Gatorology: The science of hydration, electrolytes and sweat.

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1 Gatorology: The science of hydration, electrolytes and sweat. Jeff Zachwieja, Ph.D. Principal Scientist Gatorade Sports Science Institute Barrington, IL

2 What benefits should a sports drink provide? Encourage drinking Speed rehydration Stimulate fluid absorption Improve performance

3 Myths & Misconceptions Thirst is a good indicator of fluid needs Sports drinks contain too much sugar Sports drinks make you fat Sports drinks rot your teeth Sports drinks contain simple sugars - bad news Sports drinks contain too much sodium Sports drinks are only good for exercise > 1 hour

4 Myths & Misconceptions Thirst is a good indicator of fluid needs Sports drinks contain too much sugar Sports drinks make you fat Sports drinks rot your teeth Sports drinks contain simple sugars - bad news Sports drinks contain too much sodium Sports drinks are only good for exercise > 1 hour

5 It is often stated in the lay press and even in professional journals that by the time a person is thirsty, that person is already dehydrated. In a number of scientific treatises on thirst, one finds no such assumption. Valtin, H. Drink at least eight glasses of water a day - Really? Is there scientific evidence for 8 x 8?. Am J Physiol 2002.

6 Diurnal Variations in Total Body Water Hyperhydrated Midnight Euhydrated Dehydrated Midnight

Sweat loss (liters) 2 29% How much they thought they lost. 1.83 0.99 How much they drank 0 0.53 0.

7 Sweat loss (liters) 2 29% How much they thought they lost How much they drank The appropriate physiological definition of thirst would seem to be the desire to drink resulting from a deficit of water However, thirst does not appear to be a sufficient stimulus for maintaining body water. Greenleaf, JE. Problem: thirst, drinking behavior, and involuntary dehydration. Med Sci Sports Exerc 24: , How much they thought they drank.

8 Why are many athletes poor drinkers? Inaccurate thirst mechanism Not stressed in their education Lots of other things going on Logistical limitations Choice of fluid

9 Myths & Misconceptions Thirst is a good indicator of fluid needs Sports drinks contain too much sugar Sports drinks make you fat Sports drinks rot your teeth Sports drinks contain simple sugars - bad news Sports drinks are no good for people with diabetes Sports drinks contain too much sodium Sports drinks are only good for exercise > 1 hour

Grams CHO per 8-oz Serving 40 30 20 10 How Much Sugar?

10 Grams CHO per 8-oz Serving How Much Sugar? 16% Cranberry Juice Cocktail 11.6% Orange Juice 10.8% Cola 6% Gatorade

11 Myths & Misconceptions Thirst is a good indicator of fluid needs Sports drinks contain too much sugar Sports drinks make you fat Sports drinks rot your teeth Sports drinks contain simple sugars - bad news Sports drinks contain too much sodium Sports drinks are only good for exercise > 1 hour

12 Benefits of Kcals Work harder Feel better Recover quicker Reduce hunger

13 The good news is that the calories in sports drinks are small.. And may be just the right amount to stave off hunger and motivate a workout. Kristine Clark, Ph.D., ACSM Health & Fitness Journal, September/October 1998

14 Melby et al. effect of carbohydrate ingestion during exercise on post-exercise substrate oxidation and energy intake. Int J Sport Nutr Exerc Metab 12: , females, y 500 kcal exercise or rest; 45 g CHO or placebo ad-lib buffet + dietary recall Fat oxidation decreased by CHO by 4.5 g CHO-Ex = 1470 kcal CHO-NoEx = 1285 kcal NoCHO-Ex = 1767 kcal NoCHO-NoEx = 1660 kcal

15 Myths & Misconceptions Thirst is a good indicator of fluid needs Sports drinks contain too much sugar Sports drinks make you fat Sports drinks rot your teeth Sports drinks contain simple sugars - bad news Sports drinks contain too much sodium Sports drinks are only good for exercise > 1 hour

16 Why aren t acidic foods & drinks a hazard to teeth?

17 Saliva!

18 Casamassimo & Hayes. Relationship between sports drinks and denatl erosion in 304 university athletes in Columbus, Ohio, USA. Caries Res 36:28-287, OSU athletes examined Lussi Index; blinded exam Survey on diet & dental habits 91.8% used sports drinks 36.5% had erosion No association with quantity, frequency, or years of sports drink use

19 Myths & Misconceptions Thirst is a good indicator of fluid needs Sports drinks contain too much sugar Sports drinks make you fat Sports drinks rot your teeth Sports drinks contain simple sugars - bad news Sports drinks contain too much sodium Sports drinks are only good for exercise > 1 hour

20 The Value of Sugar in a Sports Drink 1. Sweetness/mouthfeel 2. Stimulate fluid absorption 3. Source of exogenous fuel

21 Water follows solute. Net Water Flux in the Test Segment (ml h -1 cm -1 ) y = x r = Net Total Solute Flux in the Test Segment (mmol h -1 cm -1 )

22 The discovery that sodium transport and glucose transport are coupled in the small intestine was potentially the most important medical advance of this century. Lancet, 1975

23 Myths & Misconceptions Thirst is a good indicator of fluid needs Sports drinks contain too much sugar Sports drinks make you fat Sports drinks rot your teeth Sports drinks contain simple sugars - bad news Sports drinks contain too much sodium Sports drinks are only good for exercise > 1 hour

24 How Much Sodium? 1200 Milligrams sodium per serving Chicken Noodle Soup (1 cup) 1107 Chicken McNuggets (4 pieces) 340 Chocolate Shake (small) 250 Milk 120 Gatorade 110

25 Value of Sodium in a Sports Drink Stimulate drinking Maintain ECF volume Reduce urine production Speed rehydration

In laboratory tests that required about four quarts of sweat loss we found that thirst was temporarily satisfied by drinking as little as one pint of water. Dr.

26 In laboratory tests that required about four quarts of sweat loss we found that thirst was temporarily satisfied by drinking as little as one pint of water. Dr. David Costill, Professor Emeritus Ball State University, Buffalo News, 6/13/99 Rapid rehydration depends upon ingesting both the fluid and the sodium lost in sweat. Gary Mack, Ph.D. John B. Pierce Foundation Research Laboratories Yale University

27 Effect of Sodium Content on Voluntary Fluid Intake Rothstein et al. (1947) Nose et al. (1988) Wemple et al. (1997) % Increase Over Water

SODIUM INTAKE DURING EXERCISE REDUCES URINE OUTPUT 120 3-h cycling at 55% VO 2 max at 34ºC; 65%

28 SODIUM INTAKE DURING EXERCISE REDUCES URINE OUTPUT h cycling at 55% VO 2 max at 34ºC; 65% RH Water Urine Volume (ml/h) 60 Gatorade 0 Vrijens & Rehrer. J Appl Physiol 86: , 1999.

29 Myths & Misconceptions Thirst is a good indicator of fluid needs Sports drinks contain too much sugar Sports drinks make you fat Sports drinks rot your teeth Sports drinks contain simple sugars - bad news Sports drinks contain too much sodium Sports drinks are only good for exercise > 1 hour

30 Below et al. Med Sci Sports Exerc. 27: , Sprint-to-finish after 50 min cycling at 80%VO 2 max No fluid, no carbohydrate - worst time Carbo gel +6% Placebo (water) +6% Fluid &CHO +12%

Benton D. The impact of the supply of glucose to the brain on mood and memory. Nutr Rev 59:S20-S21, 2001. The human brain is an obligatory user of glucose.

31 Benton D. The impact of the supply of glucose to the brain on mood and memory. Nutr Rev 59:S20-S21, The human brain is an obligatory user of glucose. The assumption that the ability to transport glucose to particular areas of the brain never limits functioning may not be true. a glucose-containing drink improves memory in both elderly and younger humans. The provision of blood glucose has been found to improve the difficult but not easy trials of the Stroop test. Various studies have found that those with higher levels of blood glucose prior to starting a cognitive task perform it better.

32 Thanks for Your Attention!

Food and Fluid Intake After Exercise

Chapter 4 Food and Fluid Intake After Exercise When athletes finish a training session, nutrition is rarely the first thing on their minds. The intensity of the exercise often decreases appetite, so while