The Essentials of Daily Hydration

This article is an excerpt from Sports Nutrition for Endurance Athletes by Monique Ryan MS, RD, LDN, CSSD. In her comprehensive guide to sports nutrition, Ryan uses her 30 years of experience coaching professional and age-group athletes to simplify this complex subject into proven, real world guidelines. Sports Nutrition for Endurance Athletes shows runners, cyclists, and triathletes how to address specific nutritional needs for short- and long-course racing and busts dozens of myths and misconceptions along the way.

Water is one of the most essential nutrients for the endurance athlete. Some two-thirds of your total body weight is water, and this remarkable substance plays an important role in every major organ and system keeping you alive. We’ve all seen the need for hydration in a sweat-logged athlete. But for the athlete, the distraction of daily life can make it easy to forget to keep drinking water regularly. Many athletes also have not taken the time to learn and practice valuable daily hydration strategies. While much research and emphasis has been placed upon an endurance athlete’s fluid intake directly before, during, and after training or racing, emptying your bottles of fluid during a swim, bike ride, or run is only one of many hydration strategies essential for top performance. Paying attention to daily fluid intake during nonactive hours is also important. Nevertheless, daily water and fluid intake is often a secondary nutritional consideration, and many athletes frequently fall short on the everyday consumption of this life-sustaining nutrient.

Years of hydration research indicate that athletes should try to prevent even mild levels of dehydration. Although an athlete may not always be aware of how much he or she is sweating, even relatively small fluid losses during training and competition can be significant enough to hinder performance. And sweating doesn’t take place only during hot weather; it takes place in the gym, in cool weather, and during outdoor winter workouts as well. Studies demonstrate that even in thirst-inspiring hot weather, athletes usually fail to replace all the fluid that is lost through sweat during training and competition. To prevent any adverse performance effects, every athlete should arrive for training sessions optimally hydrated, and to do so means staying on top of your daily fluid intake.

Water: The First Nutrient

Much marketing fuss has been made about the optimal ingredients for the fluids that athletes require. But before the plethora of sports-related drinks and designer fluids flooded the market, there was simply water. Clear and calorie-free, water is basic and unpretentious and flows naturally into an active sport life with no packaging or gimmicks attached. Don’t take basic H2O for granted. Carbohydrates may be the premium fuel for your energy tank, but when you are about to train or compete in your sport, your fluid stores should be topped off as well. You can go a few weeks without food but will only survive a few days without water.

Water plays an integral role in the optimal functioning of your body both during training and during rest and recovery. Well-hydrated muscles are high in fluid content— in fact, water makes up 70 to 75 percent of an athlete’s muscle tissue. Fat tissue is relatively low in water content, at about 10 percent. Even bones, though seemingly solid, are about 32 percent water. Consequently, muscular athletes will have high water content when adequately hydrated. Water is stored in many body compartments, and it moves freely among these various spaces.

As the predominant component in our body, water performs many important functions:

  • About two-thirds of your body’s water is stored inside your cells, giving them their shape and form. The rest of the water in your body surrounds these cells and flows within your blood vessels.
  • Water is the main component of your blood. Blood carries oxygen, hormones, and nutrients such as glucose to your cells.
  • Water provides structure to body parts, protecting important tissues such as your brain and spinal cord and lubricating your joints. When fluids become depleted through sweating, both your cells and blood decrease in water content and volume.
  • Muscle glycogen holds a considerable amount of water, and water removes lactic acid from exercising muscles, which can be an advantage to well-hydrated athletes.
  • Water aids digestion through saliva and stomach secretions and eliminates waste products through urine and sweat. Water is essential for the proper functioning of all your senses, particularly hearing and sight.
  • As the primary component of sweat, water plays a major role in body temperature regulation. It enables you to maintain a constant body temperature under various environmental conditions because it allows you to continually make adjustments to either gain or lose heat.

Clearly the role water plays in maintaining your overall health is extremely important. That’s why you can’t live without water for more than a few days. But the role that water plays in your performance is equally vital. Being even slightly under-hydrated dramatically impedes top athletic performance.

Your fluid balance is simply the result of your intake of fluids versus your output of fluids. Intake is the net result of the water and other hydrating fluids we consume, the water in some of the foods we eat, and the metabolic water produced by our bodies. When you are not training, urine output represents your greatest fluid loss, or output, but sweating during exercise can result in significant fluid losses. Fluid is also lost in feces and in the air you exhale; through exposure to warm or humid weather, living in a dry climate, or living and training at altitude all increase fluid losses; and when traveling, especially by plane.

How much water do you need? Most people have heard the oft-quoted recommendation to consume eight 8-ounce cups of fluid (4 quarts, or about 1.9 L) daily, mainly in the form of water. In 2004, when much public attention was focused on dietary water requirements, the Food and Nutrition Board of the Institute of Medicine (IOM) released Dietary Reference Intakes (DRIs) for water and various electrolytes. Because of the large variations in water needs among individuals, the IOM panel established Adequate Intake (AI) levels of 130 ounces, or about 16 cups (3.8 L), daily for men and 95 ounces, or about 12 cups (2.9 L), for women.

But of course daily fluid losses can vary greatly depending on your level of training, whether you are male or female, and your individual sweat rate. The daily fluid needs of active males can increase to 4.75 quarts (4.5 L), but requirements for male endurance athletes can often be in excess of 10.5 quarts (10 L) daily, depending on sweat losses during training, and perhaps slightly lower for women. Estimating fluid requirements beyond the basic AI recommendations is really about replacing fluid at a rate close or equal to your own individual sweat rate and total sweat losses for a particular day of training. Further guidelines for replacing training sweat losses are provided in Chapter 5.

At rest, the fluids your body needs can be slowly replenished throughout the day as you make a conscious effort to drink enough water every one to two hours to replace these fluid losses. You should be aware, however, that climate, clothing, and other factors can affect daily water requirements. While thirst is often thought of as the primary human drive that pushes us to drink, it is important for athletes not to rely on thirst alone but to develop regular drinking habits and behaviors to maintain a good level of daily hydration and monitor their own hydration status. By the time someone becomes thirsty, his or her body has already sensed a decrease in the level of fluids or an increase in sodium concentration. So in reality, you get thirsty only when you have already experienced some fluid loss or alterations in your sodium status, both of which are affected by the prolonged periods of sweating that endurance athletes regularly experience. By then, an athlete’s performance level would already have decreased. So for an endurance athlete in training, one of the most important concepts to learn is that it is unwise to rely on thirst only for daily hydration needs. Doing so may result in falling short of both optimal fluid intake and optimal performance or recovery.

See what to eat and when with Sports Nutrition for Endurance Athletes. Ryan demystifies optimum daily nutrition and shows simple steps to make the best decisions about what you eat and drink.