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Sodas with HFCS and Caffeine May Be Best Drinks for Endurance

The limiting factor in endurance racing is the time that it takes to get enough oxygen into muscles to burn food for energy. Anything that reduces oxygen requirements allows you to race faster. Sugar stored in muscles, called glycogen, requires less oxygen than fat or protein. Anything that helps you keep sugar in muscles longer gives you greater endurance.

A study from Georgia State University shows that drinks that contain both glucose and fructose burn more carbohydrates than those containing only glucose, and allow cyclists to ride much faster over 60 miles (International Journal of Sport Nutrition and Exercise Metabolism, April 2010).

Most soft drinks are sweetened with high fructose corn syrup (HFCS). Both HFCS and conventional sugar (sucrose) contain a mixture of two sugars, glucose and fructose, in nearly the same concentrations: HFCS has 55 percent fructose/42 percent glucose, while sucrose is a 50/50 mixture. So the relative concentrations of glucose and fructose are not significant. However, the fructose in sucrose from cane or beet sugar is bound to glucose and must first be separated from it, so it is absorbed more slowly into the bloodstream. The manufacturing process for HFCS frees the fructose from glucose to makes it into a free, unbound form that is absorbed more rapidly into the bloodstream. This could cause a higher rise in blood sugar ((Pharmacology, Biochemistry and Behavior, March 18, 2010) and provide more sugar for muscles during exercise. We need to wait for more research to know if HFCS drinks improve endurance more those made with cane or beet sugar.

Caffeine increases endurance (Medicine & Science in Sports & Exercise, July 2010) by increasing absorption of sugar by muscles (Journal of Applied Physiology, June 2006). Those who took sugared drinks with caffeine were able to absorb and use 26 percent more of the ingested sugar than those who took the same drinks without caffeine.

On long rides, we drink colas for their sugar and caffeine. However, you should take sugared drinks only when you exercise and for up to an hour after you finish. Contracting muscles remove sugar from the bloodstream rapidly without needing much insulin. Taking sugared drinks when you are not exercising causes higher rises in blood sugar that increase risk for diabetes and cell damage.


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Dear Dr. Mirkin: What are the signs of heat stroke?

As your temperature starts to rise, your muscles burn and feel like a hot poker is pressed against them. If your temperature rises further, you become short of breath and the air you breathe feels like it is coming from a hot furnace. Stop exercising and cool off because if your temperature rises further, you will develop brain symptoms such as dizziness, headache, blurred vision or ringing in your ears. If you press on, you can pass out and die. The treatment for a person who collapses from heat stroke is immediate immersion in cold water (Medicine and Science in Sports and Exercise, July 2010).

Heat stroke, when the body temperature rises so high that it cooks the brain, is the most common cause of death during hot weather sports events. Those most likely to suffer heat stroke are overweight, have arteriosclerosis or are not in good shape. Taking stimulants such as amphetamines, caffeine or ecstacy increases risk of heat stroke.


Dear Dr. Mirkin: Does eating eggs damage arteries?

Eating three eggs at one time or taking two eggs per day for six weeks does not constrict arteries in people with high cholesterol (Nutrition Journal, July 2010). Researchers use a test for endothelial dysfunction to predict which foods are likely to increase risk for arteriosclerosis. The inner lining of arteries releases a hormone called endothelin that constricts arteries to increase risk for arteriosclerosis, heart attacks, and diabetes. This is called endothelial dysfunction. The inner lining of arteries can also release nitric oxide to open arteries and help to reverse arteriosclerosis.

In the same study, people who ate egg subsitutes (with no cholesterol or saturated fat) daily for six weeks had even less artery constriction than those who ate the whole eggs. The authors do not explain this finding.

Multiple studies show little, if any, evidence that eating eggs is associated with increased risk for heart attacks or death. The main concern about eggs is their extremely high concentration of cholesterol. However, most research on cholesterol in foods has failed to show that dietary cholesterol increases heart attack risk. Large population studies do show increased risk for heart attacks in people who eat mammal meat, but not those who eat poultry. Those who eat fish and plants have reduced heart attack risk. Journal references


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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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