Sports Nutrition

Summer heat got you slowed down?

Summer heat and humidity can zap your energy levels and leave you feeling sick quickly when exercising outdoors. Staying well hydrated is the most important step you can take to keep from running out of steam and overheating. We begin to feel the effects of dehydration with just 1–2 percent of weight loss from fluid loss in sweat. For a 150 pound person, that is just 3 pounds of fluid loss during exercise. Heavy sweaters and those exercising outdoors during the summer months can easily lose this much or more in just one hour of exercise.

Dehydration happens when you lose fluid rapidly through sweat and don’t replace it by drinking enough. This causes your blood volume to drop to low which affects the body’s ability to get water to the surface of the skin for cooling the body. Signs of dehydration include sluggishness, dizziness, fatigue, nausea, high body temperature, and poor coordination.

To stay hydrated follow these simple guidelines:

  • Drink plenty of fluids throughout the day and with meals. This will help assure you are hydrated before you begin exercise. The American Dietetic Association (ADA) and American College of Sports Medicine (ACSM) recommend drinking 2 ½ to 3 cups of fluid 2-3 hours before exercise and 1 ½ cups 1 hour before exercise.
  • Plan to drink fluids during exercise. If you are exercising for more than an hour in the heat you will need to drink 8 ounces or more every 15 minutes depending on how much you sweat. A good rule of thumb is to take 8 full gulps to get about 8 ounces every 15 minutes. Carry water or a sports drink with you in a bottle or backpack. Know where the water fountains are in parks and on trails. A sports drink will help you stay hydrated better than plain water. The sweet taste will help you to drink more, ensuring better hydration, and the small amount of added sodium will help you absorb fluid into the blood stream faster. 
  • Replace fluid losses immediately after exercise. If possible, check your weight after exercise. For every one pound of weight lost, drink 2-3 cups of fluids. Low-fat milk, 100 percent fruit juice, smoothies, or sports drinks are all good options for replacing lost fluid. Milk may be the best choice. Research shows that the protein and naturally occurring electrolytes (sodium and potassium) found in milk actually helps replace fluid losses better than other fluids. Avoid alcoholic beverages as these may lead to more fluid loss due to their diuretic effect.


  • American Dietetic Association. Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. J Am Diet Assoc. 2009;109:509-527.
  • Roy, BD. Milk: the new sports drink? A review. J Int Soc Sports Nutr. 2008;5:15.

Author: Lona Sandon, M.Ed., R.D., Assistant Professor, UT Southwestern and American Dietetic Association Spokesperson

Posted: May 20, 2011