Human Nutrition 3(3+0)

Lesson 45 : Water Functions and Water Balance

Water intake and loss

Loss of water from the body is continuous. The body loses water

1. via kidney as urine;
2. via the skin in the form of insensible perspiration and as sweat;
3. via the lungs in the expired air;
4. to a small extent via the large intestines in the faeces and
5. through milk during lactation. Water is taken in food and also as drinking water.

In addition, water is formed in the tissues by the oxidation of hydrogen released during fat, carbohydrate and protein metabolism.

• Water intake and source of body water: Water is taken as drinking water, about 1500 ml (in temperate climate), through food, 1000 ml; and from oxidation of carbohydrates, fats and proteins in tissues, 300 ml.

• Water loss: The body loses water through urine, about 1500 ml; via skin 800 ml; via lungs 400 ml and in faeces 100 ml. In a normal individual, the water intake is approximately equal to water lost from the body and thus the water balance of the body is maintained fairly constant.