Carbohydrate Loading DOES NOT Work
“Carbohydrate loading” the night before a big ride or race can harm your performance and your health. More than 40 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 (JAMA, March 26, 1973;223(13):1511-1512).
A review of 88 studies shows that eating carbohydrates DURING rides 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, N.Z). September, 2011;41(9):773-92).
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)
Three days to one day 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.
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, so when your muscles run out of sugar, your oxygen requirements increase and you have to slow down and even stop (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. 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 the depletion phase. All recent research 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 no sugared 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.
Next week we’ll continue with what and how best to eat just before, during, and after an endurance event, what minerals you need during the event, and whether to restrict sugar during intense exercise.
Gabe Mirkin, M.D., is a sports medicine doctor and fitness guru. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin has run more than 40 marathons and is now a serious tandem bike rider with his wife, Diana. His website is http://drmirkin.com/. Click to read Gabe’s full bio.