Diabetes is a group of metabolic diseases where the pancreas either does not produce adequate insulin or the body does not properly respond to the insulin, resulting in high blood glucose levels over a prolonged period. Diabetes is a global epidemic, and racial/ethnic minorities are affected disproportionately. In 2011, 365 million people worldwide had a diagnosis of diabetes (1). The West Pacific region had the highest number of individuals (131.9 million) diagnosed with diabetes. The Middle East and North Africa regions had the highest prevalence rates of diabetes at 11.0%. The North America/Caribbean region had the second highest prevalence rate of diabetes at 10.7%. South-Central America and Southeast Asia had similar diabetes prevalence rates of 9.2%, whereas Europe had a 6.7% prevalence rate. Africa has the lowest prevalence rate of diabetes at 4.5%; however, Africa also had the highest proportion of undiagnosed diabetes, with at least 78% of affected individuals being undiagnosed (2). It is estimated that 9.3% of the U.S. population, or 29.1 million (21.0 million diagnosed, 8.1 million undiagnosed), are affected by diabetes. Among those aged 20 or older, 7.6% of individuals with diabetes are non-Hispanic white, 9.0% are Asian American, 12.8% are Hispanic, 13.2% are non-Hispanic black, and 15.0% are American Indian/Alaska Native (3).
It is widely known that prevention of a disease before it is diagnosed is preferred and can reduce costs associated with health care (4). Furthermore, a person’s lifestyle, including physical activity and dietary patterns, can influence the onset and progression of chronic disease. Increased physical activity and improved nutrition also is a practical strategy for reducing the risk of diabetes, and even those individuals already diagnosed with type 2 diabetes (T2D) could benefit from a lifestyle modification program (5). Individuals with diabetes can realize the same benefits of physical activity as those without diabetes, including increased energy, normalization of blood glucose, and a reduction of chronic disease risk factors. However, persons with diabetes, and those who supervise clients who have diabetes, should be aware of exercise recommendations and contraindications. This article outlines special physical activity and nutritional considerations for those with type 1 diabetes (T1D) and T2D.
TYPE 1 DIABETES
T1D can occur at any age but is most commonly diagnosed between infancy and the late 30s. T1D results when the pancreas produces little to no insulin, due to the body’s immune system’s destruction of the insulin-producing cells in the pancreas. This process results in lifelong dependence on exogenous insulin (6). In the SEARCH for Diabetes in Youth study, it was estimated that 18,436 U.S. youths were newly diagnosed with T1D in 2009 (Figure 1) (7). Worldwide, approximately 78,000 youths are diagnosed with T1D annually. Incidence varies among countries: East Asians and American Indians have the lowest incidence rates (0.1–8 per 100,000/year) as compared with the Finnish, who have the highest rates (>64.2 per 100,000/year) (8). In the United States, the number of youth with T1D was estimated to be 166,984 (9).
Exercise and Nutrition
Benefits of Exercise
Many benefits can be gained from regular exercise or physical activity, such as better mood, higher quality sleep, and improving various cardiovascular risk factors such as cholesterol and triglycerides. There are some other specific advantages for people with T1D:
- Exercise can improve overall and disease-specific quality of life (10).
- Regular activity may enhance or improve insulin sensitivity (6).
- Exercise contributes to an increased metabolism, which plays a role in the regulation of body weight.
- Physical activity lowers blood pressure and heart rate at rest and during submaximal exercise.
- Increases self-efficacy for maintaining normal blood glucose levels by learning about the short- and long-term benefits of optimal control and how to manage blood glucose before, during, and after exercise (6).
Individuals with T1D should follow general recommendations for aerobic and resistance training while ensuring that he or she manages his or her blood glucose levels before, during, and after the exercise session. Practical recommendations for frequency, intensity, duration, mode, and rate of progression for exercise are listed in the T2D section. Any patient with T1D should seek help from his or her health care team if problems managing blood glucose levels occur.
Hydration is essential for thermoregulation and cardiovascular function in active individuals but is particularly important for people with T1D to help maintain optimal blood sugar levels (11). Dehydration slows down food absorption and raises blood glucose rapidly. In addition to regular fluid consumption during the day, we recommend your clients drink 20 oz of extra fluid an hour or two before starting exercise and 28 to 40 oz of fluid for every 1 hour of exercise or activity. Both male and female adolescent athletes who engage in sports that require muscular strength (e.g., football, wrestling) may consider increasing protein intake or taking performance-related nutritional supplements. We recommend lean meats (e.g., chicken breast, fish) as primary sources of protein. The long-term and short-term effects of creatine, a popular supplement taken to improve strength in adults, are still an understudied area in children and adolescents. The American College of Sports Medicine and the American Academy of Pediatrics both recommend against the use of creatine supplements in those younger than 18 years, and we adhere to that recommendation among our patients (12). Poorly controlled T1D increases the risk for renal complications with resulting proteinuria. Although physical activity can acutely increase urinary protein filtration, there is currently no evidence that vigorous activity increases the progression rate of diabetes-related kidney disease and no specific contraindication to exercise per se in diabetes-related kidney disease. However, those patients with diabetes and microalbuminuria (mild to moderate levels of albumin in the urine), macroalbuminuria (severe levels of albumin in the urine), renal failure, or other risk for renal problems should NOT markedly increase protein supplementation without consulting with his or her health care provider and should maintain the recommended dietary allowance of 0.8 g of protein per kilogram of body weight (13).
Hydration is essential for thermoregulation and cardiovascular function in active individuals but is particularly important for people with T1D to help maintain optimal blood sugar levels (11).
Treatment — Controlling Blood Glucose Levels
Preventing hypoglycemia is of primary importance with the active T1D client. Because he or she is on insulin, he or she is at greater risk for hypoglycemia during exercise and for delayed onset hypoglycemia after prolonged aerobic (≥60 minutes) or anaerobic exercise. These individuals should check blood glucose before, during, and after exercise. Blood glucose levels before activity should not be 100 mg/dL or less or 250 mg/dL or greater. Blood glucose management varies depending on age and type of activity. A recommendation from the American Diabetes Association (ADA), which is similar to most organizations, includes checking blood glucose at least 30 minutes before exercise. If preexercise blood glucose is 100 mg/dL or less, the client would benefit from a 15- to 30-g high glycemic index carbohydrate snack like fruit juice, fruit, or even glucose tablets. If preexercise blood glucose is 250 mg/dL or greater, caution is recommended, and the client should be checked for the presence of ketones. If ketones are present, exercise is contraindicated until ketone levels are no longer present to prevent the development of diabetic ketoacidosis. Premeal insulin doses also may need to be adjusted depending on the duration and mode of exercise to prevent exercise-induced hypoglycemia. For moderate level of exercise (e.g., walking, bicycling leisurely, shooting basketball, mowing the lawn), your client should be careful to avoid acute hypoglycemia that can occur during or after exercise. For more intensive and longer activities (e.g., jogging, bicycle race, basketball game), increased carbohydrates may be necessary and more care taken to prevent delayed hypoglycemia, which can occur later in the night or the next day. Blood glucose should be monitored immediately after exercise and one to two times for 2 to 3 hours after exercise, especially if the exercise bout is 60 minutes or more. In these situations, your clients may benefit from reduction in basal insulin of 20% to 25% and a lower glycemic index snack like yogurt, peanut butter, or dark chocolate before bedtime. Clients with diabetes should determine the appropriate food intake based on blood glucose levels before, during, and after exercise by keeping records of activities and blood glucose levels.
Practical Strategies — Sprinting to Reduce Hypoglycemia
To prevent delayed hypoglycemia, a practical strategy for your clients may be to perform a hard sprint for 10 seconds after exercising. This strategy may be physiologically explained through an increase in catecholamine and lactate levels. Elevated catecholamine levels stimulate hepatic glucose production through glycogenolysis, which inhibits insulin-mediated glucose uptake by the skeletal muscle and stabilizes blood glucose levels in patients with T1D. Likewise, elevated lactate levels caused by sprinting can help stabilize blood glucose through gluconeogenesis via the Cori Cycle (14). Furthermore, sprinting before a moderate intensity exercise session could have some benefit in the stabilization of glycemia (15), but care should be taken when engaging in a sprint before moderate intensity exercise unless a proper warm-up is completed. Sprinting should only be considered an option for clients who are in good health and do not have any contraindications to high-intensity exercise. Each individual with T1D should continue to monitor glycemia levels and make adjustments as needed. If your client with diabetes is having chronic lows or highs, he or she may need to alter his or her insulin dose or make changes to his or her meal plan in consultation with his or her physician or endocrinologist. The health care team can use blood glucose and activity information to suggest adjustments and refine the care plan.
Health Impact and Other Important Considerations
Individuals with T1D can exercise safely and effectively and gain the same benefits from exercise as anyone else. However, he or she should pay more attention to how his or her body responds to exercise; learn to balance insulin, food, and physical activity; and use evidence-based strategies to minimize the risk of hypoglycemia during and after exercise. Lastly, there are several important considerations for the active client with T1D who is vigilant about blood glucose control. These individuals should always carry the following items with him or her, especially when he or she exercises:
- Fast-acting carbohydrate to treat low blood glucose level
- Additional snacks such as cheese and crackers or a sandwich
- A bottle of water to maintain adequate hydration
- Glucose meter and supplies
- Medical alert identification (e.g., medical bracelet)
It is recommended that your client always has a friend, coach, or some other adult nearby who is able to identify and respond to low blood glucose levels. If your client’s blood glucose levels are high before exercise, remind him or her to check his or her blood or urine for ketones. If your client tests positive for ketones, avoid activity and treat the elevated blood glucose and ketones as instructed by your health care team. A child or adult should NEVER exercise if his or her blood glucose is 250 mg/dL or higher and ketones are present. This puts him or her at risk for developing diabetic ketoacidosis.
TYPE 2 DIABETES
With an estimated 22 million Americans living with diabetes and an even greater number with prediabetes, it is essential that researchers and clinicians make prevention and treatment of T2D a priority. T2D is caused by the inability of muscle and other tissue cells to properly respond to insulin, called insulin resistance, and/or inadequate compensatory insulin secretion. T2D is more prevalent than T1D and represents 90% to 95% of all diabetes cases. The risk for developing T2D increases with age, obesity, and physical inactivity (16). Diabetes can be diagnosed from any one of four criteria (Figure 2) including a glycated hemoglobin (A1c) value higher than 6.5%, fasting plasma glucose 126 mg/dL or higher, 2-hour plasma glucose 200 mg/dL or higher during an oral glucose test, or symptoms of hyperglycemia (16).
Exercise and Nutrition
Benefits of Exercise
Similar benefits found in T1D also can be seen for those individuals with T2D. In addition to the benefits mentioned earlier, such as better mood, higher quality sleep, and improving cardiovascular risk factors, patients with type 2 diabetes also experience better control of blood glucose and modest weight loss, two factors that can help reverse the signs, symptoms, and even diagnosis of T2D. Benefits of physical activity in T2D can be achieved through a few basic exercise guidelines that establish the frequency, intensity, duration, mode, and rate of progression for aerobic and resistance training (6,10).
- Frequency: Start with a minimum of 3 d/wk of moderate intensity exercise and no more than 2 consecutive days between exercise sessions because of the short duration of improvements in insulin function. The recommended amount of aerobic exercise for the general population is 5 d/wk of moderate intensity or 3 d/wk of vigorous intensity (6,10).
- Intensity: Moderate intensity is between 40% and 60% Heart Rate Reserve, which is similar to brisk walking in most clients with T2D. Additional benefits can be seen by engaging in vigorous intensity exercise of greater than 60% Heart Rate Reserve.
- Duration: Moderate intensity exercise for at least 150 min/wk. This exercise does not need to be continuous and can be accumulated in 10-minute bouts.
- Mode: A variety of types of aerobic exercise that use large muscle groups (i.e., swimming, cycling, walking, running, rowing).
- Rate of Progression: A gradual progression of not more than a 10% increase per week in exercise intensity or duration to minimize the risk of injury and to promote exercise adherence is recommended (6,10).
- Frequency: 2 or 3 nonconsecutive days each week with a minimum of 48 to 72 hours of rest in between each resistance training session targeting a given muscle group.
- Intensity: Training should be moderate or vigorous for optimal improvements in strength and insulin action. Moderate intensity begins at 50% of an individual’s one repetition maximum (1RM) and vigorous intensity at 75% to 80% of the 1RM.
- Duration: The training session should consist of 5 to 10 exercises and 10 to 15 repetitions that use all the large muscle groups in the upper body, lower body, and core. It is recommended to complete 1 to 4 sets for each exercise.
- Mode: Resistance machines and free weights should be the primary mode of resistance training. Other types of resistance training using bands, cables, body weight, etc., may be used. In addition, functional movement exercises that allow the client to simulate activities of daily living (e.g., walking, climbing stairs) and instrumental activities of daily living (e.g., cooking, doing housework) should be a focus to improve disease-specific and overall quality of life.
- Rate of Progression: Rate of progression should be slow and only take place when the number of repetitions per set can consistently be exceeded. A common rule is the 2-for-2 rule, stating that weight increases should occur if the individual can perform 2 more repetitions on his or her final set in 2 consecutive resistance training sessions. Progression of resistance training to three weekly sessions using three sets of 8 to 12 repetitions at 75% to 80% 1RM should be the optimal goal for strength gains. Recovery periods between strength sets will vary based on individual resistance training goals (i.e., hypertrophy, maximal strength or power, and endurance), usually ranging from 30 seconds for endurance to 3 or more minutes for maximal strength and power (6,10).
Children with either T1D or T2D should be encouraged to engage in at least 60 min/d of moderate to vigorous aerobic physical activity and at least 3 d/wk of muscle and bone strengthening activities (17). Vigorous intensity aerobic and resistance training in children and adults should be used with caution, and the clinician should ensure that the client has no contraindications to vigorous intensity exercise.
Although there is not a one-size-fits-all food plan that is suitable for each individual with diabetes, it is important that each person works with a registered dietitian and health care team to establish eating patterns that will manage both glycemic levels and weight. Diets in overweight or obese persons with T2D should focus on modest weight loss ranging from 5% to 7% of initial body weight. These diets should primarily consist of nutrient-dense foods (i.e., fruits, vegetables, whole grains, and lean meats) while achieving the desired energy deficit. Average protein intake should be 0.8 g/kg of body weight per day and may increase slightly if higher levels of physical activity are being achieved. Supplements for Omega-3 fatty acids, vitamins, or minerals have little supporting evidence for outcome improvement in patients with T2D who do not have a dietary deficiency. It is recommended that a registered dietitian be consulted before supplementation is added (10). Furthermore, patients with T2D and hyperglycemic hyperosmolar state (HHS), a complication of diabetes in which high blood sugars cause severe dehydration, need to pay particular attention to water intake and fluid management. HHS, characterized by a serum glucose greater than 600 mg/dL, a serum osmolality greater than 330 mOsm/kg, and no significant ketosis or acidosis can be avoided through proper blood glucose management (6). The classical symptoms for hyperglycemia may include polyuria (frequent urination), polydipsia (increased thirst), polyphagia (increased hunger), and weight loss (16).
Treatment — Controlling Blood Glucose Levels
Several agencies have published clinical guidelines reviewing recommendations for exercise in patients with diabetes including the ADA, the American Association of Clinical Endocrinologists, and the American Association of Diabetes Educators. In general, it is recommended that persons with diabetes should receive medical care from a multidisciplinary, collaborative team with expertise in diabetes management to include physicians, physician assistants, nurse practitioners, dietitians, exercise specialists, mental health providers, dentists, podiatrists, and pharmacists. The patient should work with his or her team to develop an individualized treatment plan for diabetes self-management and set treatment goals for all aspects of his or her diabetes care. Physical activity and exercise have been shown to improve glycemic control, lower cardiovascular risk factors, promote weight loss, and improve overall health, but its role in reducing diabetes-related complications is not fully understood (10,16). Patients may see a clinically significant reduction in A1c with regular exercise independent of changes in body mass index (BMI).
Practical Strategies — Prevention Before Diagnosis
Although there may be some drug treatments that have been successful in reducing the risk of diabetes, lifestyle intervention and behavior change have been shown to be among the most effective methods for reducing T2D risk. An article published in the New England Journal of Medicine compared drug treatment, specifically metformin, and lifestyle intervention in a group of 3,234 adults who had prediabetes and had an average BMI of 34 ± 6.7 kg/m2. Researchers found that participants assigned to the lifestyle modification group had greater body weight loss and physical activity increases than those who were assigned to the drug treatment or placebo groups. The incidence of diabetes was 58% and 31% lower in the lifestyle intervention and drug treatment group, respectively, when compared with the placebo (5). In addition, the incidence of diabetes was reduced by 39% in the lifestyle intervention when compared with the drug treatment group.
Supplementary practical strategies can be seen in Figure 3 and can be used as a guide to developing individualized plans for your client. Lifestyle interventions should include a combination of diet, physical activity, and behavioral therapy techniques with the main goals of increasing physical activity and reducing body weight. Using dietary restriction of fat often is a successful strategy for weight loss in patients with T2D because of the higher caloric density of fat (9 kcal/g) when compared with carbohydrates or protein (4 kcal/g) (10). A reduction in dietary fat intake also decreases low-density lipoprotein cholesterol, which is associated with a higher risk for future cardiovascular events.
A complete assessment of your client’s exercise history and motivational level also are necessary steps to facilitating behavior change through lifestyle modification. Through an assessment of exercise history and motivational levels, you may learn potential barriers that will limit your client’s ability or readiness to make changes. These barriers could include, but are not limited to, a physical injury that required surgery, an emotional or social limitation such as lack of support from family and friends, financial and work-related stress, or problems with time management. Being aware of roadblocks will help you individualize a plan for your client that works on moving past these barriers and shifting his or her focus to the benefits that may come from these lifestyle changes. Working past these barriers may be challenging, which is why we recommend treating each client individually and offering encouragement in ways that fit his or her motivational level and readiness to change. Behavior change theories, such as the health belief model and transtheoretical model (also called stages of change), offer constructs that may directly or indirectly influence how successful your client will be in his or her weight loss journey and lifestyle modification program (18,19). We recommend you familiarize yourself with various behavior change theories, although application of those theories and specific recommendations for adapting the theories to fit an intervention for your client are beyond the scope of this article.
Health Impact and Other Important Considerations
Exercise and healthy eating have both acute and long-term effects on the management of diabetes. A combination of resistance and aerobic training generally is best for patients with diabetes and should be an individualized and progressive program. Although using both aerobic and resistance exercise training is recommended and more likely to cause improvements in blood glucose control, additional research is needed to determine whether caloric expenditure, exercise duration, or mode is most responsible (16). Health and fitness professionals should use these recommendations as a guide for working with clients who have diabetes, while paying careful attention to monitoring how the client is feeling and where his or her blood glucose levels are before, during, and after exercise.
BRIDGING THE GAP
Diabetes is a worldwide epidemic. Persons with diabetes should regularly engage in physical activity and healthy nutritional practices so he or she can gain the same health benefits as those without the diagnosis. It is important for those with diabetes and those who supervise individuals with diabetes to be aware of disease-specific recommendations and contraindications. In this article, we provide evidence-based recommendations for those with T1D and T2D.
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