As mentioned in the nutrition column for June10th, the Institute of Medicine (IOM) and National Academy of Sciencesrecently made recommendations for sodium intake that are targeted primarilyfor sedentary Americans. In this column we will take a look at a few keypoints regarding sodium and sodium sweat losses as it relates to enduranceathletes.The IOM has recommended that sodium intake be at 1500 milligrams daily.This recommendation is based on the fact that research supports that reducedintake of sodium coupled with increased potassium intake can help preventthe increase in blood pressure that occurs with aging.First it is important to appreciate that the daily sodium requirementsof athletes can vary widely due to sweat losses of sodium. Daily sodiumlosses in your urine are small- about 25 milligrams per day, and 100 mgfrom your skin. However, sodium sweat losses can vary greatly and be significantduring hard and long training sessions outdoors. Athletes have had measuredsodium sweat losses ranging from 460 to 1800 mg sodium per liter sweat.How much sodium you lose in an hour of training is also a product of yoursweat rate. Some well-acclimated triathletes and cyclists may be very efficientsweaters and lose only one-half to one liter of sweat per hour, while othersmay reach higher levels of two or three liters per hour in hot and humidweather, despite being acclimated.Clearly, endurance athletes need more sodium in their diet because theylose more sodium in their sweat. Sweat contains more salt when you arestarting to become acclimatized, and should decrease as you spend moretime training and racing in the heat. Depending on your sodium losses,which vary with your individual sodium sweat losses and the amount of hoursspent training, you can replace your sodium sweat losses with the saltor sodium in your daily diet and by consuming a sports drink with adequatesodium.For example, let say that you sweat about 1.5 liters per hour. In awell-acclimated athlete your sodium losses per liter may be about 750 mg.So in one hour you lose 1125 mg of sodium. If you train for three hours,your total sodium sweat losses are 3375 mg of sodium. Clearly the daysthat you put even more hours of training will increase your total sodiumsweat losses further. Having some salty foods and salting your food replacessome of the sodium lost in sweat.Besides having enough sodium in your diet, you can also consume a sportsdrink that contains adequate sodium. Check the sodium content of your favoritecarbohydrate-electrolyte beverage. Pay attention to how many ounces youconsume per hour and estimate your sodium intake per hour. You do not needto replace all of your sodium losses, but simply need to consume enoughsodium to prevent sodium levels from dropping too low.Besides focusing on your sodium intake during training, monitor yourhydration status after different training sessions that vary in trainingtime and intensity. Check your weight before and after training sessionsto measure how effectively you are able to keep up with ? or possibly exceed? your sweat losses. A weight loss of two to five pounds over the courseof a workout can indicate that you might need to increase your fluid intake.Conversely, if you actually gain weight during training, your drinkingmay be excessive. It is important to optimize your hydration, and sodiumintake, not maximize your intake beyond your fluid and sodium losses.
 Monique

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Monique Ryan, MS, RD is author of “CompleteGuide to Sports Nutrition,” and “SportsNutrition for Endurance Athletes,” from VeloPress. She is a regularcolumnist for Inside Triathlon and VeloNews magazines, andis founder of Personal Nutrition Designs, a nutrition consulting companybased in the Chicago area. Ryan regularly counsels athlete across NorthAmerica on performance and health-related nutrition concerns and offersservices through her website at www.moniqueryan.com.She is the nutritionist for the Performance Enhancement Teams forUSA Triathlon and the T-Mobile Women’s Cycling Team. She also consultedwith professional triathletes, the Saturn Cycling Team, and the Volvo-CannondaleMountain Bike Team. Ryan offers answers to reader’s questions twice monthly.Readers are welcome to send their questions directly to Ryan. The informationprovided in the “Feed Zone” does not constitute prescriptive nutritionaladvice. The information provided in this column is solely for general interestof the visitors to that site and is intended for educational purposes only.