Type 1 diabetes
For athletes living with type 1 diabetes, the cells of the pancreas that make insulin are destroyed which means no insulin is being made to regulate blood glucose levels. Blood sugar (or glucose) cannot enter the cells of the body for energy causing blood glucose to build up in the blood. Athletes living with type 1 diabetes require daily injections of insulin to help keep them alive, manage their blood glucose levels and prevent/ delay diabetes related complications.
Effects of exercise on blood glucose levels
Aerobic sports such as marathons, triathlons and road cycling and swimming tend to reduce blood glucose levels.
Anaerobic sports such as weightlifting/ powerlifting, crossfit, 100 & 200 m sprinting and boxing tend to increase blood glucose levels.
Mixed sports (team sports) like AFL football, rugby, soccer, netball, basketball tend to stabilise blood glucose levels during exercise but then drop in the hours after exercise.
In addition to the type of exercise, it is important to think about the duration and intensity of the exercise session and the insulin conditions prior to exercise such as the type of insulin (basal or bolus), timing of injection and, the amount circulating in the blood will all play a role in what your blood glucose levels are doing around exercise.
You should work closely with your diabetes healthcare team including an Accredited Sports Dietitian and Credentialled Diabetes Educator (CDE) when learning how your body responds to exercise.
Blood glucose targets before and during exercise
Blood glucose target before starting and during exercise should be individualised to the person living with type 1 diabetes. However, for aerobic exercise lasting ~60 minutes a range of 7-10 mmol/L has been suggested to balance performance and reduce the risk of going low.
A healthy diet with good food variety matched with insulin and regular exercise is important for diabetes management. Good diabetes management should remain top priority and accurate carbohydrate counting matched to insulin should be mastered before applying sports nutrition principles.
Eating regular, low GI meals with adequate protein, healthy fats and colourful non-starchy vegetables in appropriate portions can help keep blood glucose levels consistent and stable. This will also ensure all nutrients are consumed to maintain health, performance and recovery.
Examples of low GI foods include: apples, pears, sweet potato, sweet corn, rolled oats, pasta, basmati rice, lentils, kidney beans, milk and yoghurt.
High GI foods can be useful in situations where low GI meals/ snacks are not practical such as within the hour(s) before and during exercise.
Examples of high GI foods include: white bread, scones, crumpets, jasmine rice, rice cakes, jelly beans and other confectionery.
Sports foods such as energy gels/ bars, sports drinks, sports lollies, liquid meal substitutes such as Sustagen Sport can also be suitable options.
It is important to remember that the total carbohydrate (both starches and sugars) will have the most direct impact on blood glucose levels. This needs to be considered for appropriate insulin dosing to prevent fluctuations in blood glucose levels.
New research has also shown that protein and fat can also affect how blood glucose responds after a meal. Adjustments to insulin dose and delivery may be needed.
Speak with your diabetes educator (CDE) or Endocrinologist for more information.
Pre-exercise meal & snack
In general, a pre-exercise meal consumed 2-4 hours prior to exercise should contain low GI carbohydrates, some protein and adequate fluid for hydration. Together with appropriate insulin dose and delivery, will result in more stable blood glucose levels prior to exercise.
A high GI carbohydrate containing snack may need to be consumed prior to commencing exercise depending on the trend in blood glucose leading into the exercise session.
Regular monitoring of blood glucose levels in the hours before exercise can help you make decisions about food and insulin adjustments to maintain stable and safe blood glucose levels.
Consuming carbohydrate is generally not needed when exercise is less than 30 minutes duration. Blood glucose levels will start to fall when aerobic exercise goes beyond 60 minutes.
To prevent going low and/ or improve exercise performance, you should aim to consume small amounts of carbohydrate every hour during exercise greater than 60 minutes duration.
Recovery nutrition after exercise
The goals for the post-exercise meal should be to replenish used stores of carbohydrate, repair damaged muscles (protein) and rehydrate (water) to restore fluids lost from sweating during exercise.
After a single bout of moderate intensity exercise, the body is super sensitive to insulin which can last up to 2 days. For those exercising daily, this may mean a reduction in the amount of daily insulin required as exercise reduces blood glucose levels without the need for insulin.
Nevertheless, for athletes living with type 1 diabetes, consuming a low GI mixed meal or snack with protein in the hour after exercise followed up by dinner a couple of hours later will promote muscle recovery and reduce the risk of going low post-exercise.
A supper or pre-bed snack such as fruit and yoghurt might also help prevent going low overnight. Particularly if exercise is undertaken in the afternoon or evening.
It is recommended that you work with an Accredited Sports Dietitian with experience in type 1 diabetes, exercise and nutrition to work out the right amount of carbohydrate for your needs.
Adjustments to basal (long-acting) and bolus (short-acting) insulin or both will be needed around exercise to prevent going too high or too low.
A CDE or Endocrinologist can assist you further with understanding the effects of insulin around exercise.
Monitoring of blood glucose levels
There are a variety of tools and technology out there to help athletes monitor their blood glucose levels. Work with your diabetes healthcare team to find one that suits your individual needs and budget.
Blood glucose monitoring is essential before, during and after exercise to understand what your blood glucose response to exercise is and tell you what you need to do next to maintain stable and safe blood glucose levels.
Hypo (hypoglycemia) kit
It is vital that athletes living with type 1 diabetes carry a hypo kit with them at all times. A hypo occurs when blood glucose levels fall below 4.0 mmol/L.
Symptoms of a hypo can include:
- Weakness, trembling, shaking
- Lightheadedness or dizziness
- Difficulty concentrating
- Blurred vision
If you experience any of these symptoms, follow these 3 steps:
Step 1: Check your blood glucose levels. If ≤ 4.0 mmol/L, treat quickly as untreated hypos can be dangerous.
Step 2: Have 15 g of rapid acting carbohydrates such as:
- Glucose tablets equal to 15 g carbohydrate
- 6-7 regular jelly beans (4 large glucose jelly beans)
- 125mL (1/2 glass) of orange juice or regular soft drink (i.e. Coca Cola)
- 3 teaspoons of sugar or honey
Step 3: Wait 15 minutes and re-check blood glucose levels. If still < 4.0 mmol/L, repeat Step 2, if > 4.0 mmol/L, eat some low GI carbohydrate foods:
- 250mL glass of plain milk/ soy drink
- 1 slice of whole-grain bread with spread of choice
- 1 tub of fruit flavoured yoghurt
- 1 muesli bar
For individualised advice on hypo treatment, speak with your doctor or diabetes healthcare professional.
Junior Diabetes Research Foundation www.jdrf.org.au
National Diabetes Organisation www.diabetesaustralia.com.au
National Diabetes Services Scheme www.ndss.com.au
State and Territory Diabetes Organisations
NSW & ACT www.diabetesnsw.com.au
Australian Diabetes Educators Association www.adea.com.au
Dietitians Association of Australia www.daa.asn.au
Sports Dietitians Australia www.sportsdietitians.com.au