This is the continuation of an article started in the last issue discussing type 2 diabetes and how to manage blood sugars during and after exercise. A number of key ideas regarding the fundamentals of fuel metabolism in conjunction with exercise were discussed in the first article in Fall Equinox, Vol. 4, No. 2. I recommend you review the information since it is relevant to this article.
Type 2 diabetes is typically the result of the following breakdowns in glucose regulation :
- increased insulin resistance in the body tissues
- decreased insulin output by the pancreas
- excessive glucose output by the liver.
Therapies for type 2 diabetes are varied and will change over time as the disease progresses. Insulin resistance, insulin production and excessive liver glucose production all change over time and require adjustments in therapy. As discussed in the last issue the nature of the diabetes therapy will determine the degree of risk of low blood sugars and the necessary precautions to take before exercising. We will get to that later but first let’s elaborate on the benefits and risks associated with exercise.
Benefits Of Exercise
There are numerous benefits of a regular exercise program and they are listed in table 1. I will highlight a few of my favorites here. One of the immediate benefits, besides having fun and feeling good, is the reduction in blood sugar. There is typically an immediate reduction in the blood glucose levels towards normal in response to exercise. The immediate reduction of blood glucose levels with exercise can actually be used to help regulate blood sugars on a daily basis and can lead to long-term improvement in diabetic control. Exercise can also produce a long-term improvement in insulin sensitivity and decreased fasting/after-meal plasma insulin levels when performed on a regular basis (3-5 times a week).
Table 1. Benefits of exercise for patients with Type 2 Diabetes
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Another benefit is the potential for improved cardiovascular fitness, decreasing the risk for heart disease and increasing energy levels and stamina. In turn these can result in an enhanced sense of well-being and an improved quality of life. Exercise can also result in an improved lipid profile (cholesterol) with research showing lower levels of bad cholesterol (LDL and triglycerides) and higher levels of the good cholesterol (HDL) with a minimum of 10-12 miles per week of moderate intensity jogging. Often there is a reduction of hypertension (high blood pressure). This can occur independent of weight loss or changes in body composition, although these typically occur as well. One of the greatest benefits, however, is the potential to reverse the underlying mechanism of insulin resistance that can lead to diabetes in the first place. Exercise tends to reduce this resistance and increase insulin sensitivity enabling the body to regulate blood glucose (BG) levels more effectively with less insulin. This can be important in the prevention or the delay of onset of type 2 diabetes as well as the treatment.
It was back in the 1970’s that researchers first proposed exercise as a way to treat insulin resistance associated with type 2 diabetes. What they found was that physically active people with diabetes had lower fasting levels of insulin as well as lower insulin levels following a glucose challenge when compared to untrained diabetics of the same age and weight. The exercise resulted in increased sensitivity to insulin and therefore the pancreas didn’t need to produce as much insulin to achieve a similar glucose level. Exercise has been shown to increase insulin-stimulated glucose disposal by 30-35% and this correlates with increased aerobic capacity and is known to be a result of increased uptake of glucose by skeletal muscle and not as a result of reduced liver output of glucose. Glucose disposal refers to the removal of glucose from the circulating blood and into body tissues.
The beneficial effects of insulin sensitivity associated with exercise are lost when exercise is discontinued. The time frame is not entirely clear. There is some evidence indicating that much of the effect is lost after 60 hours while other studies indicate it can last as long as 5 to 7 days. It has even been shown that a single bout of exercise in untrained individuals can increase insulin sensitivity for 2-5 days. So although the effect doesn’t last forever it does last for a while and this can reduce the total insulin requirements and improve overall blood sugar management. The mechanism is not entirely understood but is believed that it may be related to increased capillary density in skeletal muscle, increased oxidative capacity of skeletal muscle and increased skeletal muscle GLUT 4 glucose transporter content. In other words the muscle has more blood vessels, can burn glucose more effectively and has more shuttles to move the glucose out of the blood and into the muscle tissues.
Interestingly enough the research seems to indicate that even though there is improved insulin stimulated glucose uptake as a result of exercise there doesn’t appear to be any improvement in fasting blood glucose levels. There is however, a reduction in the HbA1c indicating that overall blood glucose management is improved as a result of regular exercise. For those of you who may not be familiar with the HbA1c it stands for glycosylated hemoglobin and represents an approximation of the 3 month average of the blood glucose levels weighted more heavily on the more recent levels. It is proposed that the improved HbA1c is the result of frequent episodes of lower blood glucose levels associated with exercise and the after effect of prolonged reduced blood sugars which results in a lowering of the average blood sugar.
For those of you who enjoy weight lifting you’ll be glad to know that a recent study (3) showed a significant reduction in HbA1c as a result of high-intensity resistance training.
A group of 47 type 2 diabetics, men and women, were randomized to either 1. modest weight loss or 2. modest weight loss in conjunction with high-intensity resistance training. The group was 60-80 years of age and used diet and/or medication to manage their diabetes. They were all overweight, sedentary, were not taking insulin and had a HbA1c between 7-10%. All research participants were placed on a healthy eating plan with the intention of a weight loss of 0.25 kg per week. The exercise group attended the gym 3 non-consecutive days per week. Each session included a 5 minute warm-up and cool-down with 45 minutes of high-intensity resistance working both the upper and lower body. Instructors supervised the workouts to ensure proper technique and to assess the workload.
After 6 months both groups had similar changes in terms of weight loss, reduced waist circumference, reduced energy intake, no change in blood lipids, no change in fasting insulin and glucose.
The benefits seen in the training group were a greater reduction in HbA1c, increased strength, a greater reduction in blood pressure and increased lean body mass. Keep in mind this was the result of a high-intensity workout program and perhaps would have yielded even greater improvements had the training group done some other activity on the days between workouts. This type of workout may not be for all individuals as we will discuss shortly in the Risks section and should only be pursued with the approval of your physician or diabetes specialist.
Risks of Exercise
The risks of exercise are listed in table 2. Yes it is a rather large list and for that reason it is highly recommended that you consult your physician and/or diabetes specialist before starting an exercise program. You can even present them with this list if you wish to be sure they are aware and they can tell which risks apply to you. Exercise can increase the risk of having a low blood sugar either during or after the activity. We will discuss this in much greater detail shortly. It is important to mention that individuals with proliferative retinopathy (eye damage) should be cautious with respect to certain exercises which may cause retinal or vitreous hemorrhage. Exercise with the head lower than the rest of the body (eg. sit-ups, certain yoga moves etc) should be avoided as should extremely strenuous exercise or exercise that raises the blood pressure beyond levels recommended by your doctor. Also exercise that results in rapid or jarring head movements should be avoided because of increased risk of hemorrhage or retinal detachment.
Table 2. Risks of exercise for patients with Type 2 Diabetes
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Type 2 Diabetes Therapy
If you have peripheral neuropathy be cautious of high-impact exercising and always keep an eye on the condition of your feet. Watch for any blisters or lesions and treat them appropriately. Frequent and generous foot care should be part of the daily routine of anyone with diabetes.
If you have any heart problems be sure to get specific instructions from your doctor regarding maximum heart rate, maximum blood pressure and symptoms to watch for such as extreme breathlessness, chest pain, joint pain etcetera. With an appropriate choice of exercise and a bit of planning most of these complications can be avoided.
A common risk that presents the most immediate concern for many individuals will be hypoglycemia (low blood sugars), either during or after exercising. To better understand this risk we need to understand the approaches to type 2 diabetes therapy. Perhaps a better understanding will eliminate some of the mystery and result in safer and healthier routines before, during and after exercise.
Last issue we categorized type 2 diabetes therapies based on the risk for low blood sugars. I have listed them on the following page as a reminder, and we will now discuss them in more detail in relationship to exercise. Refer to Table 3 for a list of symptoms associated with low and high sugars.
| Symptoms of Hypoglycemia (Low Blood Sugar) and Hyperglycemia (High Blood Sugar) | |
| Lows: Sweats Shakes Hunger Dizziness Fatigue Irritable Fast Heartbeat |
Highs: Extreme Thirst Frequent Urination Dry Skin Drowsiness Blurred Vision |
- This first category representing the lowest risk will include individuals taking any of the following:
- No Diabetes Medications
- Metformin
- Acarbose
Generally speaking when someone is first diagnosed with type 2 diabetes their physician or diabetes specialist will recommend a period of lifestyle modification (ie. diet and exercise); a minimum 6-8 weeks to see if average blood sugars can be reduced, that is a lowering of the HbA1c. Historically, prior to the discovery of insulin and the development of oral diabetes medications, this was the only way to treat type 2 diabetes. If lifestyle modification fails it will be recommended that some form of medical therapy be introduced. Typically this will be a drug called metformin that acts by reducing sugar output from the liver to help reduce the average blood glucose (BG) levels, especially morning fasting sugars which are often high as a result of an overactive liver during the night.
A second drug Acarbose may also be used, either alone or in conjunction with metformin. This medication acts by reducing glucose absorption from the small intestine thereby reducing the blood glucose rise associated with food intake. In any of the above circumstances there is no danger of ever having a serious hypoglycemic reaction. In some rare circumstances the BG levels may go as low as 3.5 mmole/litre but the body would certainly respond by turning up sugar production and reducing insulin secretion to avoid a further decline in blood sugars. Therefore, if your therapy falls into this category you should never let a fear of low blood sugars deter you from pursuing physical activities. Also do not use the fear of a low blood sugar as an excuse for bingeing during or after exercise. You may get hungry during and/or after exercise but that is no reason to overreact or take in excessive carbohydrates. Take in healthy balanced nutrition, not just carbohydrates.
- The natural progression of diabetes is such that BG control may deteriorate over time and another medication is often added, typically an insulin secretagogue. There is a wide range of these currently available but the underlying principal is the same. These drugs stimulate the pancreas to secrete more insulin. This second category of therapy includes the addition of a secretagogue, typically with metformin but sometimes without and poses an additional challenge in terms of BG management. The challenge is that when taking a secretagogue it is possible that the pancreas may produce too much insulin relative to the blood sugar and results in a severe decline in BG for which the liver cannot compensate. In this scenario BGs may go so low that a coma and possibly death can result.
- Eventually there may be further deterioration of BG control and the addition of another medication called an insulin sensitizer (eg. Avandia) which makes the body more sensitive to the insulin it produces. This class of medications is proving to be an excellent therapy for many type 2 diabetics. In some cases it has been found effective as a first line medication. An insulin sensitizer taken alone poses little risk for a severe hypoglycemic event but if taken in conjunction with an insulin secretagogue, as is often the case, it will increase the possibility of a low BG since the body will now be more responsive to the insulin it produces.
- Many people with type 2 diabetes eventually require or may even choose insulin injections to help them manage their blood sugars effectively. I say choose because some individuals would rather inject a hormone that would occur naturally in the body than introduce a variety of drugs that the body’s liver must process. Insulin may be taken with or without oral diabetes medications. When taking insulin subcutaneously the risk of having a low blood sugar is increased, especially if it is fast-acting mealtime insulin. Even more so if insulin is taken with an insulin sensitizer such as Avandia.
These represent four therapy categories and if you have type 2 diabetes you will fit into one of them. Review your diabetes therapy and decide which category applies to you. This is meant to provide a guide for knowing what your relative risk is for hypoglycemia, especially during and after exercising, but also for activities such as driving and day to day living. Knowing what your risk level is helps you to take the necessary precautions for safety and also lets you manage your blood sugars effectively. Equally important you can live life to the fullest knowing your blood sugars are safely in range and you are prepared if they should dip into the unsafe range.
You should consider yourself at risk for low blood sugars if you are using either a secretagogue or injecting insulin. If by chance you are at risk for severe hypoglycemia during exercise be aware of what your blood sugar is before you start exercising and take appropriate action if you feel you are at risk of low blood sugars during your activity. Appropriate action may include a snack before the workout or simply having some carbohydrates with you just in case of a low or a severe low. If you have an exercise partner it is wise and considerate to inform them that you’re diabetic and the appropriate action to take if a low BG occurs. Generally speaking you should pay attention to any symptoms of a low BG that you experience and take action early rather than waiting until a mere low BG becomes a severe low BG. Let past experiences be your guide. Do your low blood sugar episodes come on gradually or do they happen rapidly with only a small amount of warning time? Do you manage things better with a solid snack or does a liquid carb source seem to enable you to deal with the crisis better and avoid the overcompensating as often happens after a low blood sugar? Learn from your experiences and let the lessons empower you to manage your blood sugars effectively so you can enjoy exercise and life to the fullest.
Eric Norman is a research scientist investigating heart disease in post-menopausal women and in individuals with type 2 diabetes.
References
- Exercise in patients with Type 2 Diabetes Mellitus. Horton, E.S.. Chapter 77 in Diabetes Mellitus: A Fundamental and Clinical Text. Second Edition. Editors Derck LeRoith, Simeon I. Taylor, Jerrold M. Olefsky. Lippincott Williams and Wilkins. 2000.
- Fuel Metabolism, Exercise and Nutritional Needs in Type 1 Diabetes. Franz, M.J.. In Canadian Journal of Diabetes Care 22:4 pp 59-63.
- High-Intensity Resistance Training Improves Glycemic Control in Older Patients With Type 2 Diabetes. Dunstan, D.W. et. Al.. 2002. Diabetes Care Vol. 25, No. 10. 1729.