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ExCarbs, a New Way of Control Through Exercise


Jul 1, 1995

This article is part of an exercise chapter from the authors' new book, Stop The Rollercoaster, written with Lois Jovanovic-Peterson, MD. The book explains the use of multiple injections, carb counting, blood sugar patterns, and reducing risks for complications. Stop the Rollercoaster will be available from Torrey Pines Press (800) 988-4772 in September. For a diabetes update and information on the internet, set your browser to diabetesnet.com.

This is the second of two articles on ExCarbs (AKA, Extra Carbs for Exercise) as a system for maintaining blood sugar control during exercise. The first article [June] showed how to translate exercise into carbohydrate equivalents, called ExCarbs. Almost any exercise can be translated into carb equivalents measured in grams. If this amount of carbohydrate with no insulin coverage is eaten to balance the exercise, blood sugar control can be maintained. See ExCarb Table 1 in the June article to calculate these equivalents.

The underlying theme of these articles is that exercise doesn't have to mean loss of control. With the help of the ExCarb system, and some carb counting and calculations on your part, control can be maintained during exercise. Once you know how many ExCarbs are needed to balance an exercise, you can choose to:

  1. Eat all of these ExCarbs (advantages: easy to do, good for maintaining your current weight), or
  2. Use the ExCarbs as a guide to lowering your insulin doses (advantages: good for weight loss, great for limiting quantities of food during long periods of exercise), or
  3. Some combination of the two.

The first approach, eating all the carbohydrates which are burned while exercising, is the most straightforward approach and was covered in the June article.

In this month's article, we're covering the second and third approaches. We'll show how ExCarbs can be used to guide the lowering of insulin doses, and how extra carbs can be combined with less insulin.

Who is the ExCarb system for? It can help anyone doing any level of exercise or physical work who wants to understand how their exercise affects their blood sugar control. But it has special benefits for those who use an insulin pump or take multiple injections. It is also useful for those who have learned how to use insulin in a physiologic way:

  1. So that N, L, or UL insulin (usually injected twice a day), or the basal rate on a pump keeps their blood sugar level while fasting,
  2. So that the meal Regular or meal bolus keeps the blood sugar controlled with meals, i.e., that meal doses vary to match the amount of carbohydrate in each meal, and
  3. So that a precise dose of Regular will safely lower any high blood sugar reading to normal.

Although using insulin in a physiologic way requires more injections or an insulin pump and is not for everyone (those with gastroparesis, for example), it offers tremendous benefits for people who desire a freer lifestyle with better control. In some European countries, physiologic use of insulin is the norm for treating type I diabetes, whereas in the less diabetes-enlightened United States probably fewer than a quarter of all type Is are using insulin in this way. It is likely that more than 90% would benefit from this progressive approach offering better control with a more flexible lifestyle. Using multiple injections, with each injection meeting a particular need, also has tremendous advantages for improving control with exercise, especially when combined with the ExCarb system.

ExCarbs As A Guide To Insulin Reductions

Lowering insulin doses is a good way to balance exercise. This helps those who want to lose weight and those participating in long periods of exercise who don't want to consume the large portions of ExCarbs required. Lowering the insulin dose allows more fuel to be obtained from internal stores of glycogen and fat, rather than from eating additional food.

Training makes a tremendous difference in insulin adjustments. Exercises in which you rarely participate are likely to require larger insulin dose reductions than those that are routine. Most people doing regular exercise have already lowered their routine insulin doses to compensate. They usually require smaller decreases in their doses because they have already enlarged their glycogen stores and are already on reduced insulin doses. But in starting a weekend canoe trip or training for a marathon, major insulin reductions will likely be needed.

But when do you lower the insulin dose for exercise? There are general guidelines to go by. When exercise lasts 30 minutes or less, it is usually easier to simply eat the small amounts of carbohydrate needed, rather than think about lowering insulin doses. But as exercise stretches beyond 30 to 45 minutes, and a higher percentage of fuel comes from blood glucose, a reduction in the insulin dose is more likely to be needed. This is often done by lowering the dose of Regular given to cover the meal that occurs before exercise. As activities stretch to 90 or 120 minutes and beyond, the long-acting insulin (or basal rate on a pump) will likely need to be lowered. (Table 3 offers guidance on this.)

When Would I Lower My Insulin For Exercise?

In lowering insulin doses, one of theWho is the ExCarb system for? It can help anyone doing any level of exercise or physical work who wants to understand how their exercise affects their blood sugar control. first questions that comes to mind is: How long before my exercise should I lower an insulin to ensure the blood insulin level will actually be lower when I start? In those without diabetes, the blood insulin levels are very responsive and will drop within the first 15 minutes of starting even moderate exercise. But with diabetes, one has to consider which type of insulin is being lowered to know when to lower it. There is always a lag between when a dose of insulin is injected and when the level of that insulin actually starts to change in the blood.

If injected Regular or a pump bolus is lowered for a meal prior to exercise, the blood insulin level begins to "drop" 45 to 60 minutes later. If the basal rate on a pump is lowered, there is at least a two to three hour wait for the insulin level in the blood to drop. If one wants to lower the effect from a longer-acting insulin, the wait is even longer. These lag times between when insulin doses are lowered and when the blood insulin level actually starts to drop will, of course, be shortened when some of the speedier monomeric insulins, like lyspro, become available in 1996. Table 1 provides a rough timetable to show how long after the lowering of various types of insulin an actual drop in the blood insulin level will occur.

The 450 Rule

How can ExCarbs be used as a guide to lower insulin doses? Once someone knows how many carbs are equivalent to their unit of Regular, a close estimate of insulin dose reduction can be made. Long-acting insulins, of course, are harder to translate into ExCarbs because of their long action times, although Table 3 provides guidance on this.

The key to translating carbs into Regular insulin is provided by the 450 Rule. This rule, developed from John's clinical experience, says that the number of grams of carbohydrate covered by one unit of Regular can be found by dividing 450 by the average total daily insulin dose. This rule provides an approximation only for someone with type I diabetes.

For instance, someone who requires 30 total units of insulin each day will need about 1 unit of Regular for every 15 grams of carbohydrate (450/30 = 15), while someone else who uses 50 units a day will need about 1 unit of Regular for each 9 grams of carbohydrate (450/50 = 9).

Let's try using the 450 Rule to look at lowering insulin doses. We'll calculate an insulin dose reduction for someone who weighs 150 pounds and uses 38 units of insulin a day. If we divide his daily average insulin dose of 38 units into 450, we get 11.8. Let's round this to 12. This calculation tells us that one unit of Regular should cover about 12 grams of carbohydrate (provided we take about half of our insulin as NPH, L, UL, or the basal rate on a pump). For the 30 minute run at 8 mph mentioned earlier, we calculate needing at most 72 grams of carbohydrate to compensate for the run. Knowing this, we can easily figure that the run will be equivalent to 72 grams/12 grams per unit or 6 units of Regular.

Most likely, the exercise would not be completely balanced by lowering insulin. Rather, a combination of ExCarb intake and insulin reduction would be used. If we decided to eat 24 grams of carbohydrate, we could apply the other 48 grams toward reducing our insulin doses by 4 units. Dr. Carol Wysham at the Rockford Clinic in Spokane has her patients split this insulin reduction between the Regular and long-acting insulins. So for a morning run, a person could lower his/her breakfast insulin by 2 Regular and 2 L or NPH, and eat an extra banana equal to 24 grams of carbohydrate.

Keep in mind that the 450 Rule works only for those with type I diabetes who use an insulin pump or multiple daily injections in a physiologic way. See the checklist in Table 3 to make sure you can use the 450 Rule, then refer to the table to estimate your own carb coverage. Discuss using this system with your personal physician before any attempt is made to actually use it.

Unfortunately, with type II diabetes, the 450 Rule can't be used with precision because an unknown portion of the total daily insulin dose comes from the person's own internal production. This makes it impossible to know the "total" daily insulin dose. In this case the translation of carbs to units of Regular might be estimated by their personal physician, but cannot be accurately estimated by the 450 Rule.

How Far Can I Reduce My Doses?

There are limits to how far insulin doses can be lowered. Let's say your current insulin dose is correct (i.e., your control is quite good). You start a strenuous exercise program in preparation for running a marathon. With multi-mile runs on training days, you earn enough ExCarbs to seemingly replace your entire insulin dose. But can your insulin be eliminated if you exercise long enough?

With type II diabetes, maybe. But with type I diabetes, definitely not. The limit on insulin dose reduction is revealed by what happens to insulin levels in marathon runners who don't have diabetes. During maximum training, their blood insulin level will drop no further than to half of its original level. This tells us that in type I diabetes, the insulin doses can be reduced no more than 40% or 50% from the original dose even with the most intense exercise programs.

It seems obvious, but we'll repeat: never take any dose of insulin that seems inappropriate. If you usually take 3 units of Regular for your meal prior to the start of your exercise and your blood sugar control has been great, never take more nor less than this amount, even if suggested by the ExCarb system, the 450 Rule, or any other rule.

Combined Adjustments

So we've covered eating ExCarbs and lowering insulin doses as ways to balance your exercise. What about combining the two? General recommendations for combined carbohydrate and insulin adjustments are given in Table 3, modified from Pumping Insulin. Both the intensity of an exercise and its duration will affect how exercise needs to be balanced through adjustments in carb intake and in doses of meal Regular or longer-acting insulins. Basically, the longer and the more strenuous an exercise, the greater the adjustment required, and the more likely it is that insulin doses will have to be lowered.

The length of an exercise is easy to determine, but intensity is a different matter_this can only be estimated. Intensity is highly specific to each individual. Two people may be running side by side at identical speeds, but one may be running at maximum intensity, while for the other the same exercise may be mild.

"Mild" exercise is any extra activity that is relatively easy for you to do, such as casual walking. "Moderate" exercise involves something that makes you breathe harder, but which you could do for some time, such as brisk walking or jogging. "Intense" exercise involves anything that causes deep breathing, but still allows you to carry on a conversation. Examples are race walking or a steady fast bike ride.

If you cannot carry on a conversation while exercising, your effort is beyond "intense" and into the anaerobic range. Examples of anaerobic exercise would be the 100 yard dash and power weight lifting. During short periods of anaerobic exercise, the blood sugar may rise despite seemingly adequate insulin levels because glucose is mobilized very rapidly from glycogen stores to supply fuel. This can overwhelm the current insulin level and cause the blood sugar to go up. If experience shows that the blood sugar rises after this type of exercise, check with your physician for more specific instructions on insulin adjustments.

Tying It All Together

In planning for exercise, consider these four points:

  1. How long and hard am I going to exercise?
  2. How many ExCarbs will I use? (see table in June article)
  3. What's my current insulin level? (Am I having frequent highs, lows, or both? If my blood sugar is high, am I low on insulin and need more in order to exercise, or did I recently take enough insulin and am just high temporarily? Do I need to lower doses more because this is a new or longer exercise, or less because I'm already trained for it?)
  4. Do I want to use my ExCarbs as food to eat, as a guide to reduce my insulin doses (Table 2)*, or as a combined adjustment (Table 3)*?

* Never adjust your insulin doses on your own without first discussing these changes with and getting approval from your physician.

ExCarbs is an excellent system for both exercising and maintaining a much better handle on control. It is important to remember, however, that absolute rules are never entirely possible because so many factors like insulin doses, training, effort, wind resistance, grade of the course, and stress hormone levels vary from individual to individual and from event to event. Also keep in mind that carbohydrate is the nutrient most important to athletic performance. Therefore, some intake of carbohydrates during any longer exercise is required for maximum performance.

Exercise can make you feel and look younger, especially if you understand how to master your blood sugar control in the process. Exercise also appears to be a major way to reduce risks of complications and live a healthier life. Let us know how ExCarbs work for you.

For the list of references, please see "ExCarbs Part One" in our June issue.

John Walsh and Ruth Roberts are the authors of Pumping Insulin and My Other Checkbook. If you have any questions, please write to John Walsh and Ruth Roberts c/o Diabetes Health, 3715 Balboa Street, San Francisco, CA 94121.


Categories: Blood Glucose, Blood Sugar, Book Reviews, Diabetes, Exercise, Fitness, Food, Insulin, Insulin Pumps, Losing weight



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