Working Out on an Empty Stomach

Is training in the morning on an empty stomach more effective for burning fat?

Some well-known bodybuilding gurus recommend doing high-intensity aerobics in the morning on an empty stomach to burn fat. Is this supported by scientific fact, or is it bad advice ?

The main reason for a pre-workout snack, however, is to supply your brain with the energy it requires to function properly and to avoid cannibalizing your muscles.

All the different tissues of the body, including your muscles, use glucose, blood sugar, for energy. Your brain, however, relies on glucose for energy almost exclusively. If your blood glucose level falls, the brain cannot function properly. The result is usually inability to concentrate, lethargy and confusion, but in extreme circumstances can be blurred vision, shock, and even death. For this reason, the body is programmed to maintain your blood glucose level no matter what the cost. When you understand the mechanism by which this is accomplished, you’ll know why you should eat a small snack before you exercise.

It takes a day or two to restore the glycogen to depleted muscles. About 200 grams of glycogen can be stored in your muscles. Muscle glycogen, however, is no help to your brain.

First, it comes from the glucose contained in your circulating blood. This, however, is only about 20 grams and doesn’t last long. Next, it comes from the breakdown of glycogen to glucose in the liver; that’s about 70 grams. The glucose in your circulating blood and that stored in your liver, is enough to tide your brain over during the night, but that’s about it. When you get up in the morning the body must look elsewhere to supply glucose to your brain. Unfortunately, if you don’t eat, the source of supply is body protein, not the fat stored on your body.

Under normal circumstances, body fat can’t supply the needs of the brain. (After about two days of starvation body fat can provide energy to the brain, but that’s clearly not acceptable for our purposes.)

After blood glucose and liver glycogen are used up, the body turns not to fat tissue, but to protein to maintain the blood glucose level. The mechanism is called gluconeogenesis, the manufacture of new glucose. Your liver does the job. It strips the nitrogen from body protein to form glucose. In other words, protein from skeletal muscles and other body structures is used to maintain your blood glucose level.

Summing up this: “In the morning, after an overnight fast, your body has already switched to converting amino acids to glucose. That is one reason why some carbohydrate is needed to support your blood sugar level early in the morning is important. That can help conserve the cell protein, such as found in your muscles.”

So, training in the morning on empty, without eating, is a bad idea. The result is exactly the opposite of that desired. Rather than encourage the burning of fat, if forces your body to burn hard-earned muscle. The proper thing to do in the morning is to nourish yourself with the right dose of vitamins instead and here is a good list that HealthTrends put up.

Glycogen replacement is more than twice as great if you eat soon after exercising than if you wait two hours. It’s important to take advantage of that window of opportunity to replenish the glycogen stored in your muscles. Otherwise, the calories consumed may be deposited as fat.