Anne L. Peters, MD; Bruce W. Bode, MD


June 23, 2015

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Anne L. Peters, MD: Hi. I'm Dr Anne Peters. I am here today with Dr Bruce Bode to talk about exercise as part of the treatment for diabetes. Let's start the discussion. You and I both take care of lots of athletes. How do you teach someone how to take care of a person who is taking insulin?

Bruce W. Bode, MD: As you know, exercise is an insulin sensitizer; it makes insulin work better. In type 2 diabetes, you always want to get your patients to walk because it improves insulin action. In type 1 diabetes, they don't make insulin, so they need to take insulin to survive. You have to balance the insulin with their food intake. When they exercise, you're going to need less insulin because they will have improved insulin action and sensitivity.

For people with type 1 diabetes who want to exercise, and especially those who want to get into extreme exercise like running a marathon, you have to help them and guide them. You have to balance the insulin with glucose levels. You have to have the right amount of insulin and match it with carbohydrates as best as you can. The rule of thumb is that you always start exercise when your glucose level is above 90 mg/dL and preferably don't start exercise if your glucose level is above 250 mg/dL because that means you are relatively insulin-deficient.

If you are starting at 90 mg/dL, you might want to take 10-20 g of carbohydrate before you start, even juice or something. Then, the key is that you need to monitor the glucose in response. If somebody is doing aerobic exercise like running or walking, and over time they start to fall, that means that they have too much insulin on board. You have to cover that with carbohydrates. The rule of thumb is: For every 30 minutes of exercise, you need between 15 g and 30 g of carbohydrate. They can get them from a drink or a bar. You don't need any fancy food or anything. All of that is important during exercise.

After exercise, you need to make sure that their glucose levels aren't going to go low because, all of a sudden, insulin action has improved dramatically. The rule of thumb is: If you're exercising for more than 35-45 minutes, you need to replenish your glucose stores. With exercise, you've depleted some glycogen from your muscles and liver, so you have to restore that. You need to restore it with 40-80 g of glucose after exercise, especially strenuous exercise like cycling for 50 miles or doing a 5 or 10K. You always need to replace your glucose with carbohydrates. It doesn't matter what type of carbohydrates.

Dr Peters: A favorite carbohydrate of my college students is peanut butter and jelly sandwiches. Do you have a favorite food or snack that people have after exercise?

Dr Bode: I think peanut butter and jelly is fine. You have the two breads on each side, you have the jelly, and you have the protein.

Dr Peters: Simple, good, and generally not something that people with diabetes can eat. Do you have them take insulin for that or just eat the carbs and test later?

Dr Bode: You need to know where your sugar is. Ideally, if you have a sensor, you can really tell. If your sensor is going up, you obviously need to take insulin. If your glucose level on the sensor is going down, you might want to cut back on your insulin, but you still have to cover that glucose. We typically cover it with about 50% of your usual dose, initially. Let's say that your peanut butter and jelly sandwich normally takes 8 U of insulin. You might take 4 U and see what happens. And then you learn what works for you individually.

Dr Peters: So trial and error is key because not every person is going to be the same, and the adjustments before and after exercise are going to be different.

The Optimal Exercise Prescription in Type 1 Diabetes

Dr Peters: Now I have some very specific questions. If you could write a prescription for exercise, is there a time of day that you would prefer someone to exercise?

Dr Bode: Obviously, exercise is good, so it's whatever works best for them. If I had to say which is better, it would be the first half of the day because the second half of the day is going to affect your glucose in the middle of the night. If you live with a significant other or you have a pump that shuts down when your glucose level goes low, you're fine. But if you live alone and you're prone to hypoglycemia, that can be dangerous. You always want to make sure when you go to bed that you've eaten. The last thing you want to do after exercise is to go out with your friends to celebrate and drink. That's a bad thing. You had a soccer game. Now you're going drinking at the bar, and you don't eat. You could have severe hypoglycemia.

Dr Peters: That's why I always tell people to eat and drink at the same time. I want them to go out for a beer if they want it, but they have to understand that risk. I do find that the hardest time for me to help people manage their glucose levels is when they want to exercise right after work, which is when everything is at the nadir, as far as I can tell. Their cortisol is at the nadir. They are hours away from lunch, and they're going to eat dinner after exercise. I often run into trouble there. Let's say that your patient is exercising at 10:00 AM. Everything is going well. Is there a type of exercise that you would recommend or a pattern? What is the general focus that you would have?

Dr Bode: As you know, there are different types of exercise. Aerobic exercise is something like walking, jogging, or running. There is anaerobic exercise, like weight lifting. There is episodic exercise like sprinting, which is very anaerobic. Anything anaerobic will bring your glucose up. A sprint or going onto the hockey rink and going all out for 90 seconds will bring your glucose up. That's very hard to control because of your adrenaline. But with aerobic exercise, your glucose is being picked up by your muscles all the time because your adrenaline is not as high.

Obviously, it's where your glucose level is. If you are going to go on a long walk, you could truly sprint in order to bring your blood glucose level up by 50 points and then walk. You'll see it gradually go down on a continuous glucose monitoring device. The key is that you always need fuel. Your fuel is glucose. If you have eaten recently, you're fine because you have fuel. At the end of the work day, however, you have no fuel on board. If you're going to bike 50 miles or walk, you're going to need some fuel.

Dr Peters: Yes, the key is to make sure that patients always carry fuel with them. I have had a patient or two who have gone low or are going low, and they didn't have food, so they would sprint, which is not something that I recommend because it's not how you want to treat hypoglycemia in that setting. I have patients who try to follow my advice, and what you are saying holds. They do some sort of anaerobic exercise. They lift weights or even play tennis, where they're being very competitive and their sugar is high after exercise. And they say, "Gee, that's the wrong effect." But I tell them, and I'm sure that you do as well, that exercise is good for you, and we just have to pattern out what they need to do in terms of their insulin dosing.

Dr Bode: Yes, hyperglycemia after exercise is very common. You have a lot of adrenaline. You've been playing tennis hard, and your glucose is high. You don't have enough insulin on board to drive it in. This happens frequently in cyclists after a race, especially the short races. What we have them do is cool down. After exercise, you want to keep your muscles moving. Don't sit down and do nothing. You should walk. If your glucose is high, your muscles will pick up that glucose. You need to hydrate. By doing that, you're sending the glucose back into the muscle and back into the liver. You are rebuilding your glycogen stores, which is crucial. And then, if your glucose level remains high, you need to take a corrective dose of insulin.

Dr Peters: We forgot to mention that hydration is key here. Getting dehydrated is the enemy of everything we are trying to do. Hydration through races, through training, through whatever, is vital. Give me an exercise prescription to give to a patient. It's a 35-year-old person who wants to start exercising. He is taking insulin. Tell me, in 1-2 minutes, exactly what you would tell that person to do. How often do you want them to exercise? What is your prescription for exercise?

Dr Bode: If you haven't been exercising at all, I think the easiest thing to do is walk. If you want to join a gym and get a trainer, that's fine, too. They will work with you. You want to know what your glucose level is going in. You want to measure it, record it, and remember. As you are exercising, you want to see what direction you're going in based on that exercise so that you will know what to do and how to handle it. Let's say that you are walking. Every time you walk, your glucose seems to drop 50 points. That means that you have a good amount of insulin on board. That means that you need to either take carbohydrates as you exercise—typically 15-30 g every 15-30 minutes—or, if you had eaten before, you can cut the insulin down because a lot of people who exercise want to lose pounds.

Dr Peters: Right. They don't want to eat all these extra carbs.

Dr Bode: Yes, so what you do is purposely reduce the insulin by 50%, and that will offset it so the glucose won't go into your cells, and you will have enough glucose to exercise and preserve fuel during exercise. It's a balance. But you have to monitor your glucose and look at what happens before exercise, after exercise, and 4-6 hours after exercise.

Dr Peters: Right, to look for delayed hypoglycemia.

Dr Bode: Yes. And it's always better to eat something 4-6 hours before exercise. You don't want to go in to the gym without having eaten all day. You will have no fuel.

Dr Peters: Right. It's always about the balance: insulin, exercise, fuel. You just have to make it work out. It takes trial and error, but I think that, as physicians, we can really help our patients achieve what they want. I know you and I have both worked with elite athletes who have done all sorts of amazing things. This isn't necessarily a barrier, but it's often perceived as a barrier. Working with one's healthcare team can make a big difference.

Dr Bode: There's no question about it. You should allow people to do whatever they want and learn how to balance it.

Dr Peters: Exactly.

Dr Bode: Continuous glucose sensing will hopefully become standard of care in the next few years.

Dr Peters: I hope so, too. Thank you very much. This has been Dr Anne Peters for Medscape.


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