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Carbohydrate Loading DOES NOT Work
"Carbohydrate loading" the night before a big race can impair your performance and damage your health. More than 45 years ago, in the Journal of the American Medical Association (March 26, 1973;223(13):1511-1512), I reported the case of a marathon runner who had a heart attack after carbohydrate loading.  
 
The "carbohydrate loading" regimen was supposed to increase the amount of sugar stored in your muscles before a race or endurance competition (Acta Physiol Scand.,1967;71:140-150).  First proposed in 1939, the process took several days: a four-day depletion phase and a three-day loading phase.
• Seven days before a competition: Exercise for several hours to deplete your muscles of their stored sugar supply (glycogen).
• Six to four days before competition: Keep your muscles empty of sugar by severely restricting all carbohydrates (sugar, fruits, flour, bakery products, pasta and so forth)
• Three to one days before competition: Eat your regular meals with lots of extra carbohydrates including bakery products and pastas.
• The night before competition: Eat a huge high-carbohydrate meal of pasta and bakery products.
 
Why Carbohydrate Loading Doesn't Work
We now know that the theory behind carbohydrate loading was wrong because even if you are skinny, you have a tremendous amount of fat in your body but only a very limited amount of sugar stored in your liver and muscles. You have only enough stored sugar to last for 12 hours at rest and 50 minutes of intense exercise.  When you eat a lot of carbohydrates, a small amount of sugar (glycogen) is stored in your liver and muscles, and after your muscles and liver are filled, all of the rest of the sugar you take in is quickly converted into a type of fat called triglycerides.  When you load up on refined carbohydrates such as bakery products, pastas and potatoes before a competition, you just become fatter. All the extra fat that forms will cause you to carry extra weight and slow you down during your race. If you already store too much fat, this overloading can load your liver with fat to make you diabetic or even suffer a heart attack. If you already have blocked arteries leading to your heart, you can kill yourself by loading with sugar or flour for just one meal.
 
A review of 88 studies showed that eating carbohydrates during competitions lasting longer than 70 minutes will prolong your endurance far more than anything you eat before a competition. The longer the event, the greater the benefit of eating during competitions (Sports Medicine (Auckland, NZ), September 2011;41(9):773-92).
 
How Muscles Use Carbohydrates for Energy
Carbohydrates are single sugars, double sugars, chains of sugars called starch, and thousands of sugars bound together called fiber. You cannot absorb any carbohydrates until they are broken down into single sugars.  Your muscles use primarily sugar and fat for energy, but sugar is the primary energy source for speed and endurance.   The limiting factor to how fast you can move is the time it takes to bring oxygen into muscles. During intense exercise, if oxygen is not transported to muscle cells fast enough, you have to slow down because you run low on an energy source called ATP.  However, fat cannot generate ATP as fast as sugar can, so the harder you exercise, the greater the percentage of sugar that your muscles need as their source of energy.  When you run low on sugar to power your muscles, you run low on ATP and you have to slow down (Clin Physiol, 1981:1:27-42). Anything that will help you to store more sugar in your muscles will also help you to move faster for a longer period of time. 
 
How Endurance Athletes Can Maximize Sugar in Muscles
Research in the 1980s led to replacement of the old seven-day carbohydrate-loading regimen with a new three-day training program that eliminated both depletion and loading phases. All recent research on the subject shows that conditioned athletes can store the maximum amount of sugar in their muscles just by continuing to eat their regular diet and cutting back on the amount of training they do for three days before a competition.
 
The day before the race: Do a very short, extremely high-intensity workout (such as a few minutes of sprinting) and then eat some extra food during the next 24 hours. This results in a 90 percent increase in muscle sugar storage. Avoid sugared drinks and sugar-added foods as these can cause high blood sugar levels that can make you feel sick.
 
The pre-race meal: You can eat anything you want as long as it:
• can pass from your stomach before you start the race, and
• is not full of sugar.
Most athletes take their pre-race meal three to four hours before they compete. The meal should contain some protein in addition to carbohydrates, but avoid sugar-added drinks or foods. A pre-race meal could include eggs, oatmeal or other whole-grain cereals, oranges or other fruits, bagels and so forth.
 
Eating and drinking just before your race: The best time to take sugar to help you prolong your intense exercise is 30 minutes or less before you start. You can even eat chocolate because it contains both sugar and caffeine. Taking a sugar load more than 30 minutes before competition can cause a high rise in blood sugar which will cause your pancreas to release large amounts of insulin. Then you start your race with high insulin levels that, combined with your muscles suddenly pulling large amounts of sugar from your bloodstream, can cause low blood sugar levels that can make you feel exhausted even though you have just started your race. Researchers in Scotland showed that taking a sugared drink 30 minutes before exercise allowed the subjects to exercise at 90 percent of their maximum capacity for 12 percent longer than when they took the same sugared drink two hours before exercise (International Journal of Sport Nutrition and Exercise Metabolism, November 2013). The researchers showed that taking sugar two hours before exercise does not help you to sustain intense exercise any longer than taking nothing at all. 
 
Eating and drinking during competition: Athletes start to run out of the sugar stored in their muscles after 50 minutes of intense competition, so you need to take sugar during endurance sport competitions that last longer than 50 minutes (Medicine & Science in Sports & Exercise, July 2010). However, you can exercise at a relaxed pace for more than three hours without needing sugar. Caffeine can increase the rate that sugar enters muscles by more than 26 percent (Journal of Applied Physiology, June 2006), so most athletes take their sugared dinks and foods with some source of caffeine. Ordinary beverages containing both sugar and caffeine are fine; there is no need for special sports energy drinks or gels. See Caffeine Improves Endurance. Caution: on very rare occasions, caffeine can cause some susceptible people to develop irregular heartbeats.
 
For endurance events lasting more than three hours:  In endurance events lasting longer than three hours, you need carbohydrates, protein, fluid and salt. In addition to rich sources of sugar (sugared drinks, fruit, chocolate bars). You can eat heavily-salted potato chips, French fries, any sandwich of your choice or anything else that you normally eat, as long as it does not make your stomach feel uncomfortable.
 
NO Sugared Drinks When You Are Not Exercising Intensely
You should take sugared drinks only during vigorous exercise and for up to an hour after you finish. Contracting muscles remove sugar from the bloodstream rapidly without needing much insulin. Taking sugared drinks when you are not exercising causes higher rises in blood sugar that increase risk for diabetes and cell damage. More on Sugared Drinks
 
Eat Carbohydrates and Protein to Recover Faster
You will recover faster by eating a high carbohydrate, high-protein meal within a half hour after finishing a race or a grueling workout (Journal of Applied Physiology, May 2009).  Taking the same high-protein-and-carbohydrate meal before a race or intense workout does not hasten recovery. Carbohydrates in the post-race meal cause a rise in blood sugar that causes the pancreas to release insulin, which drives the protein building blocks (amino acids) in the meal into muscle cells to hasten healing. Muscles are extraordinarily sensitive to insulin during exercise and for up to an hour after finishing exercise, so the fastest way to recover from intense workouts and races is to eat a protein- and carbohydrate-rich meal within an hour after you finish. You can use either plant or animal sources of protein; both contain all of the essential amino acids necessary for cell growth. Foods for Recovery
Minerals
The only mineral that you need during long endurance events is salt. The food you eat will supply all of the potassium, calcium, and magnesium you need. You should eat salty foods during and after you finish long rides and races, particularly on hot days when you sweat a lot. More on Salt
 
No Advantage to Restricting Sugar During Intense Training
The question had been asked whether restricting sugar during training could enhance performance by teaching the muscles to get along with less sugar. The enzymes used to convert sugar and fat to energy function just as well when sugar is taken continuously during exercise. A study from Copenhagen, Denmark shows that taking sugar while you exercise increases the amount of training you can do, and does not lessen the benefits of your increased training (Journal of Applied Physiology, June 2009). In this study, men trained one leg while ingesting a 6 percent sugar drink and the other leg while taking an artificially sweetened (sugarless) drink, two hours a day, on alternate days, five days a week. The legs trained with sugar had 14 percent more power and a 30 percent greater time to exhaustion. The muscles trained on sugar have no loss in the amount of stored sugar or the ability to convert food to energy.
January 27th, 2019
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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