Long Distance Running & Low Blood Sugar

Distance runners have distinct nutritional needs.
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One of the greatest fears for distance runners is "hitting the wall," or "bonking." These terms are used to describe the point during a run when an athlete's body experiences an extreme blood sugar drop, which leaves her feeling tired, weak, unable to think, and in some cases, results in total physical collapse. Not only is this a horrible feeling that can ruin any training session or race, it can also be dangerous. Take precautions with proper nutrition to stay healthy and avoid blood sugar crashes.


The medical term for bonking is hypoglycemia, a condition characterized by abnormally low blood glucose. Although it's commonly associated with diabetes, hypoglycemia isn't a disease, but an indication of a health problem. The body's preferred source of energy is glycogen, which is glucose formed from carbohydrates stored in the body's muscles and liver. Glycogen is released into the bloodstream to provide energy during activity. Most distance runners have around 2,000 to 2,200 calories worth of glycogen in their bodies, but once they run out, they're forced to rely on fat for energy. While fat is a rich source of fuel, your body converts it to energy at a much slower rate. This is when symptoms of hypoglycemia set in.

Dangers and Treatment

Left untreated, hypoglycemia is potentially dangerous. Your brain needs glucose to function, and without it, you may experience mental fog, confusion, extreme emotions or unconsciousness. If caught in time, the treatment for hypoglycemia is fairly simple for an otherwise healthy adult. Consuming simple sugars that are immediately processed and released to the blood stream, such as candy, juice or glucose tabs, will provide almost instant relief. If you're unable to take anything by mouth because the symptoms have gotten too severe, you may need a shot of glucagon or intravenous glucose. If you feel the symptoms of hypoglycemia, stop activity immediately and seek medical attention if necessary.

Fueling Up

The key to outwitting the proverbial wall is prevention. Fueling up properly with carbohydrates before a run can usually prevent bonking, unless the run is excessively long. Everyone's body is different, so it may take some trial and error to discover your perfect formula for fueling up. It's generally advised that distance athletes consume a diet that is around 55 to 65 percent carbohydrates to provide needed energy. Avoid fatty foods before exercise, as this can slow the digestion of carbs. During runs lasting more than an hour, it may help to ingest gels, energy bars or carbohydrate drinks. Just 20 grams of carbs can give you a quick blood sugar boost during a run.

Precautions and Suggestions

Talk with your doctor before starting a new exercise program. If you are diabetic or have a history of hypoglycemia, be extra vigilant to prevent blood sugar crashes. Carry a quick sugar source during runs, such as glucose tabs, to catch sugar drops before they become serious.

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