Water would be considered the most important nutrient of all. Naturally so, considering the average adult male has 60% water content and about 51% in females. Males have higher water content than males due to their greater muscle mass, which stores water.
Water is vital for many physiological and biochemical processes within the body.
Drinking fluids contribute to about 60% of the daily water requirement. 30% comes from the consumption of solids and 10% is the result of oxidative processes in cells.
Water needs to be constantly replenished through the diet as we lose approximately 2.5litres of water daily. Water is lost through the urine and faeces, perspiration from the skin and evaporation from the lungs. When
fluid loss is equal to the fluid consumed, it is considered a state of water balance.
Most Westerners do not consume the daily recommendation of 6-8 glasses (2 litres) of water. We can cope with mild losses of water, but extreme losses of water and low intake can lead to dehydration. Chronic dehydration can be lethal.
Location of water in the tissues of adult males
| g/kg body weight | % total body weight | |
| Blood plasma | 41 | 7 |
| Interstitial lymph | 121 | 20 |
| Dense connective tissue and cartilage | 41 | 7 Bone Water417Transcellular water152.5Intraluminal gut water8.41.4Total extracellular water26043Total intracellular water34047Total body water600100 |
Source:Wahlqvist, Food and Nutrition, p.256
Hourly water loss at rest and during exercise of a 70kg individual
| Water lost at rest ml per hour | Water lost at rest % total | Water lost during exercise ml per hour | Water lost during exercise % total | |
| Skin | 15 | 16 | 15 | 1 |
| Lungs | 15 | 16 | 100 | 7 |
| Urine | 58 | 63 | 10 | 1 |
| Perspiration | 4 | 4 | 1200 | 91 |
| Total | 92 | 100 | 1325 | 100 |
Wahlqvist, Food and Nutrition, p.258
Daily output of electrolytes in perspiration and urine for an average adult person at rest
| Fluid | 24 hour volume | Na+ (mg excreted in 24 hours) | Cl- (mg excreted in 24 hours) | K+ (mg excreted in 24 hours) |
| Perspiration | 100ml | 115 | 144 | 20 |
| Urine | 1400ml | 3500 | 5400 | 2700 |
Wahlqvist, Food and Nutrition, p.258
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