A New Way To Handle Exercise
"The only way to get positive feelings about yourself is to take positive actions. Man does not live as he thinks, he thinks as he lives."
Rev. Vaughan Quinn
This article is part of an exercise chapter from the book, STOP The Rollercoaster (now Using Insulin) , written with Lois Jovanovic-Peterson, M.D. This book covers interesting ways to use multiple injections, carb counting, blood sugar patterns, reducing risks for complications, and more.
Much of this information comes from the authors'personal experiences. John and Ruth's preferred exerciseis biking. Their experience includes an 1100 bike ride, three rides between San Francisco and San Diego,two centuries under full load, and three "hell"rides between Tecate and Ensenada in Mexico. Otherathletic accomplishments: 23 mile canoe trip, several day walks beyond 20 miles, diabetes team triathelons, and the remodelling of 12 houses.
They've presented work shops on carb counting at three of the last five International Diabetic Athletes Association Conferences, and discussed exercise effects with a wide range of endurance athletes. John and Ruth are on the Board of Directors of the IDAA, and John has provided clinical care for a wide variety of athletes in San Diego.
People with diabetes often associate exercise withloss of control. Like others, they want to exercise because it makes them feel better and improves their health. But what happens? A long walk, some rollerblading, or painting a house, and their blood sugar drops. Eating a candy bar then sends the blood sugarsoaring. Some extra insulin to correct the high and the blood sugar goes low again.
Exercise often introduces confusion to control. A systematic approach is hard to come by. Instead, people often respond to problems after they occur, thinking "I'll start my exercise, then check my blood sugar and take care of problems later," or the unfortunate alternative "I won't exercise at all."
It's true that absolute rules in exercise are never entirely possible because so many factors like insulin doses, physical fitness, physical effort, wind resistance, grade of the course, and stress hormone levels vary from individual to individual and from event to event. But in this article we show how exercise can be balanced more closely.
This article introduces ExCarbs, a brand new system that allows exercise to be effectively balanced by eating replacement carbohydrates and by adjusting insulin. Extra Carbs for Exercise, or ExCarbs, provide the yardstick to measure the impact an exercise will have on the blood sugars.
ExCarbs can be eaten to replace carbohydrates burned by physical activity or exercise. By replacing this carbohydrate before, during, and/or after the exercise, blood sugar control can be maintained. No insulin is taken to compensate for ExCarbs. In addition, ExCarbs can be used to guide insulin dose reductions for those who want to lose weight, and for those who don't want to eat large amounts of carbohydrates during long periods of exercise.
So, you have choice. Once you know how many ExCarbs are needed to balance an exercise, you can choose to:
- Eat all of these ExCarbs (advantages: easy to do, good for maintaining your current weight), or
- 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
- A combination of the two.
The first approach, eating all the carbohydrates which are burned while exercising, is the most straightforward approach. But the second and third approaches have distinct advantages, too. We'll show how to do all three.
Who is the ExCarb system for?
It can help anyone doing any level of exercise or work, who wants to understand how exercise affects their blood sugar control. But it has special benefits for those who use an insulin pump or multiple injections and have learned how to use insulin in a physiologic way:
- So that longer-acting insulins, like N, L, UL, or Lantus, or the basal rate on a pump, keeps their blood sugar level while fasting,
- So that the meal doses of Humalog or Regular (or meal boluses from a pump) keep the blood sugar controlled with meals, i.e. that doses vary to match the amount of carbohydrate in each meal, and
- So that a precise dose of Humalog or Regular can safely lower any high blood sugar reading to normal.
Where Does The ExCarb System Come From?
The calories of energy consumed in different types of exercise are easy to determine from standard tables developed by exercise physiologists over many years. For mild exercise like walking, carbohydrates contribute 30% to 40% of the total calories burned. As the intensity of exercise rises, the portion of total calories burned from carbohydrate also rises, reaching about 70% of total calories during strenuous aerobic exercises like running a marathon.
In Table 1, we've translated various types of exercise into grams of ExCarbs. The numbers listed are usually the maximum amount needed per hour of exercise to prevent a low. Table 1 provides the key information for maintaining control during a wide range of physical events. Adjustments have been made to compensate for the intensity of an exercise. As outlined in the last column of the table, a smaller percentage of total calories will come from carbs during milder exercises, but as exercise intensity rises, so does the percentage of calories that comes from carbohydrate. The last column also illustrates the importance of choosing higher carbohyrate foods when participating in intense, vigorous exercise.
As an example of how to use the table, if you weigh 150 pounds and walk 3 miles in an hour, you'll use 300 calories of energy. (Not shown in the table.) During this mild walk, around 30% of the total calories, or about 90 calories, will come from carbohydrate. (most of the other 70% come from fat stores for this mild exercise.) These carbohydrates come from a variety of sources, but mainly from glucose stored in muscle, glucose removed from the blood, and carbs that are eaten. All of these carbs have to be replaced within a few hours of an exercise.
Since there are 4 calories in each gram of carbohydrate, about 22 grams (90/4) of carbohydrate will need to be eaten for this one hour walk. This 22 grams is equal to an average-sized apple, or to a cup of milk plus a graham cracker. If you walk at this same pace for 2 hours, you'll need 44 grams of carbohydrate, and for a shorter 30 minute walk, about 11 grams. But if you run the same 3 miles at a speed of 8 mph, you'll need about 65% of your energy as carbohydrate. This comes out to 54 grams of carbohydrate for this run lasting 22 minutes or more than twice the amount needed for the leisurely one hour walk!
Carb Counting and Exercise
With most flexible insulin therapy programs, the longer acting insulin (or basal rate) is first adjusted to keep the blood sugar normal and level while fasting. Then the carbohydrates in each meal, measured in grams, are balanced with a premeal dose of Humalog insulin matched to that amount of carbohydrate. John, for example, uses 1 Humalog for each 14 grams of carb. (As noted, fat and protein do have some effects, but these are minimal.)
ExCarbs can then be added as needed to balance exercise or they can be translated into an equivalent insulin dose reduction. (See the 450/500 Rule.) Any exercise that can be translated into calories, and most can, can also be translated into the grams of carbohydrate it will burn. The carbohydrate can be measured and replaced. Carb counting gives you the best handle on the effect that both meals and exercise will have on your blood sugars.
Attention to carbohydrate intake is important not only for blood sugar control but also for athletic performance. "An excellent diet cannot make an average athlete great, but a poor diet can make a great athlete average." Although fat and protein can act as fuels during exercise, endurance begins to suffer if the amounts of fat and protein are too high in the diet. This is especially seen when exercise is long or intense.
Diets low in carbohydrate rob the muscles of the glycogen stores they need for endurance and performance. For example, a trained marathon runner on a high carb diet can run for about 4 hours before exhaustion sets in. But when on a high fat, low carb diet, the same athlete will become exhausted in less than an hour and a half, long before a marathon ends.
Athletic performance faces another challenge in diabetes. Endurance suffers not only when the diet is low in carbohydrate, but also when the blood sugar goes high or low. A high or low blood sugar means that glucose delivery to muscles as fuel is impaired and thus can directly affect performance. With diabetes, both the replacement of carbohydrate consumed by exercise, and the balancing of this carbohydrate intake with matching insulin doses become critical to maximum performance.
To improve their performance, athletes eat a diet high in carbohydrate and load up on carbs just prior to major exercise events. Carb counting is very popular among pumpers, athletes, and others who want great control. For complete instructions on carb counting, see the Carb Counting section, or obtain a copy of the Pocket Pancreas or Pumping Insulin.
ExCarbs As Carbohydrate Replacement
The simplest way to keep blood sugars normal while exercising is to eat extra carbohydrate. To do this, look up your planned exercise in Table 1, then, through carb counting, eat foods with this amount of carbohydrate to maintain control.
As noted, carbohydrates make up only part of the total calories used during any particular exercise. The remaining calories come mostly from fat and a lesser amount from protein. Although fat and protein calories can affect weight and insulin doses moderately in the long-run, they have little immediate effect on blood sugars compared to carbohydrates. So to offset exercise, you first want to determine how many total calories the exercise uses, and then find out what portion of these total calories are coming from carbohydrate. These carbohydrates needed to balance exercise are ExCarbs. Table 1 lists some ExCarb values for you.
When Are ExCarbs Replaced?
The ExCarb table tells us how many total carbs are required, but we also need to know when to replace them. Even if the blood sugar is normal before exercise, all of these carbohydrates are not replaced before the exercise starts. As one example, during 30 minutes of moderately strenuous exercise, like running at 8 mph, about half of the fuel comes from carbs, roughly 40% from internal glycogen stores in leg muscles and the other 10% directly from the blood. Only the glucose obtained from the blood has to be immediately replaced by eating or by new production of glucose. Even when insulin levels are high, glycogen use during this 30 minute run rises only to 50% with another 16% coming directly from the blood.
During the first 30 to 45 minutes of exercise, local muscle glycogen stores provide about five times as much glucose as the blood. But as the same run continues beyond 30 minutes, more carb fuel comes directly from the blood. The blood glucose contribution climbs to about 40% and the insulin level quickly drops by 50% under normal circumstances during the first 2 hours of exercise.
However, if insulin levels are high, the portion coming from the blood and needing immediate replacement would again be raised. The more insulin, the more eating required. Excess insulin blocks release of fuel from large internal stores in muscle glycogen and in fat pads. Eating becomes critical to the supply of fuel whenever insulin levels are high.
In many circumstances, though, most of the carbohydrate burned during exercise will come from these internal stores. If there is an appropriate insulin level when exercise starts, these internal glycogen stores begin releasing their stored glucose as fuel for the exercise. Then following exercise, internal glycogen stores are rebuilt over the next 3 to 36 hours. This is done through a gradual removal of sugar from the bloodstream. The longer and the more intense an exercise, the longer it takes to rebuild these glycogen stores.
This is why all the ExCarbs do not all have to be eaten right away. It is also why the blood sugar tends to go low in the hours following a long period of exercise, especially during the night. Many athletes with diabetes routinely add a portion of their ExCarbs to their bedtime snack to prevent this nighttime drop.
Replacing spent exercise energy with a matched amount of ExCarbs provides an excellent way to balance short periods of exercise, usually those that last less than 45 minutes. But as the length and intensity of exercise increases, so does the need to lower insulin doses. Luckily, as we'll see, ExCarbs can be translated into equivalent units of Humalog or Regular insulin as a way to better estimate these insulin dose reductions. Lowering the insulin dose allows more fuel to be obtained from internal stores of glycogen and fat, rather than from eating. How to do this and how to make combined adjustments are covered below.
ExCarbs as a Guide to Insulin Reductions
The second way to offset exercise is to lower insulin doses. 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 often 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 Humalog 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 often need to be lowered.
In lowering insulin doses, one of the 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 an injection of Humalog or a pump bolus of Humalog is lowered for a meal so that the exercise following the meal is less likely to lower the blood sugar, the insulin level in the blood will begins to "drop" 15 to30 minutes later, and stay lower than after a normal meal coverage for 3 and a half hours. If the basal rate on a pump with Humalog is lowered, there is usually at least a 90 minute delay before the insulin level in the blood actually drops. If one wants to lower the effect from a longer-acting insulin, the wait is even longer. These long 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 Humalog. Table 2 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 be seen.
Table 2: How long before your exercise should you reduce each of these insulins
so that you have less insulin in your blood as you begin exercising?
Meal Humalog or Humalog bolus: 15 to 30 min.
Meal Regular or Regular bolus: 30 to 45 min.
Basal rate on a pump: 90 minutes to 3 hours
NPH or Lente: 4 to 8 hours
UL: 10 to 24 hours
Lantus: 24 hours
The 450 or 500 Rules
How can ExCarbs be used as a guide to lower insulin doses? Once someone knows how many carbs are equivalent to a unit of Humalog or 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 4 provides guidance on this.
The key to translating carbs into Humalog insulin is provided by the 500 Rule, and with Regular the 450 Rule is used. This rule, developed from John's clinical experience, says that the number of grams of carbohydrate covered by one unit of Humalog can be found by dividing the number 500 by the average total daily insulin dose. This rule provides a close approximation for how many grams of carbohydrate will be covered by 1 unit of Humalog. It works best for those with Type 1 diabetes. The number 450 gives a better estimate for those using Regular insulin.
For instance, someone who requires 25 total units of insulin each day will need about 1 unit of Humalog for every 20 grams of carbohydrate (500/25 = 20), while someone else who uses 50 units a day will need about 1 unit of Reg. for each 10 grams of carbohydrate (500/50 = 10).
Let's try using the 500 Rule to look at lowering insulin doses. We'll calculate an insulin dose reduction for someone who weighs 150 lbs. and uses 40 units of insulin a day. If we divide his daily average insulin dose of 40 units into 500, we get 12.5 which is rounded up to 13. (Table 3 is helpful for translating the 500 Rule.) This calculation tells us that one unit of Humalog should cover about 13 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/13 grams per unit or 5.5 units of Humalog.
Most likely, the exercise could not be completely balanced by only lowering the insulin doses. Rather, a combination of carb intake and insulin reduction would be used. For instance, if the runner decided to eat 33 grams of carbohydrate, he could apply the other 39 grams toward reducing his insulin doses by 3 units. (Dr. Carol Wysham at the Rockford Clinic in Spokane has her patients split this insulin reduction between the Humalog and long-acting insulins with good results.) Following this strategy, for a morning run, a person could lower his/her breakfast insulin by 2 units of Humalog and 1 unit of L or NPH, and eat an extra carbs equal to 33 grams of carbohydrate.
Keep in mind that the 450 and 500 Rules work best for those with Type 1 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 450/500 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 2 diabetes, the 450 and 500 Rules are not as precise in their estimate because an unknown portion of the total daily insulin dose will come from a person's own internal insulin production. This makes it impossible to know the true "total" daily insulin dose. In this case the translation of carbs to units of Humalog might be estimated by the personal physician, but cannot be accurately estimated by the 500 Rule. The estimate for carb coverage obtained from the 500 Rule will usually underestimate true insulin need in Type 2 diabetes, ie, it tends to be safe to use when covering carbohydrate intake, but may underestimate how far insulin doses need to be reduced for exercise, especially if blood sugars are well-controlled in someone with Type 2 diabetes.
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 2 diabetes, maybe. But with Type 1 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 1 diabetes, the insulin doses can be reduced no more than 40% or 50% from the original dose for even the most intense exercise programs like running a marathon.
It seems obvious, but we'll repeat: never take any dose of insulin that seems inappropriate. If you usually take 3 units of Humalog for your meal before you begin your normal exercise and this dose has been working great, never take more nor less than this amount, even if suggested by the ExCarb system, the 500 Rule, or any other rule.
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 4, 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 Humalog or longer-acting insulins. Basically, the longer and the more strenuous an exercise, the greater the adjustment required, and the more likely 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 are the 100 yard dash and power weight lifting, During short periods of anaerobic exercise, the blood sugar can 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.
What If The ExCarb System Doesn't Work?
The greatest problem in maintaining control with exercise shows up when the current insulin doses have not been correctly set. Insulin doses that are set too high or low create problems in fuel delivery. A key question to ask if the ExCarb system is not working is, "Are my current insulin doses set properly?"
An example of someone with insulin doses set too high is a person who has frequent low blood sugars in the afternoon, but who decides to start exercising at 3 p.m. anyway without first lowering their insulin dose or eating extra Excarbs. The insulin reaction that follows will now be quite severe, but should not be blamed on the exercise. Blame it instead on the underlying excessive insulin level.
Another example of excess insulin would be someone who takes a large dose of Regular just before eating a meal that contains lots of carbohydrates. Even though this dose matches the carbs in the meal, two hours later the blood sugar has risen to 300 mg/dl because the injection was taken just before eating and hasn't yet begun to balance the food. The person, confident he is safe, goes out for a 6 mile run. The severe insulin reaction 45 minutes after the 300 reading should again not be blamed on the exercise. Humalog is less likely to cause this type of imbalance.
An example of insulin doses set too low is someone who wakes up in the morning with a reading of 180 mg/dl, and then goes jogging for 30 minutes. She is surprised when her blood sugar has risen to 240 mg/dl on her return. Again, the exercise is not to blame. Rather, the underlying lack of insulin allows the liver to begin producing glucose, and encourages muscle glycogen stores to break down rapidly with the release of even more glucose into the blood. Meanwhile, the lack of insulin also prevents glucose from moving across cell membranes into muscles for use as fuel. Her blood sugar control would likely have been aided with a small dose of Humalog before starting her jog or even better by maintaining blood sugar control during the previous night.
One's training level can also play havoc with readings. Whenever we start a new exercise, we use more glucose than normal because our muscles are poorly trained and inefficient. Stimulated by the new exercise, these underpowered muscles immediately begin to enlarge their glycogen stores by removing extra glucose from the blood. This raises the risk for a low blood sugar. Once muscles have become trained for this particular exercise and glycogen stores have been built up, this excess drop will no longer be seen.
Another less predicable factor is the counteractive effect of stress hormones on insulin. This often occurs at the start of a competitive event, like a swim meet, a 10K run, or a century bike ride. Nervousness at the starting line comes from the release of stress hormones, which cause stored glucose to be released, independent of the insulin level. Blood sugars often rise unexpectedly in these circumstances.
Problems can also creep in when exercise conditions change. If you usually walk 2 miles on flat ground, but decide to walk the same distance in hilly country, you'll use more fuel in climbing these grades. A strong headwind can increase carbohydrate consumption by about 1% for each extra m.p.h. of headwind (i.e., for a 10 m.p.h. headwind, increase carbs by 10%). Walking in dry sand or soft snow can easily double the amount of carbohydrate needed for the same walk on firm ground.
Problems can also arise for activities that have uneven pacing, like spring-cleaning or football, where it's hard to predict whether you'll spend the next hour sorting through the closet for throwaways or moving furniture, or spend the entire game on the bench or on the field. Luckily, most activities don't suffer from this unpredictability.
Tying It All Together
In planning for exercise, think of these four steps:
- How long and hard am I going to exercise?
- How many ExCarbs will I use? (see Table 1)
- 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?)
- Do I want to use my ExCarbs as food to eat, as a guide to reduce my insulin doses (Table 3)*, or as a combined adjustment (Table 4)*?
* Never adjust your insulin doses on your own without first discussing these changes with your physician and getting approval.
ExCarbs are an excellent system for both exercising and maintaining a much better handle on control. 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.
The following references are provided for readers who desire additional information:
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- E.W. Bannister and S.R. Brown: The relative energy requirements of physical activity. Exer. Physiol. New York, N.Y., Academic Press, 1968.
- E.T. Howley and M.E. Glover: The caloric costs of running and walking one mile for men and women. Medicine and Science in Sports 6: 235, 1974.
- G. Bray: The acute effects of food intake on energy expenditure during cycle ergometry. Am. J. Clin. Nutr. 27: 254, 1974.
- H.T. Edwards, R. Margaria, and D.B. Dill: Metabolic rate, blood sugar, and the utilization of carbohydrate. Am. J. Physiol. 108: 203-209, 1934.
- D.L. Costill: Carbohydrate nutrition before, during, and after exercise. Fed. Proc. 44: 364-368, 1985.
- M.J. Franz: Nutrition: Can it give athletes with diabetes a boost? Diab. Ed. 17:163-171, 1991.
- M.C. Foss, et. al.: Hormone-fuel metabolism during exercise of insulin-dependent diabetic patients treated with an artificial B-cell unit. Acta Diabetol. Lat. 26: 185-194, 1989.
- J.F. Yale, A. Leiter, and E.B. Marliss: Insulin resistance during recovery from strenuous exercise is greater in obesity. Int. J. Obes. A: 108, 1985.
- P. Felig and J. Wahren: Role of insulin and glucagon in the regulation of hepatic glucose production during exercise. Diabetes 28(1): 71-75, 1979.
- A. Schiffrin and S. Parikh: Accommodating planned exercise in Type 1 diabetic patients on intensive treatment. Diabetes Care 8: 337-342, 1985.