Muscles use glucose to do work, so your blood sugar levels get lower during exercise. This level will go even lower if there is a lot of insulin in your blood. Although the amount of food needed to prevent low blood glucose during or after exercise is different for each person a few general adjustments in your snacks can make a difference.

Check your blood sugar before you exercise

Before you start exercising check your blood sugar.

  • If your blood sugar is below 150 mg/dl before exercising, have a snack of 15 grams of carbohydrate: a piece of fruit, a serving of starch or a serving of milk.
  • If you have problems with low blood sugar much later after you have exercised, have a snack of 15-30 grams of carbohydrate within 30 minutes of finishing the exercise. This will help your body replace the glucose normally stored in muscle and to prevent low blood sugar later. This could be a sandwich, or 4-8 cookies.

If you are exercising immediately before or after a meal, you may be able to reduce the insulin you use to cover your meal, because the exercise will reduce your blood sugar, which normally increases after a meal.

Do you mow the lawn on Saturdays?

If you work behind a desk Monday through Friday and you mow the lawn on Saturdays, you may want to change a few things in your meal plan. Remember that muscles use glucose when you do physical work, so if you eat the same amount of food and take the same amount of insulin, you can expect your blood sugar to be lower on the day when you are more physically active.

To prevent your blood sugar level from going too low, you can do the following:

  • Eat more carbohydrates with breakfast.
  • Decrease your morning dose of insulin. About 20-40% less insulin is usually needed to allow for an hour of yard work.
  • Eat a mid-morning snack to prevent hypoglycemia.
  • Let your grass grow.

Final word

Physical activity is good for you; it helps you use insulin more efficiently and as a result, a given amount of insulin has more power in lowering your blood sugar. This is why insulin doses should usually be decreased before and after exercise.

These positive effects of exercise can last for up to 24 hours after the exercise has ended, but you need to be careful because it can also cause low blood sugar. Exercise can sometimes result in low blood sugar that night or the next day. This is called “delayed-onset low blood sugar”.

Always keep in mind that exercising during the day can result in low blood sugar during your sleep that night or even the next day. Whenever you exercise strenuously, it is a good idea to check your blood sugar more frequently.


I am Andy Carpenter and I would start by saying that I have a Bachelor Degree in Nutrition Science conferred by California State University, Los Angeles and that I am certified as a Registered Dietitian.

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