Exercise and type 1 diabetes

Striking a healthy balance 

Prior to being diagnosed with diabetes, you probably lost a considerable amount of weight over a very short period of time. Some of this weight loss was due to fat loss as your body burned fat for energy rather than burning glucose. However, around half this weight loss would have been due to dehydration. As your blood glucose levels rose, your kidneys started to work overtime to filter the excess glucose. It is normal to regain several pounds over the first week after commencing insulin therapy as your body becomes hydrated. During this time, the excess glucose is taken up by the cells of the body and your kidney function returns to normal. 

Over the next few weeks or months, your body will also replace the fat stores lost leading up to the time of your diagnosis. Unfortunately, excess weight gain is a potential side effect of intensive diabetes control with insulin. This may occur if you have recurrent hypoglycemia and/or need to eat excessively to prevent hypoglycemia. High levels of insulin can also prompt your body to store excess carbohydrates as fat, meaning you can still gain weight while eating only healthy foods. It’s not just a matter of what you eat; it is also a matter of how much you eat. If you eat more calories than you burn, you will gain weight. If you eat fewer calories than you burn, you will lose weight. Having diabetes hasn’t changed this equation. 

Ideally, you should eat when you’re hungry. If you need to eat regularly to avoid your blood glucose level dropping too low, you probably need your insulin regimen adjusted. Talk to your endocrinologist or health care team for further advice. As you get older, your metabolism slows down, causing you to put on weight more easily. If you are in your forties, you can no longer eat the same amount of food you did when you were in your twenties and expect to maintain your weight. How active you are during the day will also affect your energy requirements. If your blood glucose levels are normal or high, and you are gaining excess weight, the chances are you are eating too much. 

Surprisingly, the extra pounds from servings that are just a “little” too large can add up quite quickly. Certain foods and drinks, such as pasta and alcohol, are also very high in calories. While you can still eat and drink these foods in moderation, they need to be balanced with the rest of your daily or weekly intake. 

There is no doubt that exercise is good for you. It helps with weight management, reduces stress, and is beneficial for your overall heath. However, adjusting food and insulin around exercise can be tricky, since different types of exercise can have different effects on people with diabetes. 

In general, sustained moderate exercise such as walking will result in a slow drop in blood glucose levels. However, intense exercise that really gets your heart pumping may result in your blood glucose level rising in the short term. This occurs because your body releases high levels of adrenalin that trigger your liver to break down stored glucose and release it into your bloodstream. This reaction will be exaggerated if your insulin levels are too low at the time of exercise. Once you stop exercising, and your adrenalin levels drop, your muscles and liver will start to take up extra glucose to replace their stores. This means you are at risk of your blood glucose level dropping too low in the 8 to 12 hour period following exercise. You will need to take this into account when estimating your insulin dose prior to, or immediately after, exercise.

Test your blood glucose before, and then every few hours after exercise, and record what exercise you do and the food you eat in your blood glucose record book. This will make it easier to see trends and will also assist you and your health care team in developing good management strategies. 

Exercise and insulin action
The key things to consider when exercising are the type of exercise, the action and timing of your insulin, and your carbohydrate requirements. The overall goal is to begin exercise with just the right amount of insulin in the blood. Having too much active insulin at the start of exercise reduces the amount of glucose the liver adds to blood, thereby increasing the risk of hypoglycemia. Conversely, exercising with too little insulin stimulates glucose production from the liver, which can cause hyperglycemia. Exercising in the late evening after dinner may increase the risk of hypoglycemia overnight, often around 2:00 a.m. to 3:00 a.m., but you can reduce this risk by lowering your evening insulin or eating a snack before bed. You should discuss this situation with your endocrinologist or health care team and develop a plan.

When the start time of a sporting event dictates the time of exercise, you may need to reduce your insulin prior to the event. The amount by which you reduce your insulin dose depends on the type and duration of your chosen activity. Generally, the main things to consider when adjusting insulin prior to exercise are the intensity and duration of exercise. Initially, small adjustments are recommended for moderate exercise. Larger adjustments may be needed for prolonged intense exercise. As you get more experienced, you will be able to fine-tune your insulin dose to your individual responses. Adjusting your insulin dose is just like any other component of diabetes management. Getting it right requires practice!

Even when exercise is timed well with insulin action, you may need to eat extra carbohydrates to balance your blood glucose levels. Whether you need to eat them immediately prior to exercise will depend on your blood glucose level, the type of exercise you intend to do, its duration, and its intensity. Everyone’s carbohydrate requirements for exercise are unique. Testing your blood glucose before, during, and after exercise will help you develop your own plan.

If you are exercising intensely and/or over an extended period of time, you are likely to need extra carbohydrates during exercise. How many carbohydrates you need will differ depending on the timing of the exercise relative to the action of the insulin you have injected. In general, you require fewer carbohydrates as the time since your last insulin injection extends.

To help maintain hydration during exercise, you can take your carbohydrate in the form of a carbohydrate-electrolyte beverage, which provides the best available fluid and carbohydrate absorption rates. Other more concentrated drinks such as juice or carbonated drinks have slower absorption rates and can cause an upset stomach. 

After exercise
Your muscles and liver can take up extra glucose to replace their used stores for 8 to 12 hours after exercise. This means that exercise places you at risk of hypoglycemia for many hours after you have finished exercising. This risk is even greater if you have consumed alcohol within the same period or in the hours following exercise.

If your blood glucose levels continue to fall after exercise, you may need to decrease your insulin doses before and after exercise. The amount by which you reduce your insulin will depend on your blood glucose trend. Your endocrinologist or health care team will be able to give you advice about insulin adjustment. 

A reminder that this article is not intended to replace medical advice. Please discuss with your physician what would be considered a normal blood glucose treatment for you.

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