The incidence of diabetes continues to grow in epidemic proportions throughout the western world. Chances are that you, as a fitness professional, are seeing more and more clients who are currently living with diabetes or are at risk for developing diabetes due to obesity, family history and inactivity. At the very least, you should be seeing these people! Understanding the physical and psychological effect that the disease may have on your clients is an important component in your attempts to motivate and inspire.
Those of us who work in diabetes education are continually amazed and impressed by the astounding number of new oral medications, new genetically-engineered forms of insulins and enhanced technologies, which have expanded treatment options and improved care over the last few years. Despite all of these remarkable developments, the cornerstones of great diabetes management (i.e., nutrition and exercise) remain constant and within reach of every person who is living with or at risk for diabetes.
Although there are a number of different types of diabetes, the majority of people living with diabetes have one of two types of the disease. Type 1 (formerly called “juvenile diabetes”) is an autoimmune disease, where the body’s own immune system attacks and destroys the insulin-producing beta cells of the pancreas. Those with type 1 diabetes, many of whom are children or young adults, face a lifetime dependence on insulin injection or infusion, careful blood glucose monitoring and dietary control. It is estimated that 10 percent of people with diabetes have type 1. There is a substantial amount of exciting and promising cure research ongoing in the field of autoimmune type 1 diabetes. And until that cure is here, those people living with type 1 diabetes must use every option available to maintain tight control of blood sugar level, prevent complications and live healthy lifestyles.
Type 2 diabetes (formally called “adult-onset” diabetes) is the most common and fastest rising form of the disease. It is strongly correlated to obesity and a sedentary lifestyle. Insulin resistance is the primary issue in type 2 diabetes. Early in the disease process, the pancreas may be producing or even over-producing insulin; however, resistance to its effect at the cellular level negatively impacts insulin’s ability to control glucose levels. As a result, blood sugar levels rise, sometimes without detection, until advanced symptoms or complications set in. Type 2 diabetes is typically progressive, and while it may begin as insulin resistance accompanied by “relative” insulin deficiency, it often progresses over time to insulin resistance accompanied by “absolute” insulin deficiency. Depending on where in the disease process a person with type 2 diabetes is, sometimes oral medications (pills) taken to address insulin resistance are all that is needed to control blood glucose levels. At other times or in other persons, insulin injections or any combination of the available therapies may be required to best control the disease.
Type 2 diabetes is also often accompanied by a clustering of cardiac disease risk factors such as hypertension, dyslipidemia and obesity. While the disease formally was most common in the adult/senior population, today type 2 diabetes affects all age groups including children. As the risk and incidence of long term complications (such as vascular problems, neuropathies, kidney disease, blindness, etc) increase with duration of disease, the high rate of occurrence of type 2 diabetes in children is nothing short of horrifying to those of us in the public health sector. The good news is that modest weight loss and regular physical activity can both prevent the onset of diabetes and reverse or play a role in controlling type 2 diabetes itself. As fitness professionals, we need to awaken the world to the fact that the power of prevention lies squarely in our own hands.
The diagnostic criteria for diabetes has been continually revised and includes the addition of a new term: pre-diabetes. As of 2006, a lab-drawn fasting blood glucose of 100-125mg/dl places a person in the pre-diabetes category and at high risk for developing diabetes. A fasting blood sugar of 126 or greater is a diagnostic level for diabetes. Once diagnosed, a person with diabetes should learn to utilize a blood glucose meter to assess levels throughout the day. Appropriate use of a meter allows self management education regarding the effects of food, exercise, stress, illness and other variables on blood sugar levels. Although diabetes management goals should be individualized for each person, the objective for most is to maintain as near normal blood sugar levels as possible, without risking severe and dangerous hypoglycemia (low blood sugar). Unless you yourself are living with diabetes, you probably do not realize how many of life’s variables affect blood sugar and how challenging it can be to balance it. Good fitness and nutrition practices are certainly major components in this objective.
As fitness professionals, you should be aware of the recent updates to the American Diabetes Association’s Clinical Practice Recommendations, which address diabetes management around exercise and activity. You will find yearly publications of the clinical practice recommendations on the American Diabetes Association (ADA) website at http://www.diabetes.org/for-health-professionals-and-scientists/cpr.jsp. Those applicable to exercise prescription include the recommendation for appropriate evaluation of the client with diabetes before beginning an exercise program. With permission, fitness professionals should confer with a client’s physician/healthcare team so that an assessment can be made regarding any increased likelihood of cardiovascular disease, contraindications to certain types of exercise or pre-disposition to injury. These will include uncontrolled hypertension (high blood pressure); severe autonomic neuropathy (nerve damage potentially affecting the cardiovascular system, thermoregulation, thirst and slowed digestion); severe peripheral neuropathy (nerve damage affecting the feet, hands and/or peripheral extremities); and advanced degrees of retinopathy or macular edema (complications of the eye). Exercise in the presence of any of these specific long term complications of diabetes may be contraindicated and will need to be prescribed in conjunction with a healthcare professional such as a certified diabetes educator (CDE) who understands these complex situations.
Fitness professionals should also be aware that persons with diabetes are at increased risk of cardiovascular disease and may experience vague or more unusual symptoms of CVD such as shortness of breath, a worsening of exercise tolerance and pressure/discomfort in the mid to upper back, shoulders, jaw or stomach. Some may experience no symptoms at all, which is a situation called “silent ischemia.” Education with the goal of spreading awareness regarding these issues is certainly beneficial. Immediate medical management is of course required in all of these situations, but once stabilized, fitness remains an important component of treatment. Partnering with a clinical exercise physiologist, perhaps through a local cardiac rehabilitation and prevention program, is a great idea for fitness professionals with clients in these categories. Although a bit more challenging, the rewards of keeping people with these diagnoses engaged in regular exercise and committed to good nutrition and a healthy lifestyle are sensational!
Blood Sugar and Exercise
The ADA clinical practice recommendations also provide guidelines that may be helpful in regulating the glycemic response to exercise. Most fitness professionals and people participating in or contemplating exercise probably believe that all exercise lowers blood sugar levels. While that may be true of some exercise, that is certainly not true of all. Many people with diabetes quickly become frustrated with either the increased risk of hypoglycemia (low blood sugar) or the worsening of glycemic control (high blood sugar) that can accompany exercise. Understanding the physiology behind the process helps to reduce the risk and successfully meet the challenge of regulating blood sugar around exercise.
In most cases, mild to moderate aerobic exercise or activity lowers elevated blood sugar levels. The amount of lowering depends on a number of individual variables including:
- Intensity and caloric expenditure
- The effect of diabetes medications (more on this below)
- The amount of circulating insulin at the time of activity
- The amount of insulin resistance relative to that individual
- Time of day
- Recent food intake
On average, a half hour of moderate aerobic exercise such as walking can lower blood sugar level about 50 points. It is important to recognize that a lowering of blood sugar does not happen in people who do not take medications or insulin, which cause a lowering effect, and whose blood sugars start and remain within the normal homeostatic range. Remember that non-diabetic persons who exercise in a normal blood sugar range will maintain that range effortlessly via the well-controlled output of liver glycogen, in most cases regardless of intensity or duration of exercise. People on insulin at risk for hypoglycemia can try balancing the blood glucose lowering effect of a half hour of exercise with 15 to 30 grams of carbohydrate. Testing blood sugar via use of a meter before and after exercise will help diabetics learn to pattern the effect of exercise and will assist in developing predictive strategies and management techniques to balance blood sugar.
In the normal physiologic (non-diabetic) state, insulin levels are instantly dropped by about 50 percent at the onset of activity. During moderate aerobic exercise, when glucose as a fuel is used in greater amounts overall to produce energy, glucose also enters cells via additional pathways other than insulin, hence the greater flux of glucose into cells despite lowered amounts of circulating insulin. Notice that some insulin is required during exercise to regulate blood sugar levels and metabolism. This explains why severely elevated blood sugars in type 1 diabetes (+300-400mg/dl) may not come down with exercise, particularly if there is an insulin deficiency such as a missed or skipped injection. When people with type 1 diabetes are deprived of insulin for 12 to 48 hours and are ketotic, exercise can worsen both the hyperglycemia and the metabolic imbalance (ketosis). In this situation, avoid exercise until both insulin and blood glucose levels are stabilized.
Anaerobic, high intensity, power types of exercise may actually cause an elevation in blood sugar levels during and immediately after exercise. This rise in blood sugar is a result of the role of liver glycogen and hormonal responses to this type of activity. In an experiment measuring insulin and blood glucose levels in non-diabetic subjects in response to the 90 seconds of an all-out maximal effort during the Wingate Cycle speed test, insulin levels rose significantly to maintain appropriate blood glucose levels. In the person with type 1 diabetes, when insulin levels do not rise, intense anaerobic exercise can cause a significant elevation in blood sugar. If you work with clients who observe this response, you should be sure your clients are aware that corrections for elevations relative to exercise should always be conservative as metabolism and insulin sensitivity remains elevated. This places the diabetic athlete at significant risk for low blood sugar as a result of this increased effect of insulin. Remember too that metabolism stays elevated for hours after all types of exercise. This will increase insulin sensitivity as well and may place those with diabetes at higher risk for hypoglycemia, potentially even during the night while sleeping. Persons with diabetes should make a plan with their healthcare providers to prevent overnight blood sugar excursions, particularly after long duration or evening exercise. This may even involve middle-of-the-night blood sugar monitoring, additional carbohydrate in a pre-bedtime snack or both.
Table 1 - ADA Clinical Practice Recommendations ~ Activity
|Metabolic control pre-exercise:
|Type 1: w/insulin deprivation 12 to 48 hours and ketotic, exercise can worsen. If client feels well and no ketones, CAN exercise hyperglycemia.
|Ingest +CHO if BS < 100mg/dl on insulin/secretory agents.
|Generally NA w/diet only, metformin, TZDs, a-glucosidase inhibitors
|BG monitoring before and after (consider during):
|Identify when changes in insulin or food intake necessary.
|Learn glycemic response to different exercise conditions.
|Consume added CHO or adjust medication as needed to avoid hypoglycemia.
|CHO based foods should be readily available w/exercise.
Diabetes Management Tools
As stated previously, the blood sugar lowering effect of aerobic exercise does place at risk our diabetic clients who are on insulin or on oral medications from the class called sulfonylureas (such as Glucotrol, DiaBeta, Glynase, Amaryl, Micronase). This group of medications works in type 2 diabetes to stimulate the pancreas to produce more of its own insulin. Potentially, this can increase the risk of low blood sugar caused by too much circulating insulin, especially when activity levels increase or food intake is delayed.
Other classes of oral medications in diabetes work differently than those discussed above, to address insulin resistance in a variety of ways. Medications in the following classes: biguanides (metformin – i.e., Glucophage); thiazolidinediones or TZDs (Actos and Avandia); Alpha-glucosidase inhibitors (Precose and Glyset); Meglitinides (Prandin and Starlix) do not typically put clients at risk for low blood sugars relative to moderate exercise when provided alone. Recognize that many of these medications are now available in combination – one pill, two different types or classes of medications.
On intake, the fitness professional should pay special attention to client’s medication lists and research the type to identify potential effects on exercise blood sugars. While the guidelines use to advise additional carbohydrate intake for anyone with diabetes whose blood sugars were less than 100 prior to exercise, this is no longer the case. This recommendation is now more appropriately dependent upon the type of medication used to manage diabetes. This guideline DOES still apply to diabetics managed on insulin or oral sulfonylureas as noted above. So clients on insulin or sulfonylurea medications, which place them at risk for low blood sugar, are advised to ingest additional carbohydrate prior to, during and/or after exercise when blood sugars are less than 100mg/dl (see Table 1).
Persons on insulin have a vast array of genetically engineered insulin options available to them. The most common forms of insulin in use today are termed “basal – bolus” therapies and also pre-mixed solutions. Many insulins today are manufactured to provide coverage in a similar fashion to the method of control the working pancreas uses. Today’s long acting or basal insulins such as Lantus and Levemir brands provide long duration background insulin coverage in a 12 tp 24 hour pattern via one or two injections a day. When using this type of therapy, the person with diabetes must also provide “bolus” or mealtime rapid-acting insulin injections (such as Humalog, Novolog or Apidra brand) at each meal to provide additional insulin coverage of food intake. To do this successfully means checking blood sugars before and after each meal and “carb counting” to match the amount of carbohydrate intake to the necessary rapid acting insulin injection. In essence, the person with diabetes using intensive management with basal-bolus insulin therapy must learn to “think like a pancreas.” To best manage blood sugars around aerobic exercise, this may mean compensating to avoid low blood sugar by decreasing the previous mealtime rapid acting insulin dosage, increasing carbohydrate intake or both. It certainly means checking blood sugars more frequently around activity to identify patterns and develop predictive strategies for optimal management.
Other commonly used insulin types include pre-mixed insulins such as 70/30 or 75/25 brands. These are pre-mixed ratios with an intermediate acting and a shorter acting insulin. In considering the effect these pre-mixed insulins have on exercise, you and your client will want to consider the time of peak action of the mixed insulins with regard to time of day of exercise, the time of last meal or snack and the blood sugar levels prior to starting exercise. Your client’s healthcare professional or pharmacist should be able to assist you both in understanding these relationships if necessary.
Insulin can now be administered via injection (by syringe or more commonly an easily portable pen device), an insulin pump (a pager-like computerized device worn externally, which provides subcutaneous insulin delivery continually and, at the press of a button, can be programmed to deliver more or less as needed) or most recently an inhaled version of rapid acting insulin (called Exubera, developed by Pfizer). All of these different versions allow persons with diabetes to maintain tight control while making the disease fit their lifestyle, rather than the other way around.
Today there are also new injectables other than insulin, and they are often used in conjunction with other oral therapies or insulins to help manage blood sugars. Byetta is one of these injectables for Type 2 diabetes in a class called increntin mimetics. Byetta works to self regulate glycemic control by assisting pancreatic beta cells, slowing digestion and promoting weight loss by suppressing appetite within the central nervous system. Symlin (Pramlintide) is another injectable, other than insulin, approved for use in both type 1 and type 2 diabetes. It also works to control the post-meal rise in blood sugar by blocking the release of glucagon. It is injected at each meal and may put patients at risk for severe low blood sugar occurring about three hours after injection. People using Symlin will want to be extremely cautious when exercising at time of peak action and may wish to make a plan with healthcare providers to specifically address the use of Symlin in conjunction with their fitness plan.
A brand new class of oral medications has also recently been added to the type 2 treatment mix. Januvia is the first medication in a new class of drugs called DPP-4 inhibitors, which work to prolong the activity of proteins that boost the release of insulin in response to a rise in blood sugar (i.e., after a meal). It also has an effect on liver output of glycogen. Galvus is another new medication in this class that is poised to follow it, but as of the writing of this article, it is not yet on the market. Fitness professionals will have to stay tuned to the clinical data and the personal experience of their clients with diabetes to know how these newest additions will affect blood sugar management around activity. By now, you can see there is an amazing array of diabetes management tools out there. And diet and exercise are an adjunct therapy for every one.
As a fitness professional, you have an opportunity to assist in empowering your clients with diabetes to make healthy lifestyle choices. Get to know the diabetes educators in your community. Attend a diabetes support group via your local hospital or health center. Take the opportunity to connect with your clients who are living with diabetes by learning to walk in their shoes. Live as a person with diabetes for three days by checking blood sugar levels before and after meals, count every carb you eat and calculate the insulin you would have to take for it. Recognize the potential effects of stress, illness, medications, exercise and activity on blood sugar levels. Then thank your working pancreas for the fabulous job it is doing, minute by minute, every day of your life. Applaud the people with diabetes you know for doing all that they do. Continue to motivate, support and empower them to live healthy, active lives with diabetes.
- American Diabetes Association: Clinical Practice Recommendations 2006. Diabetes Care. Vol 29, January 2006.
- Beaser, Richard & staff. 2001. Joslin’s Diabetes Deskbook – a Guide for Primary Care Providers. Joslin Diabetes Center, Publication Dept, Boston MA.
- Colberg-Ochs, Sheri. 2001. The Diabetic Athlete – Prescriptions for exercise and sports. Champaign, IL: Human Kinetics.