Learn How Your Blood Sugars Respond

By Canadian Diabetes Care Guide posted in Physical Activity

Learning how your blood sugars respond is important when you exercise. By taking your blood glucose reading immediately before and after exercising, you will know whether it is safe to begin exercise for that day, and how many points your reading drops due to exercise.

Before exercise, use your blood glucose meter to check that your blood glucose reading is at 5.5 mmols or higher, as it is most likely that you will get a lower number after you exercise. If it’s lower, take 15 grams of a fast-acting sugar, such as a dextrose tablet or a hard candy (not sugar free), and re-check your blood sugar reading in 15 minutes.

After exercise it is recommended that you eat a light snack if your reading is less than 5 mmols, especially if you must drive. Remember “5 to Drive”.


Another reading to be aware of is 14 mmols or greater before breakfast as this is too high to begin exercise.

While a slow walk may help burn extra sugars, moderate to vigorous exercise may cause problems, so postpone exercise until your sugars are back under control.

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The Canadian Diabetes Care Guide's articles are written by Diabetes Professionals for people with diabetes. We provide information about diabetes, diabetes health care providers, complications associated with uncontrolled diabetes and tools to manage their condition. Our mission is to help people with diabetes stay healthy and successfully manage their diabetes.

  • Andrew-Norbert O’Nymous

    Why do you say that we shouldn’t exercise if our readings are over 14? Wouldn’t the exercise serve to reduce it?

    • Alan

      After a meal fats are digested by the body into fatty acids and these fatty acids are absorbed into the bloodstream and some are stored in the body.
      When you exercise the body calls on two types of fuel to generate
      energy – the stored fatty acids and glucose.

      Stimulated by the demand from your exercising muscles your
      body pours glucose into your bloodstream. This glucose cannot get into your
      muscles to produce energy when you do not have enough insulin available to process the glucose and is exacerbated if your BG readings are high (>14).

      The body then looks for alternative sources of fuel and uses
      the free fatty acids for energy. When this fat is used for fuel it results in a
      byproduct called ketones and the ketones accumulate in the blood and spill over
      into the urine.

      The presence of ketones is called ketonuria and further dehydration and ketone accumulation can result in ketoacidosis, which is a medical emergency.