In healthy adults, fluid intake is regulated by thirst. Water is an essential nutrient for life and is considered the ideal drink to quench thirst and ensure hydration.
Ironically, it is very often ignored as part of our dietary recommendations. Most people are familiar with the general recommendation for adults of eight glasses of water per day.
Yet, estimating water or fluid intake requirements is not easy and individual requirements are highly variable.
The National Research Council (NRC) recommends a daily water intake of approximately 1ml/kcal energy expenditure. The eight glasses of water per day is based on this recommendation and on the average weight of a 70kg male.
No single formula fits every individual or every situation and water intake recommendations also depend on other factors such as activity, humidity, climate, body temperature and body composition.
Many choose alternatives
Despite the fact that water is considered as the ideal fluid to drink, many people choose alternatives and prefer other drinks such as cool drinks, fruit juices, coffee, tea, milk or sport drinks.
These beverages may or may not contribute to the daily energy intake of the individuals consuming them, depending on their composition.
For instance, a glass of ordinary sweetened carbonated cool drink provides at least 418 kJ and a glass of artificially sweetened cool drink less than 5 kJ, making the latter by far a better choice for an overweight, inactive adult.
The increase in the incidence of obesity and lifestyle diseases such as diabetes and heart disease certainly require of us to create awareness on the importance of better food and drink choices as one of the interventions which help attain and maintain a healthy body weight throughout our lives.
To make sound choices even more difficult, or rather interesting, is the fact that consumers are faced with a host of products and functional foods/drinks that offer anything from micronutrient-enriched water to “cancer-fighting teas”, such as green tea, to a host of other products offering “miraculous” health benefits.
With the plethora of such beverages, consumers may often not only need some guidance on sound choices to quench their thirst, but also on how to include such beverages as part of their daily varied diet.
The primary determinant of hydration and fluid intake in humans is thirst. Infants and the elderly, who are respectively known to be unable to communicate their thirst and have a blunted thirst sensation, should receive special attention in relation to daily fluid intake.
Water is part of every body cell comprising, on average, 50% of body weight in women and 60% in men. Every system and function in the body depends on water.
For example, water aids in the digestion of food, carries nutrients to cells and provides a moist environment for ear, nose and throat tissues.
The amount of fluid consumed per day is approximately equivalent to the amount lost. Mild dehydration affects a wide range of cardiovascular and thermo regulating processes and responses.
Dehydration of 3-5% of body weight decreases physical strength and performance, and is the primary cause of heat exhaustion. Daily turnover of water is approximately 4% of total body weight and even higher proportions in children.
Water losses from the lungs and skin (insensible losses; 500 - 1000ml/day) are responsible for approximately half of the daily turnover and sensible losses from stools (50 -100ml/day) and urine account for the rest of the daily losses.
Yet, despite of changes in body composition and function as well as the environment, most healthy people manage to regulate daily water balance well across their lifespan.
In February 2004, The Institute of Medicine (IOM) issued new recommendations regarding our fluid requirements. According to the new guidelines healthy adults may use thirst to determine their fluid needs. Exceptions to this rule include anyone with a medical condition requiring fluid control; athletes; and people taking part in prolonged physical activities or whose living conditions are extreme.
The IOM report did not specify requirements for water but made general fluid intake recommendations for healthy sedentary adults living in temperate climates:
- Men: 3.7 liters (15 glasses of 250ml) of water per day from all dietary sources
- Women: 2.7 liters (11 cups of 250ml) of water per day from all dietary sources
This may seem like a lot of fluid to take in per day, but remember that these guidelines are for total fluid intake from all food and beverages.
Approximately 80% of our water intake comes from drinking water and other beverages, and the other 20% comes from food. Assuming these percentages are accurate for most of us, the recommended amount of beverages, including water, would be approximately 9 glasses of 250ml for women and 12 cups of 250ml for men.