Myth or Fact: 8 Cups of Water Everyday

Eight cups of water every day… is a myth!  Just as you wouldn’t eat the same amount of food everyday as someone who is much smaller or larger than yourself, individual fluid needs vary.  As activity level and outdoor temperatures increase, the body requires extra fluids to replenish water lost via sweat.  Water intake can come in the form of coffee, tea, seltzer – any fluid except for alcohol, which dehydrates the body.  You can also “eat your water.”  Yes, certain foods have a high percent of water content, such as fruit and soup.  According to the Institute of Medicine (IOM), the majority of individuals will meet their hydration needs by letting thirst be their guide.  But older people (>65) lose their thirst response mechanism and can become dehydrated more easily.  Marissa’s Tip: don’t rely on thirst only.  Keep a 16 oz water bottle at your desk and fill it up at least three times outside of meals.  Remember you can also “eat your water” through fruits and vegetables!  Want to read more?  Go to my booth at the Full Engagement Center.

Show me the numbers!

You’re a numbers sort of person (clearly) and want to abide by a minimum amount of fluids per day.  Although the IOM does not specify an exact requirement for water intake, they do offer approximate guidelines that would include fluids coming from both food and beverages:

  • Women: Daily need of ~2.7 liters (91 ounces) – around 11+ cups/day
  • Men: Daily need of ~3.7 liters (125 ounces daily) – around 15+ cups/day

Water content in select foods

According to the Academy of Nutrition and Dietetics (American Dietetic Association just changed its official name), the following foods have a high percent of water content (when eaten raw):

1 cup = close to 1 cup of water

  • Strawberries: 91 percent water
  • Cucumbers: 96 percent water
  • Watermelon: 93 percent water
  • Lemons: 96 percent water
  • Leafy greens: 90 percent water
  • Tomatoes: 97 percent water

Athlete hydration needs

Exercise heats up the body – to counteract this, our body shunts blood to the skin tissues and begins sweating.  By sweating, we allow the body to release the heat build-up.  Sweat is made up of both water and electrolytes – if they are not replaced, then dehydration can result.  On the other extreme, too much fluid can result in a condition called, “hyponatremia,” which is when there is not enough salt in your body’s fluids.  Thus, knowing how to hydrate for your own body needs is CRITICAL to perform well.

The American College of Sports Medicine (ACSM) has established fluid guidelines for the athletic population.  The guidelines:

PRE-EXERCISE

  • The goal: pre-hydrate to start the activity with a normal level of hydration.
  • At least four hours before exercise, drink the following amount of water: take your weight in pounds and divide by 2.2 to get your weight kilograms (kg).  Multiply your weight in kg by 5 to get the amount of mL you need on the low end of the range.  Then multiply your weight in kg by 7 to get the amount of mL you need on the high end of the range.  For reference, 236 mL = 1 cup.
  • If you do not produce urine, or if the urine is dark yellow, about two hours before exercise you should slowly drink more beverage (for example, another ~3–5 mL per kg of body weight).
  • By hydrating several hours before exercise, you should have adequate urine output before the time that you will partake in activity.

DURING-EXERCISE

  • The goal: prevent dehydration; don’t over hydrate
  • Prevent <2% body weight reductions from baseline body weight.  Weigh yourself before exercise and after – if you are more than 2% less than the baseline weight, then you will need to increase fluid intake during exercise.
  • The amount you take in during a workout will vary based on the exercise you choose to perform.

POST-EXERCISE

  • The goal: replace all fluids and electrolytes lost during the activity.
  • ~1.5 L of fluid (6 cups) for each kilogram of body weight lost.
  • Fluids should have electrolytes in them (especially sodium and potassium).  If the fluids do not have sodium or potassium, then eat foods that do have these minerals.

References:

American College of Sports Medicine (ACSM). Sawka MN, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc 2007;39:377-390. (online version)

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