Sugar levels: the harder you run, the harder they fall.

? I'm a 63-year-old male. I've been running for 22 years and run about five miles six days a week at 10:00 pace. I have a strong family history of diabetes. The results of my glucose tolerance test were a low of 60 and a high of 99. [Editor's note: in a "glucose tolerance test," a fasting level of glucose (simple sugar) in the blood is obtained, then various levels two or more hours after drinking a glucose solution, to determine whether the glucose level in the blood remains abnormally high after sugar intake.]

For years, there would be days I'd get weak-kneed after a mile and a half, and then shake it off a mile or so later and feel fine. Bagels, sports drinks or energy bars before runs often give me that feeling during the run--even if I consume them several hours beforehand. But black coffee and a glass of orange juice before a run never seem to cause me any trouble. My doctor says it is mild hypoglycemia (low blood sugar). Since he's not a runner, what are the implications of this? Is it common? Do you think I'll become diabetic?

Howard Leftis, Bloomfield, MI

The results of the glucose test are in the normal range and if you keep your lifestyle and fitness levels as they are now, your risk of developing diabetes is low. Your symptoms suggest reactive hypoglycemia, which usually occurs after heavy refined carbohydrate intake; why the orange juice doesn't cause it along with the other carbohydrate-rich foods, I don't know.

William M. Simpson, Jr., MD, Charleston, SC

Whenever we take in food, it is converted to simple sugar so it can be used by our brain and muscles. Insulin is released from the pancreas in response to this influx of glucose to allow it to pass out of the bloodstream and into the muscles. In some people, the insulin lowers the glucose level too vigorously and they become light-headed, weak or nauseated. This is what we mean by reactive hypoglycemia. Exercise can often cause dips in glucose that may produce these symptoms. Runners already with this condition may experience profound fatigue during exercise.

The lab data suggests that you are not diabetic. But type!! diabetes can sometimes develop later on in people with similar situations as yours, so it's best to obtain a fasting blood sugar level each year.

Reactive hypoglycemia is more of a nuisance than a serious condition. It's as common in runners as in the general population, and the treatment is essentially dietary. Eating four or five small meals a day is better than three large ones as it helps maintain even glucose levels throughout the day. Eat snacks and small meals with a low glycemic index. The glycemic index quantifies how readily the body converts a certain food into glucose. The idea is to try and avoid triggering the massive insulin response. Oranges have a lower glycemic index than bagels, whose sugars enter the blood stream more rapidly, so orange juice may not trigger the symptoms as severely or as often. For this reason, other fruits would make good prerun meals as well. It's also possible that the caffeine in your coffee is improving your ability to convert fat to glucose. Visit www.mendosa.com/common_foods.htm for a more complete list of foods and their glycemic indices.

Douglas Johnson, MD, FAAFP, Morganfield, KY

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It's a Start

In March, McDonald's announced it will phase out supersizing by the end of the year. The extra-large 7-ounce French fries and 42-ounce soft drinks will be downsized to 6.2 and 32 ounces, respectively.

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