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Low blood sugar levels during exercise: is non-diabetic hypoglycemia threatening?

30th May 2015


Hypoglycemia is the term used for defining low blood sugar levels, and when we’re talking about non-diabetic hypoglycemia, we refer to below normal values of blood sugar that occur in people who aren’t affected by diabetes. The symptoms of hypoglycemia can vary from one person to another, and can be accentuated by certain factors such as the lack of sleep, fasting or dehydration.

Triggers of hypoglycemia in non-diabetic people can be very different, but today we’ll only discuss about exercise-induced low blood sugar levels, and we’ll try to understand why this symptom occurs, how threatening it is and how it can be prevented and managed.

Why do some people experience exercise-induced hypoglycemia?

 

Exercise can decrease one’s blood sugar levels, but in healthy people the hypoglycemic episode is only temporary. If you constantly experience low blood sugar levels after or during exercise, it may be wise to schedule an appointment with your doctor and get tested for diabetes. Problems with the adrenal and pituitary glands, as well as liver problems, may also trigger hypoglycemic episodes, so it’s important to exclude any potential health issue from the list.

Back to exercise-induced hypoglycemia: you probably experienced it several times after strenuous exercise, so the symptoms may sound very familiar. Hypoglycemia manifests through dizziness, headaches, inability to focus, shaking, sweating, blurred vision, irregular heartbeats, and even loss of coordination, anxiety and seizures if you don’t restore the glycogen reservoirs fast after the first symptoms occur.

Why do these manifestations appear when exercising? Your body relies on glucose as its main fuel, so this form of sugar is the first one used by the organism for producing energy during exercise. The muscles and brain require glucose to function properly, and glucose is stored in the liver and muscle cells in the form of glycogen. Intense or long workouts can deplete these reservoirs, and once your body runs out of glycogen, hypoglycemia occurs.

The blood sugar level is more likely to drop during exercise in people who have stronger and bigger muscles, because muscles are responsible for about 90% of the body’s use of glucose. So even if non-athletic individuals may also experience hypoglycemic episodes while exercising intensely, those with a higher percentage fat-free mass and bigger muscles are more prone to this symptom.

Exercising on an empty stomach increases the risk of hypoglycemia, as the body’s glycogen reserves are used faster when there’s no extra sugar in the blood stream. Normally, the organism would first use the blood sugar, so if you have a snack before working out, the glycogen in muscles and liver will only be used after the blood glucose is consumed.

If you skip breakfast and go directly to gym in the morning, after having a very low amount of carbs for dinner one night before, it’s likely that you’ll experience hypoglycemia. This will affect your exercise performance and may become threatening if you don’t grab a sugary snack fast when the symptoms start manifesting, so it’s recommended to have a small snack like a banana or an energy bar before the workout, or to make sure you get enough carbs for dinner, to start the day will your glycogen reservoirs full.

An important aspect to keep in mind is that your body starts using glucose at faster rates as soon as you begin to work out, and it first takes the glucose from the bloodstream for powering the muscles. After about 15 minutes it switches to glycogen stores in liver and muscles, and once these reserves are gone, it turns to fat for energy production.

Preventing hypoglycemia during exercise

For an unfit person who eats about 50% of their calories from carbs, the stored glycogen should be enough for powering the muscles for about 1 hour and 30-45 minute of exercise. For a fit person though the blood glucose and stored glycogen may only be enough for 1 hour of strenuous exercise, and for someone who’s on a low-carb diet, the glycogen reserves may be emptied even faster.

Still, this doesn’t mean everyone will experience hypoglycemia. Healthy people who follow a low carb diet can train their bodies to use mostly fat for fuel, through a process called ketosis. We’ll discuss ketosis in another article, but right now let’s see how one can prevent hypoglycemia from occurring during exercise.

One of the easiest things to do is to grab a snack before exercising, or to have breakfast before the training session, if you work out in the morning. Doing endurance training instead of strength training also helps, as endurance exercise burn mostly fat for fuel, while strength training empties the glycogen stores faster.

If you mix both endurance and strength training in a single session, start with 20-30 minutes of moderate-intensity endurance exercises (60-70% of your maximum heart rate), and end the routine with 15-20 minutes of intense strength exercises. Then grab a glass of orange juice or some figs or a small banana after the workout, to prevent hypoglycemic episodes on your way back home.

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