A Fluid Matter: Myths about Hydration

Myth: Thirst is a poor indicator of hydration.

Thirst is an excellent indicator of hydration status.  The body continuously monitors fluid and electrolyte balance through many redundant systems and triggers the thirst mechanism soon after dehydration begins to occur.  So long as urine output remains clear and copious, one can be pretty sure hydration issues are under control. 

That said, studies have clearly shown decreases in the thirst mechanism as we age.  Individuals between 67 and 75 years of age, when compared to 20- to 31-year-olds, have been shown to drink less water voluntarily after being deprived for 24 hours.1,2  Special attention should be paid to replenishing body fluids as we age. In addition, peak athletic performance can be compromised with even marginal losses in body water.  Athletes, especially in extreme conditions, must remain vigilant to water intake and urine output to strike the correct balance.

Myth: Sports drinks are necessary for combating dehydration.

The average person should NEVER consume a sports drink unless they have a bad case of diarrhea, are hung over, or exercise in the heat for more than 60 to 90 minutes. 

If you do not meet these qualifications then leave the sports drinks to LeBron James and Michael Jordan.  In most cases, all you are doing by sloshing down a bunch of sports drink during or after a workout is ensuring you slow down the fat-burning process, waste money, and pollute the environment.  Except for extreme athletes, ditch the sports drinks.  

Myth: The caffeine in coffee is a potent dehydrator and should be avoided before exercise.

Caffeine is a mild diuretic, but you will retain more water from consumed coffee than you will excrete.  Thus, it is unnecessary to avoid mild coffee or tea consumption (12 oz. or so) before exercise or competitions.  In addition, caffeine can actually enhance fatty acid mobilization and utilization. Not only that, but it has recently been shown to improve subjects’ perceptions of exercise. If you are a coffee drinker, feel free to sip a cup of Joe 45 minutes before a workout.  There are likely to be no real problems and there may even be some advantages.

Myth: Replenishing your body with the same amount of water lost during a workout, you will optimize your body for the next workout.

If given enough time, your body will tell you how much water to drink to rehydrate after exercise.  However, if you desire peak workout performance, optimal recovery, decreased drowsiness, and an enhanced ability to discern between hunger and thirst cues, there is a better strategy.

To appropriately rehydrate following a workout you must calculate your sweat rate by weighing yourself naked before the workout and after the workout and taking the difference between the two.  This is your sweat rate.  Then you must consume 150% of this weight of water to compensate for the lost body water. 

For example, if you weigh 150 pounds and lose two pounds during a workout, you would need to consume 48 ounces of water (3 lbs) to compensate for this lost water.  This “extra” water allows for the body’s recovery processes to occur optimally and prepares you for the next workout.

Myth: Beer is often served at post-race events because it is a good way to replenish carbohydrate stores and lost fluids.

Sorry, Anheuser-Busch, this is just dumb.  Alcohol acts as a diuretic in the body, making it a terrible choice for rehydration purposes.3  In addition, with only 14 grams of carbohydrate in a regular beer, (less in a lite beer), it is a pathetic choice for post-race glycogen replenishment.  Try water or some orange juice with salted pretzels after a long race.  You will be much better off.   

Myth: You weigh less in the morning because you burn off fat while you sleep.

You weigh less in the morning because you lose water weight through respiration and sweat while you sleep.  In addition, your body loses a small amount of weight through the exhalation of carbon atoms (CO2) in the expired air.

For optimal performance and alertness each day weigh yourself before you go to bed and again in the morning then replenish the lost weight with water.  You will be far less fatigued throughout your day.


1. Phillips, P. et al. (1984).  Reduced thirst after water deprivation in healthy elderly men.  New England Journal of Medicine, 311: 753-759.

2. Mack, G.W. et al. (1994). Body fluid balance in dehydrated healthy older men: thirst and renal osmoregulation. Journal of Applied Physiology, 76(4): 1615-1623.

3. Sherriffs, S. & Maughan, R. (1997). Restoration of fluid balance after exercise-induced dehydration: Effects of alcohol consumption.  Journal of Applied Physiology, 83(40): 1152-1158.