Editor's note: Fluids and Electrolytes - The Forgotten Nutrients, Part 2 is available here.
Most weight trainers and sports athletes know all the whys and wherefores of the necessity of essential nutrients like proteins, carbohydrates and fats, but sometimes forget that there are other nutrients that are also very essential for the body to work at optimal levels. Nutrients such as minerals and vitamins are two that readily spring to mind to many people but people tend to forget about the necessity of water and electrolytes.
Water is essential and one of the most important constituents of our body and water making up approximately 50%-70% of an adult's body weight. We also require a constant supply of water as all bodily functions depend on the balance of water, it is also required for normal functioning of the heart, the regulation of our body temperature and for other functions such as blood pressure, metabolic functions of all body cells, for the lubrication and cushioning of our joints, for the protection of our spinal column and ridding the body of wastes. Water is also a structural part of body tissues such as proteins and glycogen. Total body water can generally be divided into intracellular fluid and extracellular fluid components. Intracellular water comprises of all the water enclosed in cell membranes, while extracellular water is all the water outside body cells. Some of the extracellular water compartments include water in the plasma (intravascular water); water around the cells (interstitial fluid); water is also present in the gastrointestinal and urinary tracts, in the eyes and ears, and the cerebrospinal fluid (transcellular water).
The importance of fluid is so important that we can go weeks without food but if we go without water then death can occur in 2-4 days.
The majority of the fluid that we take in during the day comes normally from beverages such as water, canned drinks, milk, coffee and tea, but is also present in our solid foods, especially vegetables and fruit.
Of the total body weight, muscle and other organs comprise approximately 74 percent water, whereas fat only contains approximately 20 – 30 percent. The more muscle a person has the more water their body contains. Males generally have a higher percentage of water weight than females due to males having a higher percentage of muscle tissue. Females generally have approximately 10% less body water than males. As body fat contains very little water obese males may have only 50% of their body weight as water. And as we age our muscle mass generally declines and this decreases the percentage of water our body contains.
The functions of water in our body are numerous and some of these functions include water as being a natural lubricant that bathes every tissue in our body. Acting as a transport medium transporting nutrients, drugs, hormones, peptides, to our body cells. It is also important and necessary for the numerous chemical reactions involved in energy production. It also has an important function of removing any harmful waste from our body via the kidneys, and acts as a temperature regulator if our body is not cooled via sweating. If the body is not cooled it can cause us to suffer severe metabolic consequences.
The body has an intricate way of regulating our body fluids through stimulation of thirst and through the regulation of fluid loss through our kidneys. The body constantly assesses the fluid balance and adjusts our intake and output to maintain an optimum level of body water. An example of this is, if through exercise, our body creates sweat, this will cause blood volume to decrease, the body responds to this decrease by constricting the blood vessels to increase blood pressure and reducing any fluid losses from the kidneys, the body also stimulates a thirst mechanism. This thirst mechanism leads to the sensation of us having a thirst, but our feeling of being thirsty as an athlete only appears after a significant amount of fluid loss has already occurred.
Dehydration occurs when fluid losses exceed our fluid intake. If there is only a one percent or greater loss in body fluid then dehydration occurs. There are various stages of dehydration that occur ranging from mild, to severe dehydration, depending on the amount of fluid lost. Mild dehydration can be alleviated by responding to the feeling of being thirsty, but severe dehydration can result in death. The average adult can lose 2.5 litres of water every day through the processes of breathing, from waste removal from the body, and from normal sweating. Illness, vomiting, fever, diabetes, alcohol, exercise, being in a hot climate and just being too busy to drink may also lead to various stages of dehydration.
Symptoms of mild dehydration can be thirst, dry mouth, and headache, dryness of the lips and eyes, tiredness, feeling of light headedness, a decrease in urine output and weakness of the muscles. More severe symptoms of dehydration can include greater symptoms of the symptoms that are given above, plus a lack of sweating, gastrointestinal distress, and extreme thirst, dark concentrated urine with very few visits to the bathroom, sunken eyes and a fast heart beat, and low blood pressure. Dehydration over the long term can contribute to kidney stones, severe fatigue and also constipation.
As athletes most of the water that is lost comes from sweat through exercise, and also as vapour lost through our breath. Exercise and training can cause a substantial drop in body water levels and the threat of dehydration is very real. As one of the symptoms of dehydration is tiredness, and a loss of body water equal to only 5% of our body weight can reduce the muscular work capacity by as much as 20 to 30 percent, not good if we want results from our training.
Minerals such as sodium, chloride, potassium, calcium and magnesium form compounds that are dissolved in body water into electrically charged particles called ions. Pure water conducts electricity very poorly; ions dissolved in water carry electrical currents. We refer to these charged ions as electrolytes. The electrolytes can be both positive charged or negative charged and it’s through these electrolytes that the body maintains fluid balance. Although electrolytes are all found in foods, as athletes we often associate electrolytes as being in sports drinks. When we sweat, water, sodium and potassium is lost from the body, more water is lost via sweat than electrolytes, and as already mentioned any loss of body water is critical. Any loss of electrolytes can be corrected by adding a rehydration drink post workout, rehydration drinks contain electrolytes. Another method of replacing electrolytes is to add salt (sodium chloride) to the post training meal.
There are many factors that must be considered when drinking fluids. These include fluid volume, the frequency, its concentration, timing of the fluid intake, and the presence of electrolytes.
Many athletes consider themselves adequately hydrated just because they drink water while they train. For hydration to occur the water and electrolytes from our drink has to pass from the mouth to the stomach, it must then be emptied from the stomach, absorbed by the intestines (gastrointestinal tract) and reach the blood plasma and then the cells before they can become effective. So the rate of fluid passing from the stomach and absorbed by the intestines are important considerations, as our cells cannot benefit from the fluid and nutrients consumed until gastrointestinal absorption occurs.
Dehydration is common with athletes and can often be life threatening, often by exercising in a hot climate, dehydration can also occur in any training situation, including when training in the cold and in water. When athletes become dehydrated they fatigue early and use up muscle glycogen more rapidly, they also suffer an impairment of their ability to sweat and regulate their body temperature.
Loss of body weight from fluid losses has severe consequences with the ability to train at a high level. Up to 2% loss of weight decreases performance by 1.8 percent. 2-3 percent loss of weight decreases performance by 7%, 3-6 percent loss of weight causes cramps, severe thirst, and a 20 percent drop in performance, a greater loss of body weight of more than 6% will cause severe cramps, heat exhaustion, and possibly coma and death.
There are some athletes who voluntarily dehydrate themselves to make weight classes for competition. Some these athletes include boxers, rowers, wrestlers, and bodybuilders who not only drop water for a competition they also dehydrate themselves to improve their on stage appearance. Any voluntary dehydration can be reversed after the athlete has weighed in. If the voluntary dehydration is severe then these athletes may not adequately hydrate themselves before the competition. Some of the above athletes can also use diuretics to shed water weight; this is a severe practice that should be avoided at all cost. Diuretics not only cause fluid loss but also the loss of sodium and potassium, plus other electrolytes, causing an electrolyte imbalance and severe dehydration. People have died from the use of diuretics before or during competitions.
Athletes can be and often are confused as to the type of fluid to take in, should they use water or a sports drink? The method of hydration is dependant on the demands of training and also on the sport performed. A bodybuilder may choose water prior to training but a long distance runner would benefit from a pre race carbohydrate drink. How much to drink is dependant on the individuals ability to tolerate fluid in the stomach.
Sports drinks that are sold today to athletes generally contain a mixture of water, carbohydrates and electrolytes. Using these types of drinks athletes have to be aware of the concentration of carbohydrate in the fluid. A drink containing 6% - 8% carbohydrates (approximately 15 g of carbohydrates per 8 ounce serving) is used, as greater concentrations of carbohydrates would be emptied slowly and is a major cause of gastrointestinal distress in athletes.
A second category of drinks are high carbohydrate sports beverages. These types of drinks contain water, electrolytes and have more carbohydrates than the drink mentioned above. A 12 oz drink can normally contain approximately 70 grams of carbohydrates. This type of drink is normally consumed when athletes require a need for significant carbohydrates such as several hours prior to training, immediately after training or during a period of carbohydrate loading.
Another category of sports drinks is a called a meal replacement beverage, these types are normally consumed as a pre or post training meal, or as a meal replacement used when the athlete hasn’t enough time to sit down to a meal or have time or a place to cook. This type of drink can contain a mixture of high carbohydrates, moderate proteins, be low in fats and contain electrolytes.
Physiological processes of food and fluid intakes
Once food is in the body, several physiological processes occur; these include the gastric emptying, intestinal absorption, the possibility of gastrointestinal distress and the regulation of blood sugars. All these factors have to be considered to ensure that food and fluid intake enhances the athletes’ performance rather than diminishes it.
Gastric emptying is described as food that has entered the small intestine after being passed from the stomach. Food once eaten travels to the stomach where it mixes with hydrochloric acid and other digestive enzymes, this mixture is called chyme. There are many factors that can affect the rate that chyme empties from the stomach. One important factor is the volume of food or fluid. In most cases the larger the volume the faster the emptying process occurs, but there is a point at which the stomach cannot empty the contents any faster. Any food that remains in the stomach when performing exercise can make the athlete feel as though their stomach is full and feel heavy. Exercise intensity that is greater than 70% of VO2max will slow the release of the food mixture from the stomach. It is therefore important that the timing of meals has to be considered so that food has passed from the stomach before the start of any intense exercise. Exercise at intensity less than 70% of VO2max does not appear to affect the rate of gastric emptying. Another factor that affects how quickly chyme leaves the stomach is the composition of food. Protein and carbohydrates both leave the stomach at the same rate but fat moves out of the stomach more slowly and fats can take many hours to leave the stomach. Once food has passed through the small intestine, nutrients are absorbed within approximately 30 minutes. Exercise intensity of 75% of VO2max does not appear to slow intestinal absorption but intensities greater than 75% of VO2max causes a competition for blood flow between the active muscles and the gastrointestinal tract, which can cause a small increase in absorption time.
When only fluid is consumed, it immediately leaves the mouth and travels to the stomach. As the stomach absorbs very little water, fluid leaves the stomach very quickly. Three factors that affect the rate of gastric emptying from the stomach are exercise intensity, fluid volume, and nutrient composition. Exercise at an intensity of 75% of VO2max or greater slows gastric emptying. Larger volumes of water between 400 and 600 ml leave the stomach faster than smaller volumes. So sipping water throughout an exercise session may not be the best method for fluid intake, but is better than none at all.
Adding carbohydrates or sodium to water changes the concentration (osmolality) of the solution. If the concentration is too high, then gastric emptying is delayed. Carbohydrate beverages should contain less then 8% carbohydrate to reduce any delay in gastric emptying. Adding carbohydrate and sodium to water speeds up its absorption and so is advantageous. Although adding carbohydrate to water reduces gastric emptying, the time delay is offset by the rate of gastrointestinal absorption.