Many doctors are skeptical about a condition called reactive or “functional” hypoglycemia (low blood sugar a few hours after eating a high-carb meal). Perhaps that is because there were several popular books on this topic in the 1970s. Some physicians characterized people who thought they had hypoglycemia as neurotic (JAMA, Sept. 22, 1975).

Forty years later, research is catching up with the idea that what you eat has a profound impact on your physiology. Scientists are paying attention to the glycemic index. This is a way of measuring how quickly a food makes blood sugar (glucose) rise. If blood sugar soars, insulin follows. When insulin is effective at clearing blood sugar, glucose may drop precipitously. The result can be symptoms such as shakiness, sweating, weakness, anxiety, rapid pulse, confusion and hunger or a craving for sweets.

One reader recently reported his experience: “I read about postprandial reactive hypoglycemia (PRH) in your column. It surprises me that I had never heard of it before because I have been a volunteer EMT on the emergency squad for the past five years.

“Not only that, but I have PVCs (premature ventricular contractions of the heart) that seem to kick up after I have had a high-carb supper like waffles or pancakes. Years ago, I had to quit eating pancakes for breakfast on Saturday, because often after such a breakfast, I’d go out and do yard work and get so weak midmorning I could hardly stand up. I’d be craving sweets like there would be no tomorrow. A piece of toast and jelly would bring me around.

“Recently, I asked my cardiologist about any possible connection between pancakes with syrup and palpitations. He said, ‘No way.’

“The next time this happens, I need to have my wife drive me down to the emergency squad, where I can get my hands on a glucometer and check my blood sugar for a dip. That might be the only way to conclusively prove if PRH is really the cause.

“As an EMT, I have run into several instances of sudden, unexplained weakness in patients without diabetes, and I did not think to run a BGL (blood glucose level) check. From now on, I will probably check BGL in cases of unexplained changes in weakness or heart-rhythm anomalies following a meal.”

Although many others may be able to relate to the restorative properties of toast and jelly (a snack that would boost blood sugar very quickly), preventing such episodes calls for avoiding foods with a high glycemic index.

Another reader almost passed out after a high-carb meal. She had to call a family member to drive her home.

She suggests that others with reactive hypoglycemia try to keep blood sugar in a normal range: “I always carry nuts and peanut-butter crackers in my purse. I eat a high-protein snack every two to three hours. It takes a while to fully recover from symptoms of low blood sugar, such as headache, nausea and fatigue.”

People who are susceptible to this problem need to be cautious about foods with a high glycemic index. That includes Christmas cookies, fruitcake, traditional holiday breads like stollen or panettone and brunch foods like French toast, pancakes and waffles with syrup. Instead, the best approach is likely to be a low glycemic index diet rich in protein, fat and low-carb veggies.

Joe Graedon is a pharmacologist. Teresa Graedon holds a doctorate in medical anthropology and is a nutrition expert. Their syndicated radio show can be heard on public radio. In their column, Joe and Teresa Graedon answer letters from readers. Write to them in care of this newspaper or email them via their Web site: