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The Potassium Deficiency Myth

Sports drink promoters have convinced many athletes that they need special drinks to replace potassium during exercise. A recent study of female soccer players confirms that this is a myth (International Journal of Sports Medicine, June 2009). When body levels of potassium are low, the kidneys and sweat glands conserve potassium so effectively that potassium deficiency rarely occurs.

Tiredness in healthy athletes can have many causes, but low potassium is not one of them. Many years ago, Dave Costill of Ball State University tried to create potassium deficiency in healthy national champion runners. He couldn't do it because potassium is found in all foods except refined sugar, and his athletes would not stay on a diet that consisted only of hard candy. Even with prolonged exercise in very hot weather, potassium needs can be met by eating virtually any food.

Potassium deficiency CAN be caused by certain drugs, such as diuretics or corticosteroids, or by severe diarrhea or repeated vomiting. One of the best female long-distance runners in the country came to me to find a cause for her sudden drop in performance. All tests I ordered were normal except for a low blood level of potassium. I knew that hard exercise does not cause potassium deficiency and that the most common cause of potassium deficiency is vomiting, but she repeatedly denied doing this. I then requested that she collect her urine for one day and the laboratory reported that it contained three times as much potassium as normal. This proved that she was bulemic. To control her weight, she was sticking her finger down her throat to makie herself throw up. After she was able to accept the diagnosis, she got help, stopped vomiting and went on to win several national long distance running titles.

With vomiting, you throw up the stomach's acid (hydrogen) and the blood becomes alkaline. This causes the kidneys to retain hydrogen and consequently lose huge amounts of potassium in the urine. In both athletes and non-athletes, the most common cause of low potassium blood levels and high potassium urine levels is vomiting.

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Dear Dr. Mirkin: Will fasting before a race give me more endurance?

No! Fasting weakens and tires you. How long you can exercise a muscle depends on how much sugar, called glycogen, you can store in that muscle and how long you can keep it there. When a muscle runs out of its stored glycogen, it slows down because it requires more oxygen to burn more fat. It also accumulates more lactic acid to become acidic which causes a burning pain, and it becomes more difficult to coordinate.

Every time you move a muscle, some of the stored glycogen is used up. Every time you eat, some of the food can be stored as glycogen in that muscle. When you go for more than an hour without eating, you use up glycogen without replacing it. If you don't eat before you compete, you start with reduced stores of glycogen in your muscles and you will not be able to compete at your best.

It is nonsensical to claim that fasting increases endurance by causing muscles to burn more fat and less glycogen so muscles can retain their stored glycogen longer. When you start with less glycogen, you still use it up faster and run out of fuel earlier. You can increase endurance by cutting back on exercise four days before your competition and eating as much or more than usual. Eat one to three hours before competing. If your event lasts more than an hour, take fluid, sugar and protein (whole grain bars, sugared drinks, etc.) during your event.

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Dear Dr. Mirkin: Should I take antioxidants pills such as vitamins A, C and E?

Probably not. Several recent studies have shown that taking antioxidants pills can reduce the health benefits of exercise in humans (Proceedings of the National Academy of Sciences, May 12, 2009). Now a study from Australia shows that they may also contribute to diabetes (Cell Metabolism, October 7, 2009). The authors showed that low levels of oxidants ("reactive oxygen species" or ROS) prevent diabetes in mice by improving their ability to respond to insulin. Normal mice develop diabetes when fed a high fat diet over many months. Mice bred so they could not eliminate ROS didn't develop insulin resistance when fed a high-fat diet. However, when these mice were given antioxidants, which clear ROS from their blood, their blood sugar levels rose and they developed diabetes. The authors showed that ROS in muscles increase the body's ability to respond to insulin to help lower blood sugar levels.

When you exercise, your muscles convert food to energy by moving electrons from one molecule to another. Eventually you end up with extra electrons. If they attach to hydrogen, they are converted to water which is harmless. However, if the electrons attach to oxygen, they become reactive oxygen species (ROS) that can damage cells, but they also stimulate insulin receptors on cells to respond to insulin.

Contracting muscles markedly increase their conversion of food to energy, so they produce extra electrons to make more ROS. However, exercising muscles produce far more antioxidants to rid themselves of the extra ROS so they do this much more rapidly than muscles of non-exercisers.

This new study shows how antioxidant pills can reduce ROS enough to prevent insulin receptors from being able to respond to insulin, which would increase risk for diabetes. The study reinforces recommendations I have given for years: exercise every day, and get the antioxidant vitamins and other nutrients your body needs from foods, not from pills. Eat a wide variety of foods including large amounts of fruits, vegetables, whole grains, beams, nuts and other seeds.

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Recipe of the Week:

Quick Moroccan Vegetable Stew

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June 22nd, 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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