For general information about exercise, please refer to the health management section. General exercise guidelines are presented below.
The goal of this checklist, and the FAQs is to help ensure more predictable blood sugar results, and especially to prevent low blood sugars.
- Know your blood sugar before starting any significant activity or exercise. If you are low, you need to eat a rapidly acting carbohydrate snack. If you are high, you may need to delay your exercise. If you exercise when you have ketones or when the blood sugar is very high, you will drive blood sugars even higher.
- Check the blood sugar level as needed throughout exercise.
- Be prepared to snack. Snack as needed to prevent low blood sugars during exercise. Ideally, the snack should be a liquid or readily absorbed form of simple carbohydrate.
- When deciding how many carbohydrates to eat, take into account the type, duration and intensity of the exercise, as well as your pre-exercise blood sugar reading. Know, too, how much insulin is still active from the last injection.
- If the activity is prolonged, carbohydrate snacks are periodically required. For example, if you are biking uphill, you will need to check blood sugars frequently, stay hydrated and drink a sports drink (or get an equivalent amount of carbohydrate from some other source such as dextrose tablets) every 20 to 30 minutes or so to prevent hypoglycemia.
Warning: Do not take insulin to cover exercise-related snacks or snacks used to prevent or treat a low blood sugar!
- Will exercise cause a low blood sugar?
- When should your insulin dose be adjusted?
- What kind of food should I take to prevent or treat a low blood sugar during exercise?
- Does the time of day of the exercise matter?
- Is your exercise predictable?
- Have you been drinking alcohol while exercising?
- Are you sick or stressed?
- How long does the blood sugar lowering effect of exercise last?
- Is your blood sugar unexpectedly high following exercise?
- Are you trying to lose weight?
Will exercise cause a low blood sugar?
In general, the longer, more vigorous, and more intense the exercise, the more likely that the exercise will lower the blood sugar. So when you are exercising, you may need to lower the dose of your insulin and eat more carbohydrates to prevent a low blood sugar related to exercise. The lowered insulin dose may include using a temporary basal and taking less insulin coverage at meals eaten just before and just after the activity. The converse also is true – brief, non-strenuous exercise may not require any insulin dose or diet adjustment.
When should your insulin dose be adjusted?
Because exercise generally increases insulin sensitivity, a lower dose of insulin may be needed. Exercising every day may require an overall reduction in your total daily insulin dose. Exercising every once in a while may require a dose reduction just on the day of your intermittent exercise. In practice, this usually means taking lower bolus insulin doses just before or just after the exercise.
When exercise is unplanned, it is important to think about how much insulin is on board. If there is a lot of insulin still acting (such as from a recent insulin bolus to treat a high blood sugar correction or meal or the peak effect of a long-acting insulin), the insulin combined with any significant exercise could result in a low blood sugar. If you are worried about having relatively too much insulin for the exercise, the solution is to eat more carbohydrate or delay the exercise until the insulin wears off.
Check with your health care provider for specific dose adjustment recommendations.
What kind of food should I take to prevent or treat a low blood sugar during exercise?
It may be necessary to eat a carbohydrate-containing snack to prevent a low blood sugar. Ideally, the snack should be a liquid or readily absorbed form of simple carbohydrate. Remember that complex carbohydrate takes a longer time to digest. If the food is high fat or oily, the stomach will empty more slowly and the absorption of the sugar is delayed. High-fat or complex carbohydrate containing snacks may increase the risk of exercise-related low blood sugars.
Is it better to exercise at a certain time of day?
Factor in the time of day. Many people will have natural changes in their insulin sensitivity throughout the day. This is called “diurnal (daily) insulin sensitivity”. There are several common patterns, such as insulin resistance in the morning with increased sensitivity throughout the day, or the opposite – insulin resistance at the end of the day and at night, but sensitivity in the morning. Various in-between patterns are also a possibility.
This is important because, if you exercise when you are more insulin-sensitive, you may be at greater risk for a low blood sugar. To prevent this, you need to take less insulin and eat more carbohydrate. The converse also is true. Exercising during periods of resistance may have fewer blood glucose-lowering effects, so fewer adjustments to insulin dose and carbohydrate intake may be needed. Check with your diabetes provider to understand your own daily or diurnal insulin sensitivity pattern.
Try to exercise at the same time of day, for the same amount of time and at the same level of exertion. This will ensure the most predictable blood glucose response. Whenever you exercise, you have to match the duration and intensity of exercise with other factors such as natural body rhythms or changes in insulin sensitivity that occur throughout the day, peak insulin effect and the content of meals.
Have you been drinking alcohol while exercising?
Remember! Alcohol alone can reduce the amount of glucose produced by the liver, and can predispose you to a low blood sugar
Alcohol and exercise in combination increase the risk of a low blood sugar.
At first this may sound odd. Who would drink alcohol while running or swimming? However, consider if you are both drinking and dancing. Both activities promote low blood sugar, and this can lead to such severe lows that you pass out. Should that happen, it might be difficult to know whether you have had too much to drink or are suffering from low blood sugar.
Understand what happens when you’re sick, stressed, or fatigued.
Any sort of stress will make you less sensitive to insulin. If you are sick or stressed or exceptionally fatigued, you will release more glucose counter-regulatory hormones. As a result, the exercise may have less of a glucose-lowering effect.
How long does the blood sugar lowering effect of exercise last?
The blood-sugar lowering effect of exercise can vary in duration. Depending upon your level of physical training, and the intensity and duration of exercise, you may be more sensitive to insulin for hours or even into the next day after exercise. When you exercise every day, you body becomes overall more sensitive. However, if you stop exercising, in a few days the increased sensitivity will wear off as well.
Here are some points to keep in mind:
- People who work out or are physically active on a daily basis may need to lower their total daily insulin dose. This decrease can be up to 30% or more for well-trained athletes.
- For people who exercise more sporadically, the acute effect of exercise on insulin sensitivity may last hours to half-a-day – and they may need to reduce their insulin dose just before or after the activity.
- Unusually prolonged or vigorous activity may result in a decrease in insulin dose requirements, overnight and even into the next day.
Is your blood sugar unexpectedly high following exercise?
When the blood sugar is unexpectedly high after exercise, think about why. Generally, exercise will lower your blood sugar. If the post- exercise blood sugar reading is unexpectedly high, you may need to consider if your blood sugar dropped so low during the activity that your body re-regulated itself by releasing counter-regulatory hormones. If so, the subsequent rebound can cause a high blood sugar reading. Other considerations might be overestimating the impact of the exercise, engaging in a stressful kind of exercise (such as weight lifting) and eating too much carbohydrate beforehand.
Are you trying to lose weight?
Try to optimize your dose of insulin so that you can avoid exercise related low blood sugar reactions and the need for extra exercise-related snacks. Fewer snacks means fewer calories!
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