Weight loss during dieting does not normally provoke dehydration. However, weight loss due to water loss during exercise, illness or exposure to heat does result in dehydration of body tissues. Human bodies contain over 60 percent water, with blood having 92 percent, bones 22 percent, brains and muscles 75 percent, and fat 10 percent water. The body does not tolerate dehydration well. Loss of 10 percent of body mass in fluid can result in death.
Types of Dehydration
Types of dehydration are classified according to the balance of water and electrolyte loss. Body fluids have mineral ions such as sodium and potassium dissolved in them, so when water is lost, the electrolytes go with it. Hypertonic dehydration is when more water is lost than sodium. This occurs during periods of profuse sweating. Isotonic dehydration occurs when equal amounts of water and electrolytes are lost, as in vomiting and diarrhea. Hypotonic dehydration has more sodium loss than water loss and occurs in improper rehydration after isotonic dehydration.
Water Loss
Water is routinely lost during respiration, as well as through urine, feces and sweating. During exercise, the body becomes heated due to the burning of fuel. Your body responds by sweating to cool down. If the exerciser is exposed to high ambient temperatures during exercise, sweating increases even more. Some athletes can lose more than 1.5 liters of sweat in an hour. Since breathing increases with activity, more water is lost through respiration as well. It is estimated that ideal water consumption to maintain proper hydration is 1 to 1.5 ml of water per kilocalorie burned, or 1 to 1.5 liters if 5,000 calories are burned during exercise.
Symptoms
In "Nutrition and Diet Therapy Reference Dictionary," Rosalinda Lagua and Virginia Claudio identify the consequences of losing the following amounts of body mass due to dehydration in a 24-hour period. If a 3-percent loss occurs, physical performance and blood volume decrease. A 5-percent loss may cause nausea and difficulty concentrating; an 8-percent loss can cause dizziness, loss of thermoregulation and weakness. At a 10-percent loss, lowered kidney blood circulation can result in kidney failure. Paul Insel and colleagues stated that dehydration of more than 3 to 5 percent of body weight can increase core body temperature, affect electrolyte balance, and lead to heart and kidney changes. Cramps, heat exhaustion and heat stroke can result.
Competition
Volker Nolte in "Rowing Faster," stated that dehydration of more than 2 percent of your pre-performance body mass to "make weight" in rowing may affect performance even if rehydration is attempted. Weigh-in procedures were altered for collegiate wrestlers after three healthy athletes died in 1998. They underwent significant pre-season weight loss followed by losing 3.5 to 9 lbs. one to 9 hours before their deaths by restricting food and fluid and exercising in hot ambient temperatures wearing gear that restricted sweating. William McArdle et al., in "Exercise Physiology," cited that at a 4.3-percent water loss, walking endurance decreased 48 percent..
Rehydration
It is not enough to just drink water after dehydration. The lost electrolytes also have to be restored. Nolte recommends eating small quantities of salty foods along with plain water. Sports drinks containing electrolytes and salt are another option.
References
- The Water Information Program: Water Facts
- "Rowing Faster"; Volker Nolte; 2005
- "Nutrition and Diet Therapy Reference Dictionary"; Rosalinda Lagua and Virginia Claudio; 1996
- Montana State University: Sports Nutrition
- "Exercise Physiology"; William McArdle et al., 2009
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