If you are going to exercise at a relaxed pace for a few hours, you rarely need to eat or drink unless you feel hungry or thirsty. However, if you are going to compete in sports or exercise intensely for more than 70 minutes, you should take sugar just before you start and while you exercise.
The limiting factor to how fast you can move your muscles is the time that it takes to move oxygen into muscles. During exercise, your muscles use primarily sugar and fat for energy, and to a lesser degree, protein. Sugar requires less oxygen than fat or protein do, so you can move faster when your muscles burn mostly sugar.
You Have a Limited Amount of Sugar Stored in Your Body
Even skinny people have a virtually unlimited amount of fat stored in their bodies. However, they have only a very limited amount of sugar, stored in their muscles and liver. Even fit athletes have only enough sugar stored in their bodies to last for 70 minutes of intense exercise. When they run out of this stored sugar, they have to slow down. When you are exercising at low intensity, you burn a greater percentage of fat and therefore can keep on going for three or more hours without taking additional sugar.
There is only enough sugar in your bloodstream to last three minutes at rest. To maintain blood sugar levels, your liver constantly releases sugar into your bloodstream, but your liver holds only enough sugar to last about twelve hours at rest and for up to 70 minutes during intense exercise. When muscles run out of their stored sugar supply, it hurts to exercise and the muscles become difficult to control.
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. The muscles trained on sugar have no loss in the amount of stored sugar or the ability to convert food to energy.
You Should Not Carbohydrate Load
In 1939, studies showed that the more sugar an athlete can store in his muscles, the faster he could exercise over distance. As a result, many athletes adopted a training regimen called Carbohydrate Loading. Knowledgeable athletes do not do that any more.
The theory of Carbohydrate Loading was that you first empty muscles of their stored sugar by exercising close to exhaustion seven days before an endurance competition. This was supposed to help muscles to store more sugar when they fill up again with sugar. You kept the muscles low in sugar by restricting carbohydrates for four days, and then ate a regular diet plus large amounts of extra carbohydrates for the last three days before competition. However, athletes do not do that any more because after muscles fill with a meager amount of sugar, all extra carbohydrates are immediately converted to fat to make you fatter and extra fat in your body just slows you down.
What to Eat before Competition
All recent research show 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 for three days before a competition.
Three or four hours before a competition requiring endurance, you should eat your regular meal, provided that you do not start a competition with a full stomach. You can eat or drink anything you want as long as you avoid simple sugars. Try oatmeal, eggs, fruit or anything else that you normally eat for breakfast.
Why You Avoid Simple Sugars
When you take in sugared drinks or sugar-added foods, your blood sugar can rise very high. This causes your pancreas to release huge amounts of insulin. When you start to exercise, your exercising muscles and the extra insulin in your bloodstream will pull sugar so fast out of the bloodstream that you can develop a low-blood sugar level and feel very weak and tired. The energy for your brain comes almost exclusively from the sugar in your bloodstream. When blood sugar levels drop, so do brain levels, and you feel tired and have difficulty coordinating your muscles. The time to take your sugar boost is JUST before you start, and during your long competition as needed.
Five to ten minutes before your competition or workout starts (no sooner!), take any source of sugar and caffeine that you like. Sweetened tea, a caffeinated soft drink or a chocolate bar will work. The caffeine speeds up the rate that sugar enters muscles.
Eating and Drinking During Intense Exercise
You can drink any fluid that contains sugar. Several recent papers show that the combination of two sugars, glucose and fructose, brings sugar into muscles much faster than taking either one alone. That is not a problem because sucrose is a regular fruit sugar made up of both fructose and glucose, so you get both sugars when you eat any fruit or drink any fruit juice.
There is great controversy whether anything else is better. Commercial sugared sports drinks that contain both glucose and fructose may be slightly more quickly absorbed than commercial sodas that may contain only glucose. However, the need to have both glucose and fructose is not significant unless you are competing in high-level events that last more than 70 minutes.
Endurance Events That Last Longer than Three Hours
In endurance events lasting longer than three hours, you also need protein, solid foods and salt. You can eat salted potato chips, a sandwich of your choice or anything else that you normally eat or that is convenient for your sport.
Don't Take Sugared Drinks When You Are Not Exercising
ALL sugared drinks should be consumed only during exercise or immediately after. When you are not contracting your muscles, your main drink should be water. Sugared drinks cause much higher blood sugar levels than sugar-added foods. When food enters your stomach, the pyloric sphincter at the end of your stomach closes and the stomach can squeeze only the soupy liquid into your intestines. Sugared liquids enter your intestines immediately while fruit can stay in your stomach for up to five hours. A high rise in blood sugar causes sugar to stick to the outer membranes of cells and destroys them. A high rise in blood sugar increases risk for obesity, diabetes and heart attacks.
It is usually safe to take sugared drinks while you exercise because blood sugar levels rarely rise too high during exercise or for an hour afterward. Contracting muscles do not require insulin to take up sugar and therefore draw sugar so rapidly from the bloodstream that there is no sharp rise in blood sugar. This protection lasts maximally for up to an hour after you finish exercising.