Water in food

WATER IN FOODS:

Water presents in foods in four ways-

1.     Free water: in which substances are dissolved or dispersed. Examples of this type are found in cytoplasm, intercellular fluid and many other circulating fluids of tissues.

2.    Water as hydrates: which is formed either when hydrogen bonds are established between water molecules and ions or molecules which contain oxygen or nitrogen or when unshared electrons of oxygen are coordinated with an ion. Starch, proteins and many other organic compounds important in foods as well as salts from hydrates.

3.    Imbibed water in gel: Imbibed water may not be different from water held as hydrate. Some substances picked up water and swell when they come in contact with water. They are said to be “imbibed” water. This may be accomplished by hydrogen bonding.

4.    Adsorption on the surface: this type of water is held when all the surfaces are exposed to air in which water vapor is present. Solids which are very finely divided have a very large surface area and consequently have a high adsorptive capacity.

                                       WATER AND NUTRITION

Water is the largest constituent of the body. About 60-70% of the total weight consisting of water. The water content of soft tissues ranges from 70-80% while that of bone about 20%.

Distribution of water in the body:

Total body weight	70kg	100(%of bodyweight)
Total water	50kg	70
1.     Intracellular 2.    Extracellular Ø  Plasma Ø  Lymph Ø  Tissue fluid	35kg             12kg              3kg              5kg              4kg	50               17                4                7                6
3.    Miscellaneous	3kg	4

                                            WATER INTAKE AND LOSS

Water is lost continuously from the body in the following ways:

1.     Via kidney as urine.

2.    Via skin in the form of insensible perspiration and as sweat.

3.    Via lung in the expired air.

4.    To a small extent via the large intestines in the faces.

5.    In the lactating women in the milk.

Water is taken in the food and also as drinking water. In addition, water is formed in the tissues by the oxidation of hydrogen present in fats, carbohydrates and proteins. Approximate quantitative data per day for an adult weighing 70kg, given in below:

Water intake and loss from the body:

Water intake	Temperate climate                               (ml)	Tropical climate (ml)
Drinking water	1500	2000-5000
In food	1000	1000-2000
By oxidation of CHO, protein and fat in the tissues	300	300
TOTAL	2800	3300-7300

Water loss	Temperate climate                               (ml)	Tropical climate (ml)
In urine	1500	1000-1500
Via skin	800	1800-5200
Via lungs	400	400
In faces	100	100-200
TOTAL	2800	3300-7300