Carbohydrate Loading Just Doesn’t Work. Here’s Why.

July 16, 2015 Updated: July 17, 2015
FONT BFONT SText size
“Carbohydrate loading” the night before a big race can harm your performance and your health. More than forty years ago, I reported the case of a marathon runner who had a heart attack after carbohydrate loading in the Journal of the American Medical Association. A review of 88 studies shows 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).
 
Bill Summa, left, of New Mexico, Mike Bauer, center, and Tom Van Veen, right, both of Oregon, load up a dinner high in carbohydrates in Boston on April 16, 1989. The dinner is provided free of charge to all who will run in the 93rd Boston Marathon on Monday. (AP Photo/Julia Malakie)
Bill Summa, left, of New Mexico, Mike Bauer, center, and Tom Van Veen, right, both of Oregon, load up a dinner high in carbohydrates in Boston on April 16, 1989. The dinner is provided free of charge to all who will run in the 93rd Boston Marathon on Monday. (AP Photo/Julia Malakie)

How Did Carbohydrate Loading Get Started?

First proposed in 1939, the carbohydrate loading regimen was supposed to increase the amount of sugar stored in your muscles before a race or endurance competition. 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) * 3 to 1 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.

We now know that the theory was wrong because your muscles can only store a very limited amount of sugar and all extra carbohydrates are immediately stored as fat. 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 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.

How Carbohydrate Loading Can Harm

When you take in a lot of refined carbohydrates, your blood sugar rises. The first extra sugar is stored in your muscles and liver, but they only hold a meager amount. The liver then converts the extra blood sugar to a fat called triglycerides. A high rise in blood fat can cause clots, so much of the fat is immediately removed from your bloodstream. It is stored in fat cells, which makes you fatter, or in your liver. Fat in your liver drives blood sugar levels even higher. High blood sugar levels can cause inflammation, which can break plaques off from the inner lining of your arteries. This can block blood flow to the heart and cause a heart attack.

Participants run during the 2014 City To Surf race on August 10, 2014 in Sydney, Australia.  (Photo by Brendon Thorne/Getty Images)
Participants run during the 2014 City To Surf race on August 10, 2014 in Sydney, Australia. (Photo by Brendon Thorne/Getty Images)

You Only Need a Little Extra Sugar

The limiting factor to how fast you can move over distance is the time it takes for oxygen to get into muscles. Your muscles burn primarily sugar and fat for energy. You have an almost infinite amount of fat stored in your body, but only a small amount of sugar stored in your muscles and liver. Sugar requires less oxygen than fat does. When your muscles run out of sugar, your oxygen requirements increase and you have to slow down and even stop. 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. A rule of thumb is that you have enough sugar stored in your muscles to last during intense exercise for about 70 minutes. Athletes do not need to worry about extra sugar unless their competitive event lasts longer than 70 minutes. Realize that only a small amount of sugar can be stored in muscles. After your muscles and liver are filled with a small amount of sugar (glycogen), all the rest of the sugar is quickly converted into fat.

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 eliminates both depletion and loading. 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: The athlete does a very short, extremely high-intensity workout (such as a few minutes of sprinting) and then eats 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 the athlete 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, grapefruit and 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. Taking a sugar load more than 30 minutes before competition can cause a high rise in blood sugar which, in turn, causes 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. 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. You can even take chocolate because it contains both sugar and caffeine.
 

Eating and drinking during competition:

Athletes start to run out of their sugar stored in muscles after 70 minutes of intense competition, so you need to take sugar during endurance sports that last longer than 70 minutes. However, you can exercise at a relaxed pace for more than 3 hours without needing sugar. Caffeine can increase the rate that sugar enters muscles by more than 26 percent, so most athletes take their sugared drinks 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.