Wholesome Dietetics and MNT

WATER ( H₂O ) / FLUID

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The volume, composition, and distribution of body fluids have profound effects on cellular function and activities. Meanwhile, the term dehydration means excessive loss of water; it can also be taken as the depletion of water in the body, irrespective of the cause. Causes of dehydration may be physiological, biochemical, environmental, etc.

Water is second to only oxygen when it comes to it’s vital importance to the body. One can live for a long time without food, but definitely not water.

OUR BODY WATER

Water is the largest single component of the body. At birth, water accounts for approximately 75% to 85% of total body weight; this proportion decreases with age and level of adiposity. Water accounts for 60% to 70% of total body weight in the lean adult and 45% to 55% of total body weight in the obese adult. Metabolically active cells of the muscle and viscera have the highest concentration of water, whereas calcified tissue cells have the lowest. Total body water is higher in athletes than in non-athletes and decreases significantly with age because of diminished muscle mass. Although the proportion of body weight accounted for by water varies with age and body fat, there is little day-to-day variation in the percentage of body water.

BIOCHEMICAL FUNCTION

Water is an essential component of all body tissues as it makes many solutes available for cell function and is the medium needed for all reactions. Water is essential for the physiologic processes of digestion, absorption, and excretion. It plays a key role in the structure and function of the circulatory system and acts as a transport medium for nutrients and all body substances (blood, lymph, proteins, hormones, enzymes& co-factors etc). Water maintains the physical and chemical constancy of intracellular and extracellular fluids and has a direct role in maintaining body temperature. Evaporation of perspiration cools the body during warm weather, preventing or delaying hyperthermia. Loss of 20% of body water (dehydration) may cause death, while loss of only 10% causes severe disorders. In moderate weather, healthy adults can live up to 10 days without water, and children can live up to 5 days(but not advisable at all !). In contrast, it is possible to survive for several weeks without food.

Distribution

Intracellular water (ICW) is the water contained within cells and accounts for two thirds of total body water. Extracellular water is commonly estimated to account for one third of total body water or 20% of body weight, and includes the water in plasma, lymph, spinal fluid, and secretions. Extracellular fluid is the water with dissolved substances in the plasma, lyrnph, spinal fluid, and secretions, and also includes

the intercellular (interstitial) water between and around the cells. Most interstitial water is part of intracellular fluid and is held in a gel in the intercellular spaces and is continuous with the plasma through pores in the capillaries. Abnormal accumulation of fluid in the intercellular tissue spaces or body cavities is called edema. The distribution of body water varies under different circumstances, but the total amount in the body remains relatively constant. The understanding of the role of body water in health and disease has improved through the use of bio-electrical impedance analysis (BIA), a measurement of electrical conduction used to estimate the amount of body water.

Balance

Shifts in water balance can have adverse consequences. For this reason, homeostatic regulation by the gastrointestinal(GI) tract, kidneys, and brain keeps body water content fairly constant, under normal condition. The amount of water taken in daily is approximately equivalent to the amount lost, thus, the need for constant hydration( fluid intake).

Water Intake

In healthy individuals water intake is controlled primarily by thirst. Both cellular dehydration and decreased extracellular fluid volume play a role in stimulating thirst. Changes in cellular water content are sensed by baroreceptors in the central nervous system that provide feedback to the hypothalamus, which is close to the centers that regulate antidiuretic hormone (ADH), also known as vasopressin. ADH signals the kidneys to conserve water. Baroreceptors in the vascular system are stimulated by decreased extracellular fluid volume (Kenney, 2001). These sensors stimulate the renin-angiotensin system. Renin is an enzyme that is released by the kidneys and acts as a catalyst in the production of angiotensin II, and one of the actions of angiotensin II is stimulation of thirst centers. The sensation of thirst is a signal to consume fluids(and must not be neglected). Water is ingested as fluid and part of food. The oxidation of foods in the body also produces metabolic water as an end product (remember Kreb’s cycle right?). The oxidation of 100 g of fat, carbohydrate, or protein yields 107g, 55g, or 4lg of water respectively, for a total of approximately 200 to 300 ml/day.

Again, approximately 200 litres of water are filtered by the kidneys each day. Another 10 litres enter the intestinal lumen. But under normal body function, about 99% of the water is reabsorbed. Consequently, the daily water loss amounts to 1.5L to 2L in the urine, and about 100ml in faeces. Some researches has it that about 1Litre of water is lost daily via perspiration(sweat) and expired air. Quantity of water loss by expiration is dependent on respiratory rate(RR), clinicians take note. Without speaking much grammar, what this is pointing at is that your daily water intake must be 1.5L or 2L (or more if you are resident in the tropical region). Males need more water than females due to more lean tissues in males and more adipose tissues in females.

When water cannot be ingested orally or by a feeding tube, it may be administered intravenously in the form of salt (saline) solutions, which closely resemble the electrolyte content of body fluids; dextrose solutions; or in blood or plasma as transfusions.

This is generally referred to as parenteral nutrition.

Water is absorbed rapidly because it moves freely through some membranes by diffusion. This movement is controlled mainly by osmotic forces generated by inorganic ions in solution in the body.

Water intoxication

This occurs as a result of water intake in excess of the body's ability to excrete water. Ensuing increased intracellular fluid volume is accompanied by osmolar dilution. The increased volume of intracellular fluid causes the cells, particularly the brain cells, to swell, leading to headache, nausea, visual impairment, vomiting, muscle twitching, and convulsions with impending stupor. If left untreated, water intoxication can be fatal.

But I can authoritatively tell you that water intoxication is most unlikely in the tropical regions of the world, where many have more water loss than intake. This is partly due to the pattern of diet, climate(mostly high temperature), low humidity, etc.

PERSONAL ADVICE

Make water intake habitual daily.

Regularize daily water intake; even when you are not thirsty, learn to habitually and frequently sip some water daily(especially occupants of the tropical regions).