Updated: Oct 19
Dana Eshelman, MS, RDN, CSSD, METS I
The human body is made up of 55 to 75% water and is an essential nutrient for survival. Water helps your body:
Regulate body temperature
Lubricate and cushion joints
Remove waste through urination, sweat, and bowel movements
Protect your spinal cord and other sensitive tissue
Digest food and transport nutrients to your cells
How Much Should You Be Drinking?
Well… it depends. Although there is no recommendation of how much plain water you need to consume on a daily basis, The National Academy of Sciences recommends men consume 3.7 liters and women 2.7 liters of fluids per day. This can come from plain water, decaffeinated beverages, and foods (soups, dairy, fruits and veggies). It is important to note, however, this is not a one size fits all approach. Everyone's fluid needs will vary based on your unique needs as an individual, your sweat rate and sweat concentration.
Points to consider when thinking about your fluid intake:
Daily activity - movement for 60+ minutes per day is reason to consider hydrating with carbohydrate and electrolytes
Sweat rate can vary based on individual as well as environmental factors. Drinking to thirst during exercise is an effective way to manage electrolyte balance and dehydration. I recommend drinking a beverage with some carbohydrate and sodium hydrate most efficiently.
Sweat sodium concentration
Environmental conditions - heat, humidity, altitude
Daily nutrition - consuming foods with higher water content are also hydrating
Body size will determine the amount of fluid you need per day. A larger body will need additional fluid in relation to blood volume.
Sweat rate varies considerably from person to person as well as for the same individual in different environmental conditions, training intensity, equipment/ clothing, genetics and heat acclimation. I recommend testing your sweat rate in a variety of conditions to help guide your hydration strategy in different scenarios.
Here is how to calculate your sweat rate:
pre training weight - measure weight after using the restroom and dressing down to comfort. Nude will give the most accurate data as the clothes you weigh in will accumulate sweat as you train.
post weight - measure weight after session, toweling off all sweat and removing clothing down to comfort. Again, nude is best.
Change in body weight
Volume of fluids consumed during activity - you will weigh the bottle you use before adding fluids to it, zero out scale, add fluids + electrolytes to it and record weight of fluids
Urine volume - you will need to measure any void done during activity. For ease of measurement, try to use the restroom immediately before the session.
Exercise time in hours
The next factor of sweat is that it is not just made up of water. Sweat is made up of water and electrolytes (sodium, chloride, magnesium, potassium, and calcium). The predominant electrolyte lost in sweat is sodium. An average sodium loss in sweat is 1000 mg per liter of fluids lost; however, it can range from 250 mg to 3000 mg per liter!
Factors that may influence sweat sodium concentration:
Sweat rate increases with increased intensity or energy expenditure as does the rate of sodium concentration in your sweat
Genetics - there is a gene called CF1 that determines how much sodium you lose in your sweat
You may be able to tell if you are a salty sweater if:
You have salt residue on your clothing, hat, and/or skin after a workout
Your eyes or cuts sting when it gets in them
Your dog or a friendly dog comes up to lick your legs after a training session
You have a head rush or get dizzy when standing up quickly after exercise
You crave salty foods during and/or after exercise
You suffer from muscle cramps during and/or after long or hard training sessions
How Do I Know If I am Hydrated?
The simplest way to tell if you are hydrated is by looking at the color of your urine. You are aiming for a pale, light yellow (like the color of lemonade). Dark yellow urine is a sign of dehydration; for example, your first void in the morning is more concentrated from not having fluids through the evening. Brown colored urine is a medical emergency and reason to seek medical attention.
Can I Drink Too Much Water?
There is risk for over hydrating with plain water which causes the concentration of sodium in your blood to become diluted. This causes your cells to swell and cause
As an endurance athlete, competing in marathons, ultramarathons, triathlons and long-distance, high intensity activities you are at higher risk for hyponatremia.
Premenopausal women are at the greatest risk of hyponatremia-related brain damage, which is thought to be in relation to female sex hormones' role in balancing sodium. Understanding your sweat rate and concentration can help you develop a personalized hydration protocol for during training; drinking to thirst is also a way to ensure you are not over hydrating.
What Level of Dehydration is Ok?
Dehydration is characterized as just 3% of body weight loss from fluid depletion. A 1-2% loss is associated with decreased cognitive function and psychomotor skills. A 3-4% loss decreases performance (muscle endurance and strength), increases respiration, and causes headaches, irritability, and sleepiness; it will also increase basal temperature in children. A deficit of 8% or more can cause death; however, there is some research showing athletes tolerating 10% deficit.
As an athlete, your ability to tolerate dehydration is highly variable on the individual and likely on different days in different climates. For premenopausal females, the level of dehydration tolerance can likely change throughout your menstrual cycle as well as basal body temperature increases during your luteal phase (second phase of your cycle).
Menopausal females also have higher incidence of dehydration as body water decreases about 6 liters (or 15%) between the ages of 20 and 80 years old. Thirst sensation also decreases which can make it more difficult to stay on top of hydration using internal cues. This is why as you enter menopause, you may be less tolerant to heat.
The American College of Sports Medicine recommends drinking enough during exercise to prevent <2% body weight loss from water deficit rather than drinking to 100% replace fluid losses. This can be determined based on your individual sweat rate.
Tips for Staying Hydrated:
Bring a reusable, insulated water bottle with you when you are out and about.
Hydrate early and often. It is best to sip on fluids throughout the day versus guzzle down large amounts in one go.
Drink 10-12 ounces of decaf fluids within the first 30 minutes of waking
Have a glass of water with meals
Add fruit such as berries, lime, lemon or orange to water to add some flavor
Sip on herbal teas, sparkling or seltzer waters as a part of your hydration
Add low fat or fat free milk; unsweetened, fortified milk alternatives or 100% fruit or vegetable juice into the mix for your hydration plan
Consume fruits and veggies as a part of a balanced diet
During training, include fluids containing at least 800 mg of sodium per liter. Optimally, testing your sweat rate and sweat sodium concentration in different scenarios (environment, intensities) and replacing fluids lost based on your individual objective and subjective data (thirst, salt cravings, fatigue)
Fuel fiercely so you can perform you best!