Adjusting Food for Exercise

An important part of managing diabetes is getting regular exercise. Most exercise lowers blood sugar levels. If you take insulin or diabetes pills, your blood sugar may drop too low. Knowing how to control blood sugar levels before, during and after exercise is important. Knowing how to adjust food for exercise will help.

If your blood sugar DROPS with activity:

Exercise can lower your blood sugar because exercise makes your body more sensitive to the insulin it makes or the insulin you inject. In addition, the muscles you use during the activity use up sugar for energy, without the need for insulin.

Your blood sugar can drop during or long after physical activity. However, it is most likely to go low if you:

  • Take insulin
  • Take certain diabetes medications;
  • Skip meals†
  • Exercise for a long time
  • Exercise strenuously

If your blood sugar drops DURING the activity:

  • Stop exercising and use the Rule of 15 to treat hypoglycemia
  • Check to make sure your blood glucose has come back up above 100 mg/dl before starting to exercise again.

If you have ongoing hypoglycemia call your healthcare provider to see if they can recommend a change in your insulin or medication regimen.

For people doing exercise for long periods of time regularly, you may need a combination of medication adjustment along with eating snacks to prevent lows during and after activity.

Some activities may cause your blood glucose to drop quickly while others do not.†If your blood glucose levels are trending down before a workout, have a pre-exercise snack. Always carry a carbohydrate food or drink (like juice or glucose tabs) that will quickly raise your blood glucose.


If you use an insulin pump, you may be able to avoid adding an extra snack by lowering your basal insulin rate during the activity.

How do you know if you need to snack? To decide if you need a snack during exercise, consider the following:

  1. The time that your insulin or diabetes pills work the hardest. Try not to exercise when your insulin or diabetes pills are peaking or working the hardest. Ask your doctor when your insulin or pills peak.
  2. Whether or not you have just eaten a meal. Eating prior to exercising can help blood sugars from dropping, however, if you give insulin at meals, your blood sugar can drop if you exercise when your insulin is peaking.
  3. How long and how hard you will exercise. The longer or harder the exercise, the more sugar the muscles will burn. Keep extra carbs with you to avoid low blood sugar.
  4. Your blood sugar levels. Check blood sugar prior to the exercise. If your blood sugar is less than 100 mg/dL, eat a snack. This will help keep blood sugar from dropping even lower during exercise. People with type 1 diabetes should not exercise if they show ketones in urine or blood.

Are there any special concerns? Low blood sugar may occur for up to 24 hours or even longer, after very intense exercise. To avoid low blood sugar after very hard and long exercise, be sure to adjust your food. Also, check your blood sugar at bedtime. Have a snack if your level is less than 100 mg/dL. Be alert to low blood sugar events for the next 24 - 48 hours.

If your blood sugar INCREASES with activity:

Blood glucose can also go up during or after exercise, especially when you do a high-intensity exercise that increases your stress hormone (i.e., glucose-raising hormone) levels. If your blood glucose is high before starting exercise, check your blood or urine for ketones. If you test positive for ketones, avoid vigorous activity. If you do not have ketones in your blood or urine and you feel well, it should be fine to exercise.

Important Things to Remember

  • Before starting an exercise program, talk with your doctor. Avoid exercise if you have type 1 diabetes and you have ketones in your urine or blood. Talk with your diabetes educator or doctor about the right times for you to exercise.
  • Always carry fast-acting carbs to treat low blood sugar.
  • Drink water before, during and after exercise. Always stay well hydrated.
  • Check blood sugar before exercise.
  • Check your blood sugar every hour if your exercise session is longer than 60 minutes.
  • Watch for drops in blood sugar after very long and hard exercise. Eat a snack when you finish. Be sure to check your blood sugar before you go to bed.

How can your doctor help you? Talk with your doctor about safe exercise for your medical condition. Your doctor may want to adjust your diabetes medicine on days that you exercise.

Blood Glucose & Exercise; ADA website:

Exercise & Type 1 Diabetes. ADA Website: Edited on Dec 7, 2018.