Training on Empty: Good or Bad?
Q. 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?
A. That sounds logical, I know, but it's bad advice for two basic reasons. The first is simply common sense: You will feel more like training if you eat a small snack beforehand. It's important to enjoy your training, because you're not likely to keep doing an activity that you find unpleasant. I usually have a cup of instant coffee, made with one-third water and two-thirds skim milk, and a teaspoon of canola oil (to slow absorption), and a Tiger's Milk energy bar about 30 minutes before my workout. If you'd prefer not to drink coffee and don't like energy bars, a glass of skim milk and an apple would be fine. Avoid concentrated sugars which cause a spike in your blood sugar a candy bar or honey are no-nos or eating so much that you feel full and uncomfortable. Eat something small in volume and easily digested; that's why I like a Tiger's Milk bar. I eat my main meal as soon as possible after training. I'll explain why a little later.
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.
Most of the energy for a training session, weights or aerobics, come from the glycogen stored in your muscles. The glycogen comes from what you have eaten over the last several days, not your last meal. 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. As Lawrence E. Lamb, M.D., explained some time ago in The Health Letter, muscle glycogen has to be used by your muscles for energy; it can't get out of the muscles to raise your blood sugar. So where does the glucose for your brain come from?
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, according to Dr. Lamb, 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.
As you probably know, extra calories from any source, carbohydrate, protein or fat, are stored as fat. "The catch," says Dr. Lamb, "is that this is a one-way street." Fat cannot be used to form glucose. 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.
Dr. Lamb summed it up like 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 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.
To the best of my knowledge, Dr. Lamb's comments are still state-of-the-art. I have yet to hear any authoritative opinion to the contrary. Until I do, I plan to continue eating a pre-workout snack..
I promised to tell you why I eat a full meal shortly after training. 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. As explained on our products page, my favorite post-workout meal is our High Protein Oatmeal. I add mixed vegetables and fruit to the oatmeal and top with skim milk or a multigrain beverage.
I've had many questions on this topic. I hope this clears up the confusion about eating a pre-workout snack.
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