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Exercise and Obesity
Rates of walking and cycling were analyzed in 14 countries. Rates were highest in Switzerland, the Netherlands, and Spain, and lowest in the US, Australia, and Canada. Not surprisingly, the rates of diabetes and obesity were lowest in the countries where people did the most walking and cycling. (source: Am J Pub Health, Oct. 2010)













 
 

Why Sports Nutrition is Different

Author: Stan Reents, PharmD
Original Posting: 05/06/2007 01:29 PM
Last Revision: 07/20/2017 02:14 PM

The Federal government publishes nutrition guidelines every 5 years. The latest set, Dietary Guidelines for Americans, 2015 were released in January 2016. In June, they made a downloadable PDF available here: "Dietary Guidelines for Americans, 2015."

In this discussion, I will explain four of these dietary guidelines that need to be modified for athletes and other active people.

CARBOHYDRATES

In the past, many consumers have been led to believe that all carbohydrates are bad. While a little more sanity seems to have returned since then, there are still many who believe that carbohydrates should be avoided for one reason or another.

Carbohydrates are the easiest fuel for your body to utilize. For this reason, as exercise intensity increases, your muscles preferentially burn carbohydrates for energy.

Unfortunately, your body only stores about 2000 carbohydrate calories (compared to 50,000 or more as fat!). So, during prolonged exercise, you will run out of carbohydrate energy reserves long before you deplete your fat reserves.

What this means is that, if you are on a long bike ride, running (or walking) a marathon, or playing a 3-hr tennis match, you need to ingest carbohydrates while you are competing. Athletes know to consume carbs every 20-30 minutes during prolonged competitions like these. Carbohydrates need to be resupplied regularly because they are so easily depleted.

The 2015 Federal Dietary Guidelines for Americans suggests that your daily calories should be consumed as follows:

  • Carbohydrates: 45-65%
  • Fats: 20-35%
  • Protein: 10-35%

However, these percentages don't apply to athletes. In Food For Fitness - Eat Right to Train Right, author, coach, and former elite cyclist Chris Carmichael recommends a diet that provides 60-70% of daily calories from carbohydrates during strenuous and/or prolonged exercise.

So, general nutrition guidelines recommend a diet that provides 45-65% of daily calories as carbohydrates, while sports nutrition experts recommend 60-70% of your calories come from carbohydrates. Which one is correct?

The Federal Guidelines don't pertain to elite endurance athletes. One reason for the lower carbohydrate ratio suggested in the Dietary Guidelines is to acknowledge recent evidence showing that dieters can lose weight on higher-protein diets. By allowing for a higher percentage of calories from protein, the percentage of carbohydrates is less.

Another distinction is the total number of calories consumed per day. An overweight person who is dieting and not exercising vigorously may be consuming only 1200-1500 calories per day. However, elite athletes like Tour de France cyclists burn up as much as 9000 calories in a single day. To provide 9000 calories per day, a diet with less than 60% carbohydrates would contain too much fat and too much protein.

The final distinction to be made is that, for general health benefits, carbohydrates should be complex, eg., consumed as fruits, vegetables, whole grains, etc. However, during strenuous exercise, simple carbohydrates such as glucose, sucrose, and fructose are needed because these are rapidly-absorbed.

So, to summarize, carbohydrates are important for both athletes and non-athletes. In sedentary people who want to lose weight, the carbohydrate portion of the diet can be as low as 45%, to allow for a higher ratio of protein-to-carbs. But, during vigorous exercise, carbohydrate intake should rise to 60-70% to provide the energy that exercising muscles need.

FRUCTOSE

If there is one dietary substance with a Dr. Jekyll and Mr. Hyde image, it might be fructose.

Over the past 40 years, food processors in the US have gradually shifted away from using sucrose (table sugar) as a sweetener in favor of using corn syrup. Corn syrup is easier for manufacturers to use and is cheaper. Further, fructose is sweeter than sucrose. So, fructose was added to corn syrup (aka: "high-fructose corn syrup"), and in ever-increasing amounts. Today, corn syrup in solid foods (eg., cookies) contains 42% fructose and corn syrup in liquids (eg., soda pop) contains 55% fructose (Elliott SS, et al. 2002). HFCS is routinely used in many artificially-sweetened, fruit-flavored snacks and beverages. But, it is also found in foods that might surprise you, such as multi-grain bagels, spaghetti sauces, chocolate milk, yogurt, Coffee-Mate coffee creamer, Fig Newtons, and many other sources.

As more and more data are collected, it appears that fructose is a major health concern (Bray GA, et al. 2004) (Havel PJ. 2005). The Dietary Guidelines for Americans don't specifically address high-fructose corn syrup. However, other groups are very concerned about this food additive. On July 13, 2005, the Center for Science in the Public Interest (www.cspinet.org) filed a petition with the FDA requesting that "health notices" be placed on the labels of soft drinks.

The reason why obesity researchers believe HFCS is bad is because fructose does not stimulate an insulin response that typically occurs when you ingest other sugars such as sucrose, glucose, lactose, etc (Elliott SS, et al. 2002) (Teff KL, et al. 2004). Without triggering insulin output, another hormone known as leptin is not released. And without a normal insulin-leptin response, the brain does not receive the proper signal to stop eating. In other words, when you eat a 600-calorie meal, and 100 of those calories come from fructose, your brain perceives the meal as containing only 500 calories.

Elite endurance athletes like Tour de France cyclists and Iron Man competitors consume tons of PowerBars and sports drinks during competition. But, if you look at the label for PowerBars, the first ingredient listed is "high fructose corn syrup". And, if you analyze the carbohydrate sources for sports drinks, you also find fructose. Besides, nature gives us fructose in such wholesome foods like bananas, so, is fructose really bad for us?

As mentioned above, for optimum performance, carbohydrates must be supplemented during prolonged exercise because glycogen stores can be depleted long before fat stores are. And, these carbohydrates should be simple, not complex. Regarding the fructose found in sports drinks, four decades of research has revealed that using several different carbohydrates together allows for better absorption than if the product was formulated with only a single carbohydrate. For example, Gatorade® is made from a mixture of sucrose syrup and glucose-fructose syrup.

Second, ingesting excessive amounts of anything, even a naturally-occurring substance such as fructose, is never a good idea (though, high-fructose corn syrup is hardly what one would call a "natural" substance!). Note that non-diet sodas contain 80% more sugar -- as high-fructose corn syrup -- than sports drinks like Gatorade®.

So, the bottom line is this: if you are attempting to lose weight, you should definitely try to avoid food products sweetened with HFCS. Athletes and others who exercise regularly don't need to worry about the fructose in bananas or sports drinks.

SODIUM

Most people have probably heard the medical profession's recommendation to limit the amount of sodium (salt) in our diets. This is because sodium causes fluid retention and raises blood pressure. Limiting sodium intake is especially important for people with conditions like hypertension, congestive heart failure, and certain kidney diseases. Blacks should also limit their sodium intake because they are more sensitive to its effects than other races.

The 2015 Dietary Guidelines recommend the following:


GROUP MAXIMUM SODIUM INTAKE
PER DAY
• Otherwise Healthy Adults 2.3 grams per day
• Blacks, Elderly, People with Hypertension 1.5 grams per day

However, during strenuous exercise, athletes can lose 1 gram (or more) of sodium per hour. Thus, their sodium requirements can be much higher than 2.3 grams per day.

Further, if sodium loss is coupled with the consumption of large volumes of plain water, a condition known as "hyponatremia" can occur. (Translated, this term means "a low concentration of sodium in the blood.") Hyponatremia can cause confusion, disorientation, seizures, and can even be fatal.

While anyone who drinks too much plain water while perspiring can develop hyponatremia, especially at risk are cyclists (because it is easier to drink while riding a bike than while running), females, and marathon-walkers (because perspiration -- and water consumption -- occurs over a longer period).

So, athletes, and, for that matter, anyone who is perspiring heavily over a prolonged period of time, should not limit their sodium intake. In fact, they may need to increase it. However, check with your physician first if you have any of the medical conditions listed above.

WATER

You may have heard the recommendation to drink "8 glasses of water per day." However, that recommendation has no scientific basis.

So, to address this, a panel of experts from the US and Canada was convened on behalf of the Institute of Medicine to determine optimum fluid intake requirements for adults. Their excellent report was made public in February 2004. Recommendations on fluid intake are listed below:

For healthy sedentary adults living in temperate climates:

  • Men: 125 oz (3.7 liters) of water per day from all dietary sources
  • Women: 91 oz (2.7 liters) of water per day from all dietary sources

For most people, this amount of water per day is a lot more than they normally drink. The requirement for men is roughly 1 gallon per day. How many of you men out there drink this much water every single day? For the women, 91 ounces is roughly 3 quarts.

However, an exercising athlete can lose enormous quantities of body water through perspiration. The recommendations listed above don't apply to endurance athletes.

So, then, how much should athletes drink? Unfortunately, there is no single answer that applies to all athletes because sweating rates for different sports can vary enormously. For example, researchers from West Chester University in Pennsylvania determined that cross-country runners should consume 4.6 liters of fluid per day and that football players require as much as 12.2 liters per day (Godek SF, et al. 2005).

In the past, the guideline was to "drink as much as you can." However, with over 70 cases of hyponatremia documented in athletes, the sports medicine community has recently changed their recommendations for hydration. Now, athletes are cautioned to be more moderate in the amount of water they consume (during competition or training). The International Marathon Medical Directors Association (IMMDA) released a statement in 2002 that marathon runners should drink no more than 400-800 ml per hour. That's 13 - 26 ounces.

That's a good rule-of-thumb, but the best rehydration formula is based on an athlete's own specific sweat rate. The athlete records how much their weight changes and how much they drink during a specific duration of training, say, 60 minutes. (This formula can be obtained at the USA Track & Field web site, or, refer to the story Fluids and Electrolytes During Exercise.)

And because of the risk of hyponatremia, at least some of the fluid replacement should be with a sodium-containing sports drink, though, it should be noted that many brands of sports drinks actually contain relatively small quantities of sodium. Several sports drinks are listed below, in descending order based on sodium content (all quantities are per 8-oz. serving, except as noted):


PRODUCT SODIUM
(per 8-oz.)
CAFFEINE?
Gatorade Endurance Formula 200 mg no
PowerBar Endurance Sport (18 g powder) 160 mg YES
Gu2O 120 mg no
Aquis 110 mg no
Gatorade Thirst Quencher 110 mg no
Revenge Sport 100 mg YES
Powerade, orange 55 mg no
Cytomax 50 mg YES
Ultima Replenisher 37 mg no
Powerade Mountain Blast (20 g powder) 25 mg no

SUMMARY

Athletes have a much different requirement for the following four nutrients compared to the average adult:

Carbohydrates: The key to a good diet is balance. Carbohydrates are not bad, though too little, or too much might be. Whether you are an endurance athlete or not, carbohydrates should represent the largest percent of your daily calories. Shoot for 45-65% at a minimum, and up to 60-70% during periods of regular, strenuous exercise.

Fructose: Because fructose does not trigger the normal insulin-leptin response, dieters should attempt to avoid all food products sweetened with high-fructose corn syrup. However, athletes and other active people should not worry about energy bars or sports drinks that might contain fructose, unless that particular product causes GI intolerance.

Sodium: For the general population, a daily maximum of 2.3 g of sodium is recommended (1.5 g for blacks, elderly, or people with hypertension). However, during exercise that lasts longer than 60 minutes, especially if you are a "salty sweater," sodium requirements will be much greater than 2.3 g per day.

Water: In general, most adults need to increase the amount of water they drink each day. However, athletes need to drink an amount that matches their sweat rate, which can be substantially greater than the recommendations in the Federal Dietary Guidelines. Further, in athletes, at least some of the fluid intake should come from sports drinks that contains sodium. Or, alternatively, athletes should try to eat some salty pretzels.

FOR MORE INFORMATION

One of the best sports nutrition books I have read is Food For Fitness - Eat Right to Train Right by Chris Carmichael (2004). Even though this book is intended for serious endurance athletes, it provides a lot of common-sense information. The book is very easy to read, so average people don't need to worry about trying to understand a lot of complex biochemistry. I can highly recommend this book for anyone who wants solid, practical information on sports nutrition, and, healthy eating in general (see Book Reviews).

For more information on fluid requirements during exercise, go to www.USATF.org.

The federal government's "Dietary Guidelines for Americans" can be found at: www.Health.gov: Dietary Guidelines for Americans, 2015

Readers may be interested in the following related stories:

EXPERT HEALTH and FITNESS COACHING

Stan Reents, PharmD, is available to speak on this and many other exercise-related topics. (Here is a downloadable recording of one of his Health Talks.) He also provides a one-on-one Health Coaching Service. Contact him through the Contact Us page.

REFERENCES

Bray GA, Nielsen SJ, Popkin BM. Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity. Am J Clin Nutr 2004;79:537-543. Abstract

Elliott SS, Keim NL, Stern JS, et al. Fructose, weight gain, and the insulin resistance syndrome. Am J Clin Nutr 2002;76:911-922. Abstract

Godek SF, Bartolozzi AR, Godek JJ. Sweat rate and fluid turnover in American football players compared with runners in a hot and humid environment. Br J Sports Med 2005;39:205-211. Abstract

Havel PJ. Dietary fructose: implications for dysregulation of energy homeostasis and lipid/carbohydrate metabolism. Nutr Rev 2005;63:133-157. Abstract

Kuehn BM. Experts charge new US dietary guidelines pose daunting challenge for the public. JAMA 2005;293:918-920. Abstract

Teff KL, Elliott SS, Tschop M, et al. Dietary fructose reduces circulating insulin and leptin, attenuates postprandial suppression of ghrelin, and increases triglycerides in women. J Clin Endocrin Metab 2004;89:2963-2972. Abstract

ABOUT THE AUTHOR



Stan Reents, PharmD, is a former healthcare professional. He is a member of the American College of Lifestyle Medicine (ACLM) and the American College of Sports Medicine (ACSM). He holds current certifications from ACSM (Health & Fitness Specialist), ACE (Health Coach) and has been certified as a tennis coach by USTA. He is the author of Sport and Exercise Pharmacology (published by Human Kinetics) and has written for Runner's World magazine, Senior Softball USA, Training and Conditioning, and other fitness publications.




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