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How to Eat When You Exercise

If you are going to exercise for more than an hour, you can increase your endurance by eating every 15 to 20 minutes. A feeling of general tiredness during exercise is usually caused by low levels of stored sugar in your liver, while a feeling of muscle fatigue is usually caused by low levels of stored muscle sugar.

Your brain gets more than 98 percent of its energy from sugar flowing to it in the bloodstream, but there is only enough sugar in your bloodstream to last for three minutes. Your liver must constantly release sugar from its cells into your bloodstream. However, there is only enough energy in your liver to last about 12 hours without replenishment.

Your muscles get their energy from many sources: sugar and fat stored in them, and sugar, fat or protein in the bloodstream. When your muscles run out of their stored sugar supply, they can hurt and feel tired. You can increase endurance by eating frequently, and you can eat whatever you like: nuts, fresh or dried fruits, chicken, sandwiches or anything else. The amount of sugar you get in sports drinks is not adequate to support strenuous exercise for long periods of time.

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Dear Dr. Mirkin: I feel tired all the time. Will iron pills help?

You should not take iron pills without a specific diagnosis. Several studies have shown that iron deficiency can be healthful. Before the bad LDL cholesterol can form plaques in arteries, it must be converted to oxidized LDL and iron causes this reaction. Lack of iron reduces your chances of forming plaques in your arteries and suffering heart attacks and strokes.

Less than 50 percent of the iron in your body is in your red blood cells. Most iron is in your iron reserves in your liver, spleen and other tissues. Your body needs iron to make red blood cells and if your body does not contain enough iron, you will become anemic, but you will not become anemic until you have depleted all your iron reserves. You can be iron deficient but not anemic when you have an adequate supply of red blood cells, but no iron reserves. Iron deficiency does not make you tired unless you are also anemic, but it can tire athletes exercising at their maximum.

Blood iron levels are parts of routine blood tests. If your blood iron levels are low and you are not anemic, you need a special test called ferritin to measure iron reserves. If your ferritin is low, your doctor will look for a source of bleeding such as heavy menstruation or through your intestinal tract. If no serious source is found, you need no treatment unless you are a highly competitive athlete.

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Hot pepper follow-up: In last week’s question about pepper cream, I noted that capsaicin is a very stable alkaloid that does not wash off your skin with soap. One reader sent this helpful suggestion: "We work in the food service industry and often deal with capsaicin. We have had a great deal of luck using lemon juice to remove the residual from our hands. You can use either a lemon wedge rubbed over the area or lemon juice from a bottle. Please give it a try and see if it works for you as well as it has worked for us." Thanks, Joann!

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Dear Dr. Mirkin: Why do I get goosebumps on my skin?

In prehistoric times, goose bumps may have helped humans frighten their enemies. Now they’re not much use. The hairs on your body lie close to your skin and have small muscles attached to them called arectores pilorum. When you feel cold or are frightened, these muscles pull on the hairs so they stand out almost perpendicular to your body, causing small bumps to appear. Hairs trap air between them in the same way that the fibers in a sweater trap air, helping to keep you warm. The arectores pilorum muscles also press against the oil glands located at the base of each hair shaft and squeeze oil onto the surface of the skin. The oil covers the skin's surface and helps to keep the skin warm by reducing evaporation of sweat from the skin's surface.

Many thousands of years ago, people had more body hair and fewer clothes. Contraction of arectores pilorum muscles caused hair to stand on end, making a man appear larger than he was. Today, our greatest adversaries are other people, and goose bumps may reveal that you are scared. Now most people hide their goosebumps with clothes.

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Two more healthful, tasty recipes with an Asian accent:

Seafood Stir Fry
Tofu Fried Rice

List of Diana's Healthful Recipes

June 27th, 2013
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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