Water is a molecule composed of two hydrogen atoms (H₂) and one oxygen atom (O), forming H₂O. It is essential for all forms of life and makes up an average of 60% of an adult's body weight. Water is a universal solvent, playing a central role in many biological reactions and the transport of nutrients.
In the human body, water is distributed into two main compartments:
Intracellular water (about 60% of total body water): Found inside cells, it is essential for their proper function.
Extracellular water (about 40% of total body water): Found in the blood, lymph, and interstitial spaces surrounding cells.
Water is essential for physiological balance and survival. A loss of just 1 to 2% of body weight in water can lead to decreased physical and cognitive performance, while a 10% loss can be life-threatening.
Water is essential for:
Water is primarily absorbed in the digestive tract, specifically in:
The stomach: A small amount of water is absorbed immediately.
The small intestine: Most water absorption occurs here, facilitated by osmotic gradients that allow water to pass into the bloodstream.
The colon: It recovers some of the unabsorbed water to limit losses and maintain hydration.
Once absorbed, water circulates in the blood and lymph and is then distributed to cells and tissues as needed.
Water balance is regulated by the kidneys, which adjust the amount of water excreted in the urine based on the body's needs. The antidiuretic hormone (ADH) plays a key role by increasing water reabsorption in the kidneys when the body is dehydrated.
Water plays several vital roles in the body:
Water allows for the circulation of essential nutrients (glucose, amino acids, electrolytes) in the blood.
It facilitates the elimination of metabolic waste through urine, sweat, and respiration.
When it is hot or during physical activity, water enables sweating, a key mechanism to release excess heat.
Present in synovial fluid, water protects joints and reduces friction.
Water is also a major component of cerebrospinal fluid, which protects the brain and spinal cord.
Many chemical reactions in the body require water, including hydrolysis (enzymatic reactions involved in digestion).
Water helps dissolve and transport electrolytes (sodium, potassium, chloride) essential for blood pH regulation and nerve conduction.
Water needs vary based on several physiological and environmental factors.
Adults: Around 2 to 2.5 liters per day (including water from food).
Children: Between 1 and 1.5 liters, depending on age and physical activity.
Athletes or people in hot climates: Due to greater water loss, intake may increase to 3 to 4 liters per day.
Muscle effort increases heat production and water loss through sweat, requiring higher hydration levels.
In hot climates, sweating is more intense, leading to higher water needs.
Water-rich foods (fruits, vegetables, soups) contribute to hydration.
A diet high in salt or protein increases renal load, requiring more water intake.
Fever, vomiting, and diarrhea cause rapid dehydration, necessitating increased water intake.
Certain kidney and heart diseases can affect water regulation, requiring specific adjustments.
Elderly individuals have a reduced sense of thirst, increasing the risk of dehydration.
Infants have higher water needs relative to their body weight.
Water is essential for the proper functioning of the human body. It ensures nutrient transport, temperature regulation, waste elimination, and electrolyte balance.
To maintain good hydration, it is crucial to drink regularly, adjusting intake based on physical activity, climate, and individual needs. Even mild dehydration can have negative health effects, highlighting the importance of conscious and adequate water consumption.
Throughout this course, we have explored the fundamental principles of modern nutrition, emphasizing the role of macronutrients, micronutrients, and water in maintaining health and well-being. Key takeaways include:
By applying these principles, individuals can make informed dietary choices to enhance overall health, performance, and longevity. A well-balanced, nutrient-rich diet, combined with hydration and an active lifestyle, forms the foundation of long-term well-being.
Let’s take this knowledge forward and make nutrition a cornerstone of a healthier life!
