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. It’s best to speak to your healthcare team about this.
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.
Speak to your healthcare team to get help to create the right plan for you.
Carbohydrate intake before exercise
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.
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.
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.
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.
If you exercise in the late evening after dinner, it may increase the risk of a hypo overnight, often around 2-3am. To reducing 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.
Carbohydrate intake after exercise
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 hypoglycaemia.