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Principles of Human Nutrition


Regulation of water balance

Water concentration in human body

  • Water Is an essential nutrient more important than any other.
  • It constitutes 60 percent of adult body weight.
  • The percentage of water is propotional to the proportion of lean tissue.

Role of water in human body

  • Maintains blood volume.
  • Carry nutrients and waste products through out the body.
  • Participates in metabolic reactions.
  • Aids in regulation of normal body temperature.
  • Maintains the structure of large molecules such as glycogens and proteins.
  • Serve as a solvent for vitamins, minerals etc.
  • Why there is a need to maintain a water balance?
  • The human body uses and looses water every day.
  • There is a need to maintain a correct water balance for good health.
  • Maintenance of water balance is called osmoregulation.
  • In limited supply of water, conservation of water is a principle function of body.
  • In excess of water ,loss of water is an important function which is done by urination, sweating etc.

Water balance regulation

Following terms should be understand.

  • Water balance
  • Homeostasis
  • Intracellular fluid
  • Extracellular fluid
  • Interestitial fluid
Water balance

Water input=water output



  • The entire system of cell and fluids remain in delicate, but controlled is called homeostasis.
  • Intracellular fluid and extracellular fluid
  • Every cell contain fluid of exact composition that is best for that cell.


Intracellular fluid

Fluid inside a cell is called intracellular fluid.

Extracellular fluid

Fluid outside the cell is called extracellular fluid.

Interstitial fluid

The extracellular fluid that surround each cells is called Interstitial fluid.

Water losses

On average, looses of water is 2.5 liters daily.

The body must excrete minimum of 500 ml of water each day as urine enough to carry away the waste products generated by metabolic activities.

Above this amount excretion adjusts to balance intake.If a person drinks more water kidney excretes more urine and urine becomes more diluted.In addition to urine water is lost from lungs as vapour  and from skin as sweat; some is also lost in faeces.

Role of hormones in maintaining the water balance

  • ADH
ADH (anti diuretic hormone)

Thirst activates when water intake is inadequate, it is regulated by mouth , hypothalamus  and nerves.

In this situation blood become concentrated and then hypothalamus signals the pitutary gland to release anti diuretic hormone. ADH is a water conserving hormone it stimulates kidney to reabsorb water.If we need more water to excrete than release of ADH is inhibited.It is poduce in response to dehydration from pitutary gland of kidney to reabsorb water and therefore excrete less.

  • Therefore, stimulates kidney to reabsorb water.
  • ADH activity is retard by alcohol thus promote fluid loss and dehydration.
  • In addition to its anti diureticeffect. ADH elevates blood pressure and so called vassopressin 



Cells in kidney responds to low blood pressure by releasing an enzyme called renin.Through a complex series of events renin causes the kidney to reabsorb sodium.

Sodium reabsorption, in turns, always accompanied by water retention, which helps to restore  blood volume and blood pressure.

Therefore it initiates the pathway to that leads the production of angiotensin.


In addition to its role in sodium retention, renin hydrolayse a protein from liver called angiotensinogen to angiotensin

1. Angiotensin 1 is an inactive untillan other enzyme converts it into its active form ANGIOTENSIN

2.Angiotensin 2 is a power full vasoconstrictor that narrow the diameter of blood vessel, thereby raising a blood pressure. Angiotensin 2 constrict blood vessel thus stimulate the production of ADH and ALDOSTERONE.


In addition to acting as a vaso constrictor, angiotensin2 stimulate the release of hormones aldosterone from the adrenal glands.

Aldosterone signals the kidney to excrete potassium and to retains more sodium, and therefore water, because when sodium moves, water follows.

Again the affect is that water is need ,less is excrete.

Therefore, it regulates the sodium and potassium level


  • It is rare , but can occur with an excessive water intake and kidney disorders that reduce urine production
  • Excessive water ingestion (10 to 20) liters within a few hours dilute sodium concentration of blood and contributes to a dangerous condition called
  • So, we should follow dietary guidelines


What is Water?

It is transparent, odorless , tasteless liquid ,a compound of hydrogen and oxygen, H2O freeze at 32 degree Fahrenheit or 0 oC and boils at 212 degree Foor 100 degreeoC, that in a more or less impure state constitute rain, ocean, lakes, rivers etc. It contain 11.188 % hydrogen and 88.812% oxygen, by weight.

Hardness of Water:

Carbonates and bicarbonates of calcium and magnesium cause hardness. Water with more than 100 mg per liter hardness (expressed as calcium carbonate) called hard water.

Softness of Water:

Water with less than 50 mg   per liter hardness is called soft water.

Important Aspects of Water:

There are two aspects:

  1. Microbiological Aspect:

Quality of water is determine by examining the total number of organisms and specifically Coliform bacteria.

  1. Chemical Aspect:

Chemically water should be free of heavy metals, fluorides or dissolve toxic substances. Water is a Great transporter:

  • Besides being useful commodity, it is a transporter of numerous diseases. It leads to water borne diseases.

Water Borne Diseases:

Waterborne diseases are caused by drinking contaminated or dirty water. Contaminated water can cause many types of diarrheal diseases, including Cholera, and other serious illnesses such as Guinea worm disease, Typhoid, and Dysentery. Water related diseases cause 3.4 million deaths each year e.g bacillary dysentery, gastroenteritis and Diarrhea etc.

Diarrheal Disease:

Diarrhea is defined as the passage of three or more loose or liquid stools per day. Diarrhea is usually a symptom of an infection in intestinal tract which can be caused by a variety of bacterial, viral and parasitic organisms. Infection is   spread through contaminated drinking water, or from person to person of poor hygiene.


Key measure to prevent diarrhea include:

  • Access to safe drinking water
  • Improve Sanitation
  • Exclusive breastfeeding for six month of life
  • Good personal and food and hygiene.

Amoebic and bacillary dysentery are both infection of intestine that caus diarrhea.


It prevents through provision of safe drinking water.

International Standards for Safe Drinking Water:

Water for human consumption must be free from organisms and chemical.

ANS – 2016 (American National Standard) for Drinking water system component.

 Water Content of the Human Body:

Total body water

Water represents on average 60% of the body weight in adult men, and 50-55% in women. This means that, for a man of average weight (70 kg), body water content is about 42 liters. This average value varies among individuals, primarily because of differences in body composition: while the water content in lean body mass is constant among in mammals, at 73%, adipose tissue (body fat) is only about 10% water. Therefore, body fat relative mass directly influences total body water. This explains the influence of age, gender and aerobic fitness on total body water: women and older persons have lower total body water, because of lower fat-free mass. In contrast, athletes have relatively high total body water.

Factors Affecting intake of Water:-


The higher the consumption of water-rich foods (e.g., fruits, vegetables or soup), the higher the intake of water from food. Fruits and vegetables are indeed the food group which contains the most water: from 96% in a cucumber to 72% in an avocado, most contain more than 85% water.

Age :

The water requirement of a person increases with age.


The need for water during hot season is much higher than cold weather. A minimum of 900 ml water is required in temperate climate to balance water needed by the kidneys for elimination of waste products in urine. Sedentary man in a temperate environment requires about 2 L water per day. Much more is needed in tropical climate depending upon temperature, relative humidity and activity.

Activity (Exercise or physical activity):

When we exercise, our muscles produce heat that needs to be evacuated to maintain body temperature therefore, sweat is produced and that water loss should be balanced with adequate water intake, Water acts as a carrier of heat through blood, and as a refrigerant by removing excess heat via sweat evaporation on the skin.

Dietary Intake:-

Water is consumed as drinking water, beverages, and food moisture. But drinking water and beverages represent the majority of the total fluid intake, on average 70-80%, while water in food represents only 20-30%.

USDA Recommendation:

People need from under one liter a day to nearly four liters a day depending on their age, gender and health status. One liter equals 4.23 cups. Newborns and infants need 0.7 to 0.8 liters of water a day from breast milk or formula. Toddlers need 1.3 liters and young children up to eight years need 1.7 liters daily. Boys, ages nine to 13 need 2.4 liters daily. Teenage boys and adult men need 2.7 liters. Girls, ages nine to 13 need 2.1 liters and teenage girls need 2.3 liters. Adult women need at least 2.7 liters of water each day. Women need at least 3 liters of water during pregnancy and 3.8 liters daily for lactation.

Recommendations by life stage and gender:





Benefits of Meeting the Dietary Requirements:

  • Drinking water immediately after waking up replenishes water lost during sleep and flushes out the toxins accumulated during the night
  • Drinking plenty of water prevents formation of kidney stone.
  • It also helps treat urinary tract infection since drinking more water enables one to urinate more and flush out bacteria from the bladder
  • Water keeps one to remain alert and energetics. If dehydrated the blood is literally thick that makes it harder to circulate. As a result, the brain becomes less active and one feels confused and fatigued
  • Water prevents dehydration in patients suffering from diarrhea
  • Water prevents constipation and its complications. Too little water can hardens the stool and may lead to hemorrhoids and diverticulitis .drinking water and eating vegetables softens the stool.
  • Water helps reduce fever since the body temperature lowered during urination.
  • Drinking a glasss of water or two before meals helps reduce weight by actually reducing the amount of food taken to feel full.
  • Sipping water throughout the day is preferable rather than drinking two glasses all at once.

Water content in foods:

You get some of the water in your body through the foods you eat. Some of the water is made during the process of metabolism. You also get water through liquid foods and beverages, such as soup, milk, tea, coffee, soda, drinking water, and juices.

Natural, whole foods have the highest water content. Fruit and vegetables contain 80 to 98 percent water. Eating dense vegetables such as cucumbers, tomatoes, jicama, beets, carrots or celery with a meal or snack is one of the easiest ways to improve your hydration.

Foods with high water content:



Foods With Low Water Content:



  • Awan, J.A. (2017). Elements of Food & Nutrition
  • www.nrv.gov.pk
  • www.nap.edu
  • https://www.dictionary.com/browse/water


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