Digestion involves a complicated series of events that provide the necessary fuel and nutrients for proper body function. While eating before exercising might seem like a good idea, it can actually hamper your workout due to the stomach upset you may experience. Digestion requires several hours to fully metabolize foods. Indeed, research published in 2010 in the "Journal of Physiology" found that exercising in a fasted state helps the muscles adapt better to exercise.
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How Digestion Works
Before you exercise, your body undergoes a five-step process to digest any foods you have eaten. Digestion begins in the mouth, where enzymes begin breaking down foods. The food will then move through your system to the stomach. The stomach prepares food for absorption by the intestines; it will not absorb most of the food you've eaten, according to the textbook "Principles of Anatomy and Physiology." Nutrient and water absorption occur primarily in the small and large intestines. Indigestible materials are then eliminated from the body. Food will leave your stomach about two to six hours after you eat it.
Digestion's Impact on Your Exercise
The types of food you eat can influence how long digestion takes and what impact it has on your exercise. Generally, your body can easily digest simple carbohydrates like fruits. Part of the reason lies in their chemical structure. Digestion, after all, is basically a process of chemical reactions. Proteins, on the other hand, are chemically more complex. These foods will take longer to digest. Because they stay in your stomach longer, you may experience nausea from exercising too soon after eating high protein foods.
Availability of Sugar and the Glycemic Index
In the gastrointestinal system, the pancreas and liver play vital roles in metabolism of the foods you eat. The pancreas will help control your blood sugar. The glycemic index measures how quickly sugar enters your bloodstream. The higher the GI, the more quickly this process occurs. In terms of exercise, the availability of sugar will help fuel your muscles, particularly during intense exercise. During vigorous exercise, the body relies more on carbohydrates for energy.
Why You Eat Two Hours Before Exercising
You should wait at least two hours after eating before exercising. When you begin to work out, your body switches gears and goes into fight-or-flight mode. Digestion slows as your body directs blood flow to your muscles. Likewise, the body directs energy to the muscles. The body has evolved so that digestion is a passive process, not the body's primary function during activity. If you wait to exercise, you can take advantage of the rise in blood sugar and the availability of energy for a more effective workout.