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Should You Train on Depleted Glycogen Stores?

An article from Australia shows that novice exercisers who train after skipping breakfast have higher muscle levels of glycogen (stored sugar) than those who train after eating breakfast (Journal of Science and Medicine in Sport, May 2010). When you run out of stored muscle sugar, you have to slow down, so having more sugar stored in a muscle should help you exercise longer. The faster you exercise, the greater the percentage of sugar that you use for energy. However, starting workouts with depleted stores of glycogen will not benefit competitive athletes who train for many hours each day, because restricting carbohydrates will cause them to tire earlier and thus do less work.

In another study, researchers asked competitive athletes to train either on a high or low-carbohydrate diet (Journal of Applied Physiology, November 2008). Those training on the low carbohydrate diet had much greater gains in stored muscle sugar and ability to use fat for energy during cycling, although they couldn't train as intensely as the high-carbohydrate group in the first few weeks. However, during the last week there were no differences in training. Both groups improved their one-hour time-trial performances by about 12 percent.

More recent data show that taking sugar during training sessions increases the amount of training an athlete can do without interfering with racing times (Journal of Applied Physiology, February 2009). At this time we do not have enough data to recommend restricting carbohydrates during training, or that it will increase endurance during competition.

CAVEAT! Eating foods or drinks that cause a high rise in blood sugar within an hour before a race will cause you to tire earlier. A high rise in blood sugar causes your pancreas to release huge amounts of insulin which causes you to use up your stored muscle sugar at a much faster rate. When you run out of stored muscle sugar, you have to slow down because it forces you to burn more fat which requires more oxygen. Getting oxygen into muscles is the limiting factor in how fast you can race. Researchers at the University of Hull in the United Kingdom showed that bicycle racers rode much faster 40 kilometer time trials 45 minutes after eating a low glycemic index (GI) pre-race meal than a high glycemic one (Journal of Science and Medicine in Sport/Sports Medicine Australia, January 2010). The low GI meal led to an increase in the availability of carbohydrates and a greater carbohydrate oxidation throughout the time trial.

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Dear Dr. Mirkin: Should I start drinking alcohol to prevent a heart attack?

Nobody has shown that drinking alcohol prevents heart attacks. Moderate drinkers are less likely to suffer heart attacks than non-drinkers or those who drink to excess, but they are also more likely to avoid other unhealthful habits. They tend to have a higher social status, exercise more, suffer less depression and enjoy superior health overall compared to heavy drinkers or lifetime abstainers (European Journal of Clinical Nutrition, May 2010). They also weight less and have lower fasting triglycerides and blood sugar (meaning that they take in fewer calories), lower blood pressure, lower levels of the bad LDL cholesterol, higher levels of the good HDL cholesterol, and other factors associated with a lower risk of heart disease. So the health benefits that have been attributed to alcohol consumption may really be due to other healthful habits that accompany moderate alcohol consumption.

One in ten people who start to drink alcohol will drink to excess because they have inherited a gene for alcoholism. Drinking alcohol is not associated with a shortened lifespan until you exceed two drinks a day (a drink is defined as 12 ounces of beer, 5 ounces of wine, or 2/3rds of a shot glass).

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Dear Dr. Mirkin: Does sugar consumption affect blood pressure? Omitting one sugar-sweetened beverage per day for 18 months lowered high blood pressure in 800 people (Circulation, May 2010). No association was found between caffeine intake or diet beverage consumption and blood pressure. This study suggests that anyone concerned with high blood pressure should avoid all sugared beverages, including fruit juices, except during exercise.

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Recipe of the Week:

Summer Couscous

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June 21st, 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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