Adjusting food and insulin around exercise can be tricky, as different types of exercise can have a different effect on you.
You’ll need to find the right plan that works for you before, during and after exercise, but exercise offers a range of benefits:
- enhanced muscle mass
- improved heart health
- decreased stress and tension
- weight control
- positive mood, overall mental health
People with type 1 may enjoy additional advantages, such as:
- consistent insulin sensitivity
- better balance, stability and joint function
- potential lowering of cholesterol levels
- insulin dose reduction
Before you exercise
Having too much active insulin before you exercise can cause a hypo, as it reduces the amount of glucose the liver can add to blood. Exercising with too little insulin stimulates glucose production from the liver, which can cause a hyper. So you may need to reduce your insulin before you exercise, depending on what you’re doing and how long you’re doing it for.
Preparation is important. Knowing how your body will react to exercise and being prepared to respond are key to all athletic activity.
Whether you need to eat carbohydrate immediately before exercise will depend on your blood glucose level, the type of exercise you plan to do, its duration and its intensity. Everyone’s carbohydrate requirements for exercise are different so checking your blood glucose before, during and after exercise will help you develop your own plan.
Carbohydrate intake during exercise
If you are exercising intensely or over an extended period of time you’re likely to need extra carbohydrate during exercise. Less carbohydrate is required the longer it was since your last insulin injection.
Different types of exercise affect blood glucose levels differently
Different intensity and types of exercise affect blood glucose and insulin levels differently. Sometimes, there is an increased risk of hypoglycemia (low blood glucose); other times, the risk is of hyperglycemia (high blood glucose). And just as different types of exercise correspond with different physiological responses, the body also has varying responses to training versus competition. Something else to keep in mind: athletes with type 1 have increased potential for injuries too.
In general, sustained and moderate exercise (like hiking) will result in a slow drop in blood glucose levels. Intense, sprint-like exercise that really gets your heart pumping (like a game of football or netball) might cause your blood glucose level to rise. This is because your body releases high levels of adrenalin that trigger your liver to break down stored glucose and release it into your bloodstream. It will be exaggerated if your insulin levels are too low at the time of exercise.
Intensity, speed, environment and duration all affect the body’s reaction
There are three types of exercise:
Aerobic exercise is usually continuous, light-to moderate intensity exercise and includes activities like running, walking, long-distance swimming, biking or tennis. Aerobic exercise typically tends to lower blood glucose levels.
Anaerobic exercise is generally shorter in duration, maximum intensity and includes activities like sprinting, gymnastics,or weight training. Anaerobic exercise typically tends to raise blood glucose levels.
Mixed exercise is combination of the aerobic and anaerobic activity such as basketball or football. Managing blood glucose levels with mixed exercise is difficult, but using a tool like a continuous glucose monitor can help greatly.
Glucose levels during sports affect performance in many ways: strength, stamina, speed, agility, flexibility, safety and mental sharpness.
Insulin resistance, which is when the body requires more insulin to process glucose, can be difficult to manage. Exercise combats this by increasing insulin sensitivity and glucose uptake by muscles.
Exercise thwarts postprandial (after-meal) hyperglycemia by slowing carbohydrate absorption, increasing glucose utilisation and accelerating insulin action.
Practice vs game day – each can have dramatically different effects on your type 1. Adrenaline and stress both raise blood glucose levels and are typically present on the day of your game or event.
Balancing Act: Finding your blood glucose and PEAK fitness zone
Caution: Delayed Onset Hypoglycemia can occur typically 6 to 12 hours (sometimes 24 hours) after exhaustive exercise, due to replenishment of muscle glycogen stores and enhanced insulin sensitivity. It is possible to prevent this by:
- Keeping records of your fitness regimen and the effects it has on your body
- Using a CGM or frequent blood testing to monitor your body’s response to activity
- Decreasing basal insulin or meal boluses after activity
- Consuming slow-acting carbohydrates after activity
Similar recording and monitoring tactics can be used to prevent hyperglycemia (blood glucose highs). Some other options include:
- Bolusing (at a half dose) 30 to 60 minutes prior to activity to offset rise of blood glucose, delayed bolusing or adding post-workout cool-down (depending on conditions of rise)
- Incorporating relaxation, breathing, visualization tools to address pre-workout emotional stress
- Limiting pump disconnection time
- Administering rapid-acting insulin (only under certain conditions)
A lack of insulin, due possibly to poor absorption, illness or missed doses—can cause ketone production. This can lead to ketoacidosis, dangerously high levels of ketones and blood sugar.
Some ways to prevent ketoacidosis:
- Check for ketones prior to exercise when blood glucose levels are high for no apparent reason
- Do not exercise when ketones are positive
- If you have missed a dose of insulin, put off exercising until you have adjusted for it
- Do not disconnect pump for more than 90 minutes without replacing insulin
Plan ahead and take precautions to keep exercise and blood glucose in balance.
After you exercise
Be aware the around eight to 12 hours after you exercise, your blood glucose level could drop too low. This is because your adrenalin levels drop and your muscles and liver will start to take up extra glucose to replace their stores. You will need to take this into account when estimating your insulin dose prior to, or immediately after, exercise.
Checking your blood glucose before and then every few hours after exercise, and recording what exercise you do and food you’re eating, will make it easier to see trends and assist you and your healthcare team to develop good ways of managing it.
After dinner exercise may increase the risk of a hypo overnight, often around 2-3am. To reduce the risk of this, you might need to take less evening insulin or eat a low GI snack before bed. If you use an insulin pump, reducing the basal rate can help.
In general, if your insulin levels during exercise were sufficient, your blood glucose should be back down to your pre-exercise level within three to six hours, without additional insulin.
If your blood glucose level is normal to low immediately after exercise, you may need to eat some carbohydrate as your body will continue to cause a slow drop in blood glucose levels. You may also like to consider consuming additional low GI food to protect against delayed post-exercise hypo.
Always talk to your health care team if you feel unsure about anything.
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- How one teenager copes with type 1 while aspiring to become an Olympic athlete
- What triggers the wrath of the immune system
- Insulin supplies and a no-deal Brexit
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- And much more!
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