1.4 Translation of Dietary Assessment into Analysis
1.4.5 Fluids and Hydration
Water makes up 50–60% of our body weight. Water is essential for many of our body functions, including heat regulation, participates in chemical reactions, and is used as lubrication, as a transport medium, and as a solvent during ionization of electro- lytes and acids. Body water is found most abundantly in the skin, organs, muscle, and blood. Thus, hydration by water as well as other beverages before, during, and after physical activity is essential to maintain a healthy lifestyle and peak performance.
This section addresses fluid replacement and the role of water and sports drinks in hydration as well as the influence of hydration on physical performance.
The American College of Sports Medicine’s position stand for exercise and fluid replacement states the following: (1) prehydration is essential and should begin sev- eral hours prior to exercise, (2) develop a plan for fluid replacement during exercise that will prevent more than 2% dehydration, (3) fluid held at a temperature between 15 and 20°C will be preferred over warmer beverages, (4) consume fluids containing 20–30 milliequivalents per liter of sodium, 2–5 milliequivalents per liter of potas- sium, and 6–8% of carbohydrates to help sustain electrolyte balance and exercise performance, and (5) consuming beverages with meals postexercise will expedite rapid and complete recovery due to the stimulation of thirst and fluid retention.114 1.4.5.1 sports drinks
When sports drinks were developed, they changed the way athletes hydrated before, during, and after events. Sports drinks are made up of three main components: water, carbohydrates, and electrolytes.115 Carbohydrates and electrolyte replacement, in addition to water replacement, is important to assist the body in recovery, especially after prolonged exercise as well as performing in a hot, humid environment. Table 1.5 lists some popular sports drinks and their relation to other beverages, such as water, orange juice, and diet and regular soft drinks. As discussed previously, it is important to understand what an individual is consuming prior to, during, and after exercise to determine if he or she is adequately hydrating and replenishing fluid stores.
The form and concentration of carbohydrates contained in drinks have been stud- ied extensively to determine which would assist in performance and replenish stores.
Some carbohydrates have led to gastrointestinal upset and as such may not be a good recommendation for athletes. However, since every individual is different, it is important to try different sports drinks during training to determine which, if any, work best for the individual. Gisolfi and colleagues (1998)117 used different formulas of carbohydrates to determine if the beverage osmolality would have any effect on gastric emptying and thus affect water availability. Each beverage contained 6%
carbohydrates but with different formulas. The carbohydrate beverages were not dif- ferent in comparison to gastric emptying; however, the water that was consumed in the control group was absorbed faster.117
40Nutritional Assessment of Athletes, Second Edition
tAble 1.5
Carbohydrate-electrolytes beverages versus Water
beverage Carbohydrate Ingredient
Carbohydrate (% concentration)
grams of
Carbohydrate sodium (mg) potassium (mg) Gatorade Thirst Quencher
(Gatorade Company)
Sucrose, glucose, fructose 6 14 110 25
Gatorade Endurance Formula Sucrose, glucose, fructose 6 14 200 90
PowerAde (Coca-Cola Company) High-fructose corn syrup, maltodextrin
8 19 55 30
All Sport (Monarch Beverages) High-fructose corn syrup 9 21 55 55
Coca-Cola High-fructose corn syrup, sucrose 11 26 9.2 Trace
Diet Soft Drinks None 0 0 0–25 Low
Orange Juice Fructose, sucrose 11 26 2.7 510
Water None 0 0 Low Low
Gatorade Energy Drink (Gatorade Company)
Maltodextrin, glucose, fructose 23 53 133 70
Source: Modified from Williams, M.H., Nutrition for Health, Fitness, and Sport, 8th ed., McGraw-Hill, New York, 2007.
1.4.5.2 Water
As discussed above, water is able to be absorbed quicker than the 6% sports drinks, resulting in more rapid replenishment, which would be vital during exercise under certain conditions. Ryan and colleagues (1998)118 also found that consuming water during exercise, even when an individual is hypohydrated, had a slightly higher absorption than different carbohydrate drinks.118 However, there are many different aspects that can affect gastric emptying. The main aspects are exercise intensity, the pH of the stomach, mode of exercise, volume of fluid, caloric density, drink tempera- ture, electrolytes, heat stress, and osmolality. Since water plays a vital role within the body, it is important to replenish fluid stores and to stay adequately hydrated.
Therefore, when considering hydration for training and performance, water is a cheap and easy option, and it should not be dismissed in preference to sports drinks.
1.4.5.3 other beverages
As seen in Table 1.5, other beverages have been used to assist in hydration. Soft drinks are one option that athletes may choose due to their high carbohydrate con- tent. This choice is often a matter of taste preference, however. It should be noted that many soft drinks contain caffeine, which is considered a diuretic and may negatively affect hydration status. Likewise alcoholic beverages are inadvisable for the same reason.119 Fruit juices, on the other hand, not only provide a good source of water but also may have higher content of carbohydrates. This may be advantageous for some individuals; however, juice consumption is very individualized and care must be taken since some individuals may have gastrointestinal upset due to lower pH of the juices.
1.4.5.4 fluid hydration status
Hydration status may be categorized one of four ways. First, dehydration results when the body fluid volume is decreased. The term hypohydration is also used in similar situations as dehydration and is defined as the rate of fluid intake that is less than the rate of fluid loss. Dehydration or hypohydration has been shown to impair exercise performance and can lead to detrimental effects on the individual if not corrected. Voluntary dehydration, which has been used by some athletes to qualify for a lower weight class, could have a possible detrimental effect on per- formance. Research clearly shows that voluntary dehydration does not improve performance and may affect cognitive functioning.120 Involuntary dehydration occurs most often during prolonged aerobic activities and can have a major effect on performance and, more importantly, on health. When individuals become dehydrated, cardiovascular functions and temperature regulation often become compromised and physical performance may be adversely affected114; as seen in more severe cases, an athlete may have a reduced sweat rate121 and heat illness may result.
Second, hyperhydration reflects a status where the rate of fluid intake is greater than the rate of fluid loss. This can be helpful in regulating body temperature and cardiovascular functions when the rate of fluid intake during performance cannot keep pace with the rate lost during exercise.122 While there is no evidence to suggest
42 Nutritional Assessment of Athletes, Second Edition
that hyperhydration improves performance per se, hyperhydration prior to some distance events performed in hot, humid environments may minimize performance decrements. Therefore, the American College of Sports Medicine recommends that hyperhydration be used before exercise or performance in heat environments.61 Cold water or a glucose–electrolyte solution can assist athletes in hyperhydrating.116
Euhydration is defined as the rate of fluid intake that is adequate to replace fluid losses. It is important for athletes to be euhydrated or, in certain circumstances, hyperhydrated prior to exercise or an event. Being properly hydrated helps in mini- mizing fluid loss and performance, and may prevent heat-related illness.116
Rehydration results when an individual consumes fluids in an effort to replen- ish fluid lost during an event that has caused the body to be in a dehydrated state.
Rehydrating can also reduce the rise in body temperature and minimize the stress on the cardiovascular system during longer periods of endurance exercise.116
It is critical for athletes to rehydrate following exercise training or competition to ensure proper performance during the next day’s training or event. As mentioned in Section 1.3, rehydration is needed and can be simple using the correct tech- niques. Being aware of the amount of time available for rehydration is imperative.
It is important to weigh prior to exercise and then immediately after. By comparing these numbers, rehydration can be determined. For each kilogram lost, a person should consume 1.5 liters of fluid if needing to rehydrate in a short period of time, approximately 12 hours.123 Plain water with food that contains sodium to assist in the replacement of electrolytes will be able to adequately rehydrate an athlete who has an extended amount of time for rehydration.