Carbohydrates

Carbohydrates

The 3rd major component of food is carbohydrate, which is the main source of energy, providing 4 kcals per gram. Carbohydrates is also essential for the oxidation of fats & for the synthesis of certain non-essential amino-acids.

Sources-

1.   Starch

2.   Sugars

3.   Cellulose

1.   Starch- basic to the human diet. It is found in abundance in cereals, roots & tubers.

2.   Sugars- comprise monosaccharides(glucose, fructose, galactose) & diasaccharides(sucrose, lactose, maltose).

·       These free sugars are highly water soluble & easily assimilated.

·       Free sugars along with starches constitute a key source of energy.

3.    Cellulose- which is the indigestible component of carbohydrate with scarcely any nutritive value, contributes to dietary fibre.

Carbohydrate reserve of a human adult-

Is 500 g. This reserve is rapidly exhausted when a man is fasting. If the dietary carbohydrates do not meet the energy needs of the body, protein & glycerol from dietary & endogenous sources are used by the body to maintain glucose homeostasis.

Dietary fibre-

Is mainly non-starch polysaccharide is a physiologically important component of the diet.

·       Found in- vegetables, fruits & grains.

·       It may be divided broadly into cellulose & non-cellulose polysaccharides which include hemi cellulose pectin, storage polysaccharides like inulin & the plant gums & mucilages. These are all degraded to a greater extent by the microflora in the human colon.

·       Two types of dietary fibre-

1.   Insoluble fibres- include cellulose, hemi-cellulose &   lignin

2.   Soluble fibres- pectins, gums & mucilages.

·       Functions of fibres-

1.   It absorbs water & this increases the bulk of the stool & helps reduce the tendency to constipation by encouraging bowel movements.

2.   Dietary fibres are resistant to digestion in the digestive tract. In large intestine the bacterial action causes emulsification of the fibre, thus making the stool soft & passage easier.

3.   By reducing the intestinal transit time of food it drastically reduces the possibility of putrefaction & formation of gases & toxic substances.

4.   Fibre also inhibits faecal mutagen synthesis by changing colonic pH & bacterial metabolism.

5.   Cancer of stomach & colon have been linked directly to a low fibre diet.

6.   Dietary fibre is known to be associated with reduced incidence of coronary heart disease.

7.   The fibre, particularly the gum & pectin, when ingested with a diet, are reported to reduce post-prandial glucose level in blood.

8.   People who eat well-balanced diet obtain enough roughage.

·       Fibre have no metabolic effects. However, too much of fibre can decrease the absorption of valuable micronutrients.

·       A daily intake of about 40 grams of dietary fibre is desirable.