As a Registered Dietitian, people seek my advice on living a healthy lifestyle. I am often asked ‘What is the one thing I can do to lose weight?’ from my dieters, ‘What is the one thing I can do to maximize my athletic performance?’ from my athletes and ‘What is the one thing I can do for better health?’ from my general public. The answer is simple and one answer can help achieve all these requests. Simply put – stay hydrated.
Adequate daily hydration is necessary for all, regardless of activity level or health condition. Dehydration can be masked as hunger. Staying properly hydrated is an important component to healthy weight loss and/or maintenance. Maintaining proper fluid levels aid in electrolyte balance, joint health, organ function and blood flow/volume. However, I see the greatest need for fluid assessment in my active clients.
Hydration is not a ‘one size fits all’ concept. Adequate hydration for one may mean copious amounts of fluids for the extremely active and heavy sweater or more restricted fluids due to a disease state that can be exasperated from too much fluid. Activity level, body size and environment are all important factors when assessing adequate fluid needs.
The 2005 Dietary Reference Intakes (DRI) for Water and Electrolytes outlines the adequate intake for gender, age and life stages (1). For the average adult, living a sedentary lifestyle, DRIs suggest a daily AI of 2.7 L (~11.5 cup) for females and 3.7 L (~15.75 cup) for males. This consists of water provided by beverages, foods and drinking water. The most common assessment for adequate hydration and fluid replenishment is to observe urine color and quantity. The lower the volume and darker the color, the more effort one needs to put into rehydrating. Pale color generally indicates adequate fluid balance (2)
For the athlete, overly active or those with jobs that must endure extreme heat, fluid needs are increased. Sweat level and environmental conditions have an impact on hydration needs. Light sweaters may require only modest volumes of fluid intake (<750 ml/hr or 24 oz/hr) whereas heavy sweaters may have to ingest in excess of 1.5 L/hr or ~50 oz/hr. In warm environments, daily water needs can be considerably larger and might increase to more than 10 L/day (3). One should consume ~1 oz water or sports drink/10 lb body weight 2 hr before exercise or heavy activity. If profuse sweating is expected, drink an additional 0.6 oz per 10 lb body weight within 20 minutes before exercise.
The greater the weight loss percentage due to fluid loss, the greater the harmful impact on the person. A 6% loss in body weight due to fluid loss could result in heatstroke and even death. Sweat rate is easily assessed by recording body weight before and after activity – weight loss indicates inadequate drinking, weight gain indicates excessive drinking. However, there is no need to drink large volumes of fluid before exercise either. This can actually be more harmful than beneficial.
Sweating is our body’s method of cooling itself. Most athletes will lose between 1 and 2 liters of sweat per hour of exercise, and some are capable of sweating more than 3 L/hr (3). Sweat increases electrolyte loss. In addition to fluid replenishment, electrolytes lost during activity must be adequately replenished.
Most sports drinks provide adequate electrolyte replenishment and should be considered as a potential hydration source. In addition to electrolytes, sports drinks provide a low level of sodium, which can help to drive thirst, thus driving the need to drink and achieve hydration. When choosing a drink, your best choices are water, sports drinks, milk and 100% juices. Alcohol, energy drinks and sodas are poor choices and harmful.
To summarize – drink ~16 oz 2 hr prior to activity or exposure to extreme heat. Drink 8-16 oz 15 minutes before activity. During activity or heat exposure, drink enough to minimize loss of body weight without over drinking. Ideally, drink 4-8 oz every 15 minutes. 1 medium mouthful of fluid is ~ 1 oz. After activity, drink 25 oz/lb body weight lost during activity. Your goal is to consume 150% of weight lost within 6 hr post activity. Choose water or a sports drink for your fluid needs before, during and post activity.
By Randi Boleman, PhD, RD, LD, CSSD
- National Academy of Sciences, Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. 2005. Washington, DC, National Academies Press. www.nap.edu
- Clark, N. Sports Nutrition Guidebook. 2003. Brookline, MA. SportsMedicine Associates.
- Dunford, M. Sports Nutrition: A Practice Manual for Professionals, 4th Edition. 2006. American Dietetic Association; Sports, Cardiovascular & Wellness Nutritionists Dietetic Practice Group.