The highs and lows of diabetes and exercise
Issue: Volume 29 Number 1
Diabetes (mellitus) affects an estimated one million Australians, and exercise is considered an integral part of diabetes management. With experience, planning, conditioning, and strategies for managing diet and insulin/medication, a person with uncomplicated diabetes can engage in any type of exercise at any level of intensity - including elite level sport.
Type 1 and type 2 diabetes
Type 1 diabetes affects about 10 to 15 per cent of all people with diabetes. In individuals with this condition, the body is unable to produce insulin required to stimulate glucose uptake from the blood into the body's cells to be used as fuel. In type 1 diabetes insulin injections are needed to control blood sugar levels.
Type 2 diabetes is more common, and very different to type 1 diabetes. People with type 2 diabetes produce insulin but it is ineffective at stimulating glucose uptake from the blood into the cells of the body, due to insulin resistance. In some cases of type 2 diabetes, the body doesn't produce enough insulin to keep the blood glucose levels under control. Although type 2 diabetes can often initially be treated with diet and exercise, many people also require medications to stimulate insulin release and improve insulin sensitivity.
Insulin resistance increases and insulin production decreases with age. Therefore over time, many people with type 2 diabetes may need insulin injections. This does not mean that they have type 1 diabetes, but when considering exercise and its effects in such cases, the same considerations apply to the people with type 1 and type 2 diabetes.
For non-obese people with type 2 diabetes, who control their disease with diet and regular exercise, no additional precautions are required.
People with diabetes are advised to have a full medical check-up before undertaking a new or more strenuous training or exercise program.
Effects of exercise
The long-term benefits of regular exercise for general health and cardiovascular health are well established and do apply to people with diabetes. Specific advantages for people with diabetes include reductions in usual insulin and medication requirements, although glycemic (blood sugar) control does not always improve (Horton 1988).
An insulin-dependent person with diabetes does need to take precautions before, during, and after exercise as there are some risks involved. Exercise increases insulin sensitivity, insulin independent glucose uptake, and glucose usage by muscle. The resulting effects are a greater risk of hypoglycemia in the active person with type 1 diabetes (Camacho et al. 2005).
Regular or planned exercise allows the person with diabetes to learn their own responses to exercise and trial different strategies. Unplanned or intermittent exercise, such as children's activity patterns, increases the risk of Hypoglycemia especially if insulin has already been administered.
Managing type 2 diabetes and exercise
The key components of successful management of type 2 diabetes are to maintain a healthy balanced diet and regular exercise in the same way as a person without diabetes.
The benefits of regular endurance exercise for people with type 2 diabetes are numerous and well supported by the scientific literature for both prevention and treatment of diabetes (American Diabetes Association 2004). There is also evidence that resistance exercise increases insulin sensitivity in people with type 2 diabetes (Horton 1988; American Diabetes Association 2004; Cuff et al. 2003; Dunstan et al. 2002).
The Coaches' Edge archived articles contains a wealth of articles regarding preparation, recovery and hydration for exercise which apply to athletes with Type 2 diabetes.
Managing type 1 diabetes and exercise
The key components of a successful regimen for those with Type 1 diabetes are to:
- reduce the amount of insulin administered prior to exercise
and/ or
- supplement the diet with carbohydrate.
While these are seemingly simple strategies, it is the fine-tuning of these actions that determines success or failure.
What is the difference between hyperglycemia and hypoglycemia?
Hyperglycemia: high blood glucose levels
Hypoglycemia: low blood glucose levels
Hypoglycemia, which leads to fatigue, loss of coordination, mental focus, and reductions in strength, is obviously not compatible with sporting performance. While it may seem reasonable to maintain a state of high blood glucose levels to ensure athletic success the long-term risks are considerable.
While hypoglycemia is a significant risk for people with type 1 diabetes during exercise, exercise-induced hyperglycemia may also occur, particularly if exercise is performed when insulin levels are insufficient. An inadequate level of insulin prevents the uptake of glucose into the exercising muscle cells, leading to high blood sugar levels. A low muscle glycogen level stimulates glucagon to increase liver glucose production, resulting in higher blood sugar levels, while the exercising muscle is unable to use this fuel. Continued exercise under these conditions can increase lipolysis (fat breakdown as an alternative fuel), initiate ketogenesis and dangerously increase blood glucose levels.
High intensity exercise increases the risk of hyperglycemia more than moderate intensity exercise due to the release of counter-regulatory hormones such as adrenaline (Guelfi, Jones and Fournier 2005).
The risk of exercise-induced hyperglycemia can be reduced by:
- avoiding exercise during times of insufficient insulin levels
- avoiding exercise when blood glucose levels are greater than 15mmol/L and ketones are present, and reducing blood sugar levels prior to commencing exercise.
What is the optimal time of day for exercise?
The risk of hypoglycemia during exercise is reduced if circulating insulin levels are low and liver and muscle glycogen stores are topped up. Therefore before breakfast (and morning insulin) - provided a good meal is consumed the night before - or late afternoon (before evening insulin), with regular meals during the day, may be the most appropriate times to exercise. Exercising in the morning is not always possible or practical, and more often sporting activities are held in the afternoon and evening.
However, as mentioned above if insulin is insufficient then hyperglycemia can develop.
What should be done before exercise?
The intensity, duration, and energy requirement of the exercise should be estimated prior to activity.
- Measure blood glucose concentration to determine how well it is under control (Horton 1988; American Diabetes Association 2004):
-
- If blood glucose is <5 mmol/L, extra carbohydrate before exercise is recommended.
- If blood glucose is 5-15 mmol/L, extra carbohydrate may not be required if short exercise duration.
- If blood glucose is >15 mmol/L, delay exercise and measure urine ketones.
- If urine ketones are negative, exercise can be performed, and extra carbohydrate
is not required. - If urine ketones are positive, take insulin and delay exercise until ketones are negative.
- Determine the appropriate pre-exercise carbohydrate meal:
-
- Athletes with diabetes ideally should eat or drink an appropriate carbohydrate-rich snack, meal or fluids one to three hours prior to exercise.
- The pre-exercise meal and fluids should contain about 15 grams of carbohydrate per 30 minutes of anticipated moderate-intensity exercise (for example 30 grams carbohydrate for 60 minutes exercise). The requirements will be higher as intensity increases.
- Carbohydrate Loading will require specific adjustment of insulin dosage to help glycogen storage and should be undertaken with the supervision of a sports dietitian and/ or diabetes specialist (refer to Coaches' Edge archive article, 'Preparing for the long road ahead' for details on carbohydrate loading as a strategy for preparing for endurance events lasting longer than 90 minutes).
- Administer the appropriate pre-exercise insulin dose:
-
- Inject insulin (or adjust the output of an insulin pump) at least one hour before exercise.
- Decrease the dose of insulin so that the peak activity of circulating insulin does not occur during exercise. Short and intermediate insulin doses and pump infusions could be decreased by as much as 50 per cent. Any adjustments should be discussed with a diabetes specialist and be based on careful monitoring and personal experience.
- Do not use an arm or leg that will be involved in exercise as an injection site as exercise increases the effects of the insulin (Kemmer 1992). Be sure that the insulin is injected into subcutaneous tissue not muscle.
- If insulin is administered before unplanned exercise (therefore not adjusted down) then extra carbohydrate should be taken to prevent hypoglycemia. Examples of foods and fluids containing ~15 grams carbohydrate, suitable for before exercise include:
-
- 1 slice bread or 1/2 bread roll
- 1 banana
- 1 1/2 Vita Brits
- 1/2 cereal or sports bar
- 1/2 cup cooked pasta
- 1/3 cup cooked rice
- 1 potato
- 1 glass juice/milk
- 250ml sports drink with the right formulation, such as Gatorade*.
* A properly formulated sports drink contains electrolytes and a 6 per cent carbohydrate level.
What should be done during exercise?
If exercise is prolonged and intense frequent carbohydrate intake is required to prevent low blood sugar levels:
- Monitor blood glucose during long exercise sessions - for running, cycling, swimming, and other endurance type activities, this may require setting a circular course so that glucometres are periodically available.
- Aim to minimise fluid losses during exercise - drink enough to minimise weight loss (but not gain weight) during exercise (refer to Coaches' Edge archive articles, 'There's no room for liquid amber in sport' and 'Drinking on the job - you legend!' for advice on fluid intake and monitoring during exercise).
- If moderate to high intensity exercise is prolonged, use extra carbohydrate feedings during exercise - general carbohydrate requirements based on maximal glucose uptake during exercise are 60-80 grams per hour or ~1 gram per kilogram of body weight per hour (Horton 1988; Riddell et al. 1999).
-
- Drinks that contain rapidly absorbed carbohydrates and electrolytes are excellent in helping to avoid hypoglycemia and plasma volume depletion during exercise (Kremmer 1992).
- A sports drink such as Gatorade is ideal, providing fluid, electrolytes, and 60 grams per litre of rapidly absorbed carbohydrate.
- Other sports drinks with a similar composition (~6 per cent carbohydrate plus electrolytes) may also be effective but have not been studied. Examples of foods and fluids containing ~30 grams of carbohydrate, suitable during exercise, include:
-
- 500ml Gatorade
- 1 cereal bar
- 1 sports bar
- 2 bananas
- 1-2 sports gels
What should be done after exercise?
The recommended principles of recovery such as carbohydrate, protein, and fluid replacement also apply for athletes with type 1 diabetes. During recovery muscle glucose uptake continues to replace muscle glycogen stores. Insulin sensitivity also remains elevated for several hours. Therefore the athlete with type 1 diabetes needs to pay special attention to recovery strategies to avoid delayed hypoglycemia:
- Monitor blood glucose levels, including overnight - this is especially important if exercise is not regular and/or is performed in the afternoon or evening as delayed Hypoglycemia can occur during sleep.
- Reduce insulin dose to decrease the immediate and delayed actions of insulin- this is especially important when exercising in the afternoon or evening. Although low blood glucose can occur several hours after exercise, some insulin is needed after exercise to fully restore muscle glycogen levels.
- Avoid alcohol consumption after exercise - some of the effects of alcohol intoxication are similar to Hypoglycemia or hyperglycemia, and impair the ability to recognise the symptoms of Hypoglycemia. Alcohol also impairs muscle and liver glycogen replacement during recovery (refer to Coaches' Edge archive article, 'Too much booze you lose').
- Ingest ~1.5 grams of carbohydrate per kilogram of body weight soon after exercise to help restore muscle and liver glycogen.
-
- If required, increase carbohydrate intake for up to 24 hours after activity, depending on the intensity and duration of exercise and the risk (based on past experience) of hypoglycemia.
- For athletes undertaking regular training resuming normal carbohydrate-rich eating is appropriate (see below).
- Ingest an appropriate amount of carbohydrate on a daily basis - the type of exercise (endurance, sprint, or resistance), intensity of exercise (high, medium, or low) and duration of exercise (brief, moderate, prolonged, or intermittent) must be considered:
-
- If aerobic exercise of a moderate intensity is to be undertaken on a daily basis and usually lasts less than one hour, the athlete with diabetes should ingest 5-6 grams of carbohydrate per kilogram of body weight on a daily basis.
- If the athlete trains more than 1-2 hours per day, greater than 6-8 grams of carbohydrate per kilogram of body weight may be required daily (refer to Coaches' Edge archive article, 'Carbohydrate: passport to your personal best').
An accredited sports dietitian can help a person with diabetes plan daily meals and snacks to meet individual carbohydrate requirements.
Other practical considerations for the athlete with diabetes
Here are some additional tips for the active person with diabetes:
- Frequent glucose monitoring is essential for safe exercise.
- Always carry some form of rapidly absorbable carbohydrate snack or drink, such as Gatorade.
- Always carry medical identification.
- If convenient, exercise with a friend who knows you have diabetes.
- Carry a mobile phone in case of a diabetic emergency and let people know where you are going.
- Invest in good footgear if walking, jogging, and/or running.
- Take extra care to avoid large fluctuations in blood glucose levels when exercising in the cold or heat.
Summary
An athlete with diabetes should:
- decrease insulin dose prior to exercise and avoid injecting into the exercising limb
- consume enough carbohydrate prior to and during exercise to meet fuel requirements and maintain blood sugar levels
- avoid exercise when blood glucose levels are greater than 15mmol/L and ketones are present
- consume appropriate amounts of fluid before, during, and after exercise
- decrease insulin dose after exercise and continue to consume carbohydrate-rich foods to avoid delayed hypoglycemia
- have some form of rapidly-absorbed carbohydrate readily available for treatment of hypoglycemia
- consult a sports dietitian and/or diabetes specialist for personal advice on managing diabetes and exercise.
Additional Information
Sports Dietitians Australia: www.sportsdietitians.com
Diabetes Australia: www.diabetesaustralia.com.au
References
American Diabetes Association 2004. 'Position statement: Physical activity/exercise and diabetes', Diabetes Care, 27:S58-62.
Camacho, RC, Galassetti, P, Davis, SN and Wasserman, DH 2005. 'Glucoregulation during and after exercise in health and insulin-dependent diabetes', Exercise and Sport Science Reviews, 33(1):17-23.
Cuff, DJ, Meneilly, GS, MArtin, A, Ignaszewski, A, Tildesley, HD and Frohlich, JJ 2003. 'Effective exercise modality to reduce insulin resistance in women with type 2 diabetes', Diabetes Care, 26(11):2977-82.
Dunstan, DW, Daly, RM, Owen, N, Jolley, D, DeCourten, M, Shaw, J and Zimmet, P 2002. 'High-intensity resistance training improves glycemic control in older patients with Type 2 Diabetes', Diabetes Care, 25(10): 1729.
Guelfi, KJ, Jones, TW and Fournier, PA 2005. 'The decline in blood glucose levels is less with intermittent high-intensity compared with moderate exercise in individuals with Type 1 diabetes', Diabetes Care, 28:1289-94.
Horton, ES 1988. 'Role and management of exercise in diabetes mellitus', Diabetes Care, 11(2):201-11.
Kemmer, FW 1992. 'Prevention of hypoglycemia during exercise in Type 1 diabetes', Diabetes Care, 15(suppl.4): 1732-5.
Riddell, MC, Bar-Or,O, Ayub, BV, Calvert, RE and Heigenhauser, GJF 1999. 'Glucose ingestion matched with total carbohydrate utilization attenuates hypoglycemia during exercise in adolescents with IDDM', International Journal of Sports Nutrition, 9:24-34.
This article was adapted by Anthony Meade from Peter A Farrell, 2003. 'Diabetes, exercise and competitive sports', Sports Science Exchange 90, 16 (3), accessed at www.gssiweb.com
This article is reproduced with the permission of the editorial team at Coaches' Edge, a free web-based newsletter that publishes the latest research in hydration, nutrition, training, injury management, and mental preparation among others. To join Coaches' Edge log on to www.coachesedge.com.au.
