions. Hence, for b-oxidation of fats, carbohydrate is essential. If adequate amount of carbohydrate is not consumed, intermediary products of fat oxidation are accumulated. Acetone, acetoacetic acid and b-hydroxy butyric acid accumulate and produce ketosis.
- Indspensability for nervous system -The main source of energy for central nervous system is glucose. Prolonged hypoglycaemia can lead to irreversible damage to the brain tissues.
- Role in muscle -Carbohydrates are the major source of energy for muscular work. During muscular contraction, glycogen is broken down to lactic acid through glycolysis. During the recovery period, lactic acid is first oxidized to pyruvic acid and then to acetyl CoA which is then oxidized to CO2 and H2O, thus producing energy for muscular work.
- Role in liver - These include detoxifying action and regulating influence of protein and fat metabolism. Liver is rich in glycogen and is more resistant to certain poisons such as carbon tetrachloride, alcohol, arsenic and toxins of bacteria. The rate of oxidation of amino acids in liver is diminished if abundant supply of carbohydrates is available.
- Source of energy for heart muscle -The heart muscle mainly uses glucose as source of energy. In hypoglycemia a definite adverse change in the working of the heart has been observed.
- Synthesis of ribose from glucose -The pentose ribose is present in RNA and in many nucleotides. It is formed in the body from glucose by Hexose Mono Phosphate pathway.
- Conversion to fat - Excess of calories fed in diet in the form of carbohydrate is stored as fat in the adipose tissue. When the body is in need to energy, it can be realized from the adipose tissue.
- Promotes growth of desirable bacteria - Lactose has several functions in the gastrointestinal tract. It promotes the growth of desirable bacteria, some of which are useful in the synthesis of B-complex vitamins. Lactose also enhances the absorption of calcium.
- Contribution of dietary fibre- Dietary fibre gives no nutrients to the body. It stimulates the peristaltic movement. It helps in preventing many degenerative diseases.
- Biosynthesis of amino acids -The carbon skeleton for the synthesis of alanine, aspartic acid and glutamic acid are provided by glucose during its oxidation, from pyruvic acid, oxalo acetic acid and a-ketoglutaric acid respectively
Dietary Fibre
Dietary Fiber includes a number of polysaccharides and lignin that are not digested by the enzymes of the gastrointestinal tract. These nonnutritive substances have specific chemical structures with varying physical and chemical properties their quantitative determination in foods.
Sources
The best source of carbohydrates are cereals like rice, wheat, millets, roots and tubers like potato, tapioca, sweet potato, yams, pulses, sugar, jaggery, honey, fruits, vegetables etc., Grain foods, roots and tubers are largely composed of starch, complex carbohydrate. Glucose derived from starch and other sugars present in the diet is the main source of energy in the body.
Foods contain non-digestible carbohydrates like cellulose, hemicellulose, gums, pectins and lignins. These indigestible carbohydrates are designated as dietary fibre or ‘unavailable carbohydrates’. These are not digested in the digestive tract and most of them are voided as such and thus contribute to the bulk of stools. Lack of adequate dietary fibre in diets containing refined foods, leads to constipation and colon cancer.
Carbohydrate content of foods
| Name of Food Stuff |
Carbohydrate g/100g |
| Sugar |
99 |
| Jaggery |
95 |
| Sago |
87 |
| Rice |
78 |
| Dates dried |
76 |
| Wheat flour, whole |
69 |
| Red gram dhal |
58 |
| Skimmed milk powder |
51 |
| Whole milk powder |
38 |
| Potato |
23 |
|
 |
Requirement
A minimum of 100g of carbohydrate are needed in the diet to ensure efficient oxidation of fats. Most diet supply more than this amount. As it is the cheapest source of food energy, it supplies up to 80 % of the calories in the low cost diets. If the proteins supply about 10% of the calories, fat 20% then carbohydrate must supply the remaining 70% calories. The daily diet of an adult should contain at least 40 g of dietary fibre.
Sources http://www.onlinegardenertips.com/images/What-Is-Potato-Plant-Pesticide.jpg
http://www.birnstihl.com/photos/product/Carbohydrate%20food%20shot%20@%20350.jpg
http://www.veeshunexim.com/Images/Products/Jaggery.jpg
http://img.alibaba.com/photo/11149679/Thai_Fruits_Mango_Guava_Baby_Banana_Pineapple_.jpg |
