updated 12/24/2003 7:05:44 PM ET 2003-12-25T00:05:44

A jolt of sugar can give an energy boost to people afflicted with a rare genetic disorder that causes them to tire after just a few minutes of exercise, a study found.

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An extra-sugary soda 30 to 40 minutes before a workout helped people with McArdle’s disease, a painful and sometimes dangerous illness in which a missing enzyme keeps muscles from using the stored sugar called glycogen.

In people with the disease, walking a block or two can cause cramps and even kill muscle tissue. Severe muscle damage can lead to kidney failure.

This is the first treatment ever for the disease, Drs. Ronald G. Haller and John Vissing reported in Thursday’s New England Journal of Medicine.

However, Dr. Alfred E. Slonim, director of the metabolism division at North Shore University Hospital in Manhasset, N.Y., warned that the sugary snacks could lead to obesity and diabetes. “I think it’s a bit of a dangerous paper,” he said.

The number of Americans with McArdle’s disease has been estimated at 2,900, or one in 100,000. But that estimate may be low, said Haller, whose study is in Thursday’s New England Journal of Medicine.

“Patients can go their whole lives undiagnosed,” said Haller, of the University of Texas Southwestern Medical Center and the Institute of Exercise and Environmental Medicine at Presbyterian Hospital in Dallas.

That is because at rest — for instance, sitting in a doctor’s office — patients look normal and have normal strength. “It’s just with activity that they run out of gas so readily,” Haller said.
Doctors have known for decades that intravenous glucose could help patients in the first minutes of exercise by giving them sugar in a form their bodies can use immediately.

Haller and Vissing, of the Copenhagen Muscle Research Center at National University Hospital in Denmark, tested the effects of a caffeine-free soft drink with 75 grams of sugar, almost double the amount in a 12-ounce Coke.

They had each of 12 patients ride a stationary bicycle for 15 minutes — once without any treatment, once 30 to 40 minutes after drinking the sugar-laden drink, and once after an artificially sweetened version.

To avoid cramps and possible injury, the doctors had patients slow down a bit if they became tired.

The patients said they could not tell which soda was which. Their bodies could, though. After the sugar-free drink, they became exhausted as quickly as usual. But after the high-sugar drink, their heart rates stayed lower and they felt less tired.

“Other sources of simple carbohydrates — candy bars, peanut butter-and-jelly sandwiches, orange juice and so on — are going to be effective as well,” Haller said.

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