Exercise Induced Hypoglycemia

Hypoglycemia is the term used to describe a low blood glucose.  A blood glucose level below 70mg/dL is considered hypoglycemia, and often manifests as symptoms including:

  • Fatigue
  • Pale skin
  • Tremors
  • Irritability
  • Tingling Sensation Around the Mouth
  • Dizziness
  • Sweating

Most often, hypoglycemia is associated with diabetes, however, there is a phenomenon known as exercise induced hypoglycemia, or reactive hypoglycemia, that is often seen in non-diabetic, otherwise healthy individuals.

This hypoglycemic response is due to the insulin-like effect of exercise.  The major mechanism for skeletal muscle glucose uptake and disposal involves the glucose transporter GLUT4. GLUT4 needs to be present at the surface of the skeletal muscle cell to bring glucose into the muscle. Typically, the insertion of GLUT4 into the skeletal muscle wall occurs in the presence of insulin, however, insertion of GLUT 4 into the skeletal muscle wall without insulin is possible by skeletal muscle contraction during exercise.  

Avoiding exercise at peak insulin action is paramount.  Insulin is released by the beta cells of the pancreas in response to a raised blood glucose, and will spike at about the 30 minute mark.  Hypoglycemia symptoms can be exacerbated if the effect of both insulin and increased GLUT4 concentration during exercise are combined. For this reason, the consumption of just simple sugars in the 1-2 hours prior to exercise is more likely to induce hypoglycemia during exercise than the consumption of complex carbohydrates, or carbohydrates with other foods, because they are more quickly absorbed into the bloodstream.   

A Few More Facts About Exercise Induced Hypoglycemia:

  • Those with a higher percentage of fat-free mass and larger muscles are more prone to these symptoms, as their muscles are able to store more glycogen.

  • An exercise induced drop in blood glucose may be 50% greater when exercise is performed at midnight, than compared to the morning or afternoon. This correlates to when the circadian hormone cortisol was the lowest and was not stimulated by exercise.

  • Well-trained athletes have more GLUT4 transporters, and their GLUT4 transporters actually work more efficiently than non-trained individuals, putting them at a higher risk of hypoglycemia.  

What to Eat Before Working Out

Exercise induced hypoglycemia can be prevented through proper pre-workout nutrition.  Current sports nutrition guidelines recommend the following carbohydrate (CHO) intake prior to exercising to both prevent hypoglycemia and maximize performance;

  • 4 g/kg body weight CHO 4 hours before exercising
  • 3 g/kg body weight CHO 3 hours before exercising
  • 2 g/kg body weight CHO 2 hours before exercising
  • 1 g/kg body weight CHO 1 hour before exercising

Note: It is not recommended that you intake carbohydrates at every hour; only one of these recommendations is needed.  You can figure out how much time you have before your workout, and choose what recommendation is best for you accordingly.  

It is also recommended to intake about 14-28g of protein 1-2 hours prior to exercising.  

For more information about the current sports nutrition guidelines, refer to the references below.

Examples of pre-workout snacks include:

Bananas

Oatmeal

Cottage Cheese and Fruit

Fruit Smoothie

Apple Slices and Peanut Butter

TO SIMPLIFY, HERE ARE A FEW TAKEAWAYS:

  • If you experience unusual dizziness, fatigue, paleness, and/or tremors during exercise, you may be experiencing hypoglycemia.
  • Make sure you eat properly before you exercise to prevent hypoglycemia. Ingesting simple carbohydrates in particular soon before exercise may exacerbate symptoms.

References:

  1. Coleman, Ellen, and Christine Rosenbloom. Sports Nutrition: A Practice Manual for Professionals. 5th ed., Academy of Nutrition & Dietetics, 2012.
  2. Potgieter, S. “Sport Nutrition: A Review of the Latest Guidelines for Exercise and Sport Nutrition from the American College of Sport Nutrition, the International Olympic Committee and the International Society for Sports Nutrition.” South African Journal of Clinical Nutrition, vol. 26, no. 1, 2013, pp. 6–16., doi:10.1080/16070658.2013.11734434.