Hungry or hypoglycemic? Not fueling your body can lead to low blood-sugar levels. Why hypoglycemia may occur in women who exercise too strenuously

You've just finished an intense workout that you swear squeezed out every last bit of energy you had. You're thinking the worst is over, but before you know it you feel weak, drowsy, dizzy and confused. Looking in the mirror you notice how pale you are, and a headache sets in shortly thereafter. Your unsettling experience may be due to a condition called hypoglycemia, or low blood sugar. It occurs when blood levels of glucose, a sugar molecule that acts as a major energy source for the body, drop too low to fuel your activity. Though the most common cause of hypoglycemia is as a complication of diabetes, it can also occur in women who exercise too strenuously.

"Exercise demands fuel, and fuel comes from blood glucose and glycogen stores in the muscle and liver," explains Gail Frank, DrPH, RD, professor of nutrition at California State University, Long Beach. "Rapid, intense or long-term exercise places a big demand on blood glucose and uses it up until glycogen stores [from the liver] are diverted to [resupply] available blood glucose. The rapid demand creates a hypo or low blood level."

Blood Sugar & Your Body

What goes on in the body to create hypoglycemia? During digestion, the body breaks down carbohydrates into various sugar molecules. One of these molecules, glucose, is mainly controlled by the hormones insulin and glucagon that are released from the pancreas. When blood glucose levels are high after a meal--about 120 mg/dL, or milligrams of glucose per deciliter of blood--glucose is absorbed directly into the bloodstream. The liver accepts extra sugar and stores it in the form of glycogen. Beta cells in the pancreas release insulin, which acts as a key to unlock the body's cells and allow glucose in. This, in turn, lowers the blood-sugar level to the normal range of about 60 mg/dL. If the pancreas releases too much insulin, however, even more glucose enters your cells and your liver can't release glucose into your bloodstream. The result is low blood sugar, defined as a level below 45 mg/dL.

A common cause of hypoglycemia after exercising is not eating enough beforehand. Since many symptoms of hypoglycemia are similar to the feeling of hunger, some women confuse being hypoglycemic with being hungry.

"Low blood sugar does occur when an individual goes for a long time without eating," says Frank. "But the term 'hypoglycemic' should be used only after he or she is tested by appropriate health-care professionals. What's important to know is whether the blood sugar varies within a normal range. If an individual's body works normally, then blood sugar normally goes up and down and insulin helps keep it in check. Normal fluctuation means you don't have a severely low level where you're really, really weak at times. If blood sugar spikes really high and then falls really low outside the normal range, you're then usually clinically diagnosed as hypoglycemic."

In someone without diabetes, a doctor will test for three things to check for hypoglycemia. The first is its symptoms, which can include behavior changes such as irritability and moodiness, seizures, loss of consciousness, visual disturbances such as double and blurred vision, and an increase in heart rate and blood pressure. Your blood-glucose levels will be measured through a blood sample while you're experiencing symptoms. If you don't exhibit signs and symptoms of hypoglycemia in your initial visit, you may be asked to fast overnight to cause hypoglycemic symptoms and allow your physician to make a diagnosis. To finish off, you'll take a dosage of sugar to see if the symptoms are relieved. Your doctor should also check you for health conditions such as diabetes and obtain a medication history.

Keeping Your Levels Up

For women who are hypoglycemic due to intense exercise, not eating enough before training and/or having no stored glycogen, Frank recommends following a nutrition plan that combines carbohydrates, adequate fluid and a protein/starchy snack with a little fat a few hours before your workout. "This type of snack would allow for a slower metabolism and sustain the glucose flow at a slower rate compared to juice or a candy bar, which would bring about an immediate demand on insulin to lower the blood sugar and create an even greater dip in blood sugar when the individual begins to exercise," she explains.

Although the average American's daily food intake is usually broken down into three meals, a fitness diet--where you eat 4-6 times a day--is more suitable. When blood-sugar levels drop due to not eating for a long time and/or too much exercise, alpha cells in the pancreas release glucagon. Glucagon signals the liver to release stored glycogen and change it back to glucose, raising blood-sugar levels to the normal range. But rigorous training requires an adequate fuel supply in the body, so when you don't eat before training or you just don't eat enough, the result can be hypoglycemia. Obviously, this can affect your workout.