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Sports nutrition and Type 1 diabetes

Why is regular exercise good for diabetes?

Hopefully, you're already aware of how exercise can have a positive impact on your diabetes management, as well as your general wellbeing. If not, here are just a few of the benefits of building regular exercise into your routine:

  • a decrease in certain blood lipids – and an increase in beneficial cholesterol
  • a decrease in blood pressure
  • a positive effect on mood
  • as a stress reliever, especially when performed in nature
  • improvement in sleep quality

...and there's more

From the point of view of day-to-day diabetes management, one of the most important benefits of exercise is that it increases insulin sensitivity.

As a result, this translates to needing less insulin for the same amount of carbohydrate, and it can also dampen post-meal blood sugar spikes. The insulin sensitivity effect of aerobic exercise usually starts to decline within 1–2 days.

Therefore, regular aerobic activity is essential to keeping the body in an insulin-sensitive state.

At times, it can feel like a mental workout before you’ve even started exercising: deciding if and how much you need to eat before and during exercise, in addition to deciding what to do with insulin before, during and after exercise.

We will be discussing the various factors to consider when making these decisions in order to help you manage your diabetes during exercise.

Exercising almost daily (in contrast to exercising only twice a week) will ensure that you remain in a more insulin-sensitive state most of the time, instead of having varying levels of insulin sensitivity from one day to the next.

This should translate to less variability in blood glucose and make it easier to manage your diabetes.

The challenge of managing diabetes during exercise

What are the challenges?

  • The risk of hypoglycaemia is high

    In a person who doesn't have Type 1, there’s a reduction in insulin production during aerobic exercise. Because a person with Type 1 diabetes doesn’t produce their own insulin, unless adjustments are made to the amount of insulin injected prior to exercise, then circulating levels of insulin will be the same as if they weren’t doing exercise. This can lead to a hypo as more glucose is being taken into the muscles.
  • Competition stress can be a real challenge

    People with Type 1 often battle with high blood glucose levels before and during competition events, due to the release of stress hormones. Here, as insulin is constant, it can be too low to combat the temporary rise in stress hormones from the competition.
  • Different types of exercise have different effects on blood glucose

    We can divide exercise into three broad categories:
    1. Anaerobic: high-intensity and short-duration exercise
    2. 'Stop, start' exercise: aerobic exercise interspersed with bursts of high-intensity exercise
    3. Aerobic: longer-duration and lower-intensity exercise

Examples of different types of exercise within these categories.

The arrow below illustrates how various types of exercise may impact blood glucose levels during exercise. Knowing how your blood glucose responses to different types of sports and different types of training sessions (within the same sport), can help decide what is a safe starting blood glucose and how much carbohydrate may be needed during exercise.

What are the challenges?

Exercising when you have 'insulin on board' (IOB) – for example, when you exercise soon after a meal and still have some rapid insulin in your system – may result in a greater risk of hypoglycaemia and a greater need for carbohydrate to offset the IOB. This variable means that doing the same exercise, but at different times, can result in varying effects on blood glucose. It’s essential to know how much IOB you have at the start of exercise.

Studies show that there is a large variation in how subjects respond to exercise. What this means is that guidelines are very useful, as well as learning from others, but remember that you’re an individual and your body may respond differently to another.

Learn how different types of sports or training sessions affect your blood glucose by testing before, during and after exercise, keeping a detailed record to refer back to. Remember, you're an individual so don't be alarmed if your blood glucose level behaves differently to what you expected.

Optimal blood glucose levels before and during exercise

Fear of hypos often results in exercising with higher-than-optimal blood glucose levels. Below is a guideline to indicate blood glucose levels before and during exercise. Monitoring levels is key to managing your diabetes and exercise successfully, and in order to get the most out of your workout.

Before exercise: safe starting blood glucose levels

See the table below for guidance on blood glucose levels before exercise, and the required actions.

Starting blood glucose

Recommendations (note: a rule of thumb)

Less then 5mmol/L
  • Ingest 10-20g of glucose before exercise
  • Delay exercise until blood glucose is above 5mmol/L
5–8 mmol/L
  • Ingest 10g of glucose before exercise
  • Exercise can be started
  • Low-intensity exercise can be started
Greater than 15mmol/L
  • Check blood ketones
  • If no ketones, perform low-intensity exercise and/or give small correction dose of insulin
  • If ketones less than 1.0mmol/L, consider small correction dose of insulin and perform low-intensity exercise and monitor blood glucose
  • If ketones between 1–1.4mmol/L, take correction dose and exercise after 1 hour and monitor blood glucose
  • If blood ketones above 1.5mmol/L, follow regular guidance received from diabetes team for treating ketones

Noting points

  • People with Type 1 diabetes should aim to start exercise with a blood glucose between 5–8 mmol/L. If this seems too low, over time, gradually lower your starting blood glucose and bear in mind that you can ‘top up’ with carbohydrate during exercise.
  • The above recommendations apply to approximately 10 minutes before exercise.
  • Adapt recommendations to suit your individual blood glucose response to exercise and consider the type of exercise. For example, those doing high-intensity exercise may feel safer starting with a blood glucose of 5mmol/L, while those doing longer-duration, endurance exercise may feel safer starting on a blood glucose of 8mmol/L.
  • If using continuous glucose monitoring (CGM) take the trend arrow into consideration and adapt the recommendations. For example, a blood glucose of 6mmol/L with one or two vertical arrows going up may not require a snack.
  • The best snacks to choose before exercise are fast-acting carbohydrate snacks. These are the usual hypo treatment options such as dextrose tablets, fruit juice etc.

During exercise: blood glucose levels

Research has shown that blood glucose in the range of 5–8 mmol/L is required to maximise performance during exercise. There are obvious consequences of going low during exercise and this is often on the mind of most people with Type 1 diabetes, which is understandable. Exercising with high blood glucose levels will also negatively affect performance, and can lead to fatigue, lack of mental sharpness and agility, and dehydration.

A single blood glucose test can be misleading, as it doesn’t show which way the blood glucose is trending. Before exercise, consider taking two blood glucose tests in short succession if you expect your blood glucose to be in flux.

Exercising with blood glucose in the suggested ranges will allow your body to burn more fat during exercise, while preserving muscle glycogen stores. But, be aware that if exercising with high blood glucose, it’s important to increase your usual fluid intake during exercise.

Sports nutrition and exercise with Type 1 diabetes

Fuelling for exercise

Having low amounts of IOB at the start of exercise has certain benefits. These include being able to use more of your fat stores during exercise (therefore allowing you to preserve your glycogen stores), less risk of hypoglycaemia and less carbohydrate needed during exercise to maintain blood glucose.

When preparing for a training session, aim to have little IOB during exercise, especially if you’re concerned about going low and/or don’t want to have to take onboard carbohydrate to offset the IOB.

This means giving thought to the timing of meals and insulin boluses in relation to the timing of exercise, and also giving thought to pre-exercise meals.

All pumps will display the IOB – note that this is only reflecting the bolus insulin and not the basal rate or long-acting insulin.

If on multiple daily injections (MDI), use an app which tracks active insulin or glucometers with bolus calculators.

Meal timing options

Eating three hours before a training session

The action of most rapid-acting insulins is 3–4 hours, which means that an insulin bolus taken three hours before a training session will have little impact on the session. In this scenario, take your usual meal bolus and eat normally.

Ideally, most of the carbohydrate in the meal should be minimally processed and low glycaemic – examples of good choices include jumbo or steel-cut oats, oat and nut muesli, root vegetables such as boiled potatoes or sweet potato, wholegrains such as quinoa, brown rice and bulgur wheat.

Eating two hours before a training session

Eating two hours before the session is long enough to allow you to take your usual insulin bolus, but at the same time is short enough so that you will still have some IOB at the start of the session. Reducing your meal insulin bolus at this time will likely result in a higher-than-desired post-meal blood glucose and therefore may not be a good strategy.

Consider having a low-glycaemic carbohydrate meal with a moderate amount of carbohydrate – this will ensure that the insulin bolus is not too large, which means less IOB during exercise. The meal should also have a moderate amount of fat, as too much fat at this time can delay the absorption of carbohydrate into the stomach.

In this scenario, you will have IOB when starting exercise and therefore may want to consider reducing your insulin basal rate (if using an insulin pump) at least an hour before starting exercise.

Eating 60–90 minutes before a training session

  • To eliminate the need for a bolus and therefore no IOB during exercise (other than basal insulin), eat a non-carbohydrate meal/snack containing protein and healthy fats. For example, egg, ham, tuna, cheese, avocado, seeds or nuts and vegetables such as leafy greens.
  • Another option is to have a small amount of low-glycaemic carbohydrate with a source of protein and fat (ideally not much more than 30g carbohydrate), with a reduced insulin bolus. If it is a higher-intensity session and you require carbohydrate to fuel the exercise, then supplement with a reasonable amount of high-glycaemic carbohydrate (e.g. energy drink and gels) during the session, and refuel with carbohydrate after the session to make up for the lack of carbohydrate consumed beforehand.
  • Lastly, in the hour prior to the session, you could use a very low-glycaemic carbohydrate energy drink. There may be no need to bolus for the carbohydrate in the drink when taken in this context as it’s absorbed slowly.

Eating 30 minutes before a training session

When you eat a meal containing carbohydrate very close to starting exercise, you can greatly reduce the carbohydrate bolus. For example, take only a quarter of your usual dose. You can consider omitting the bolus if the basal rate isn't reduced – if blood glucose is below 7mmol/L and the exercise is likely to lower your blood glucose. What you do here will be largely influenced by what your blood glucose is at the time.

General carbohydrate recommendations during exercise

  • Guidelines suggest 30–60g carbohydrate per hour of exercise or 10–15g carbs every 15–20 minutes is sufficient. It’s worth noting that even when carbohydrate may not be needed for performance, it may be needed to prevent hypoglycaemia, so the person with Type 1 diabetes can’t always follow standard sports nutrition recommendations.
  • ‘Fast-acting’ carbs are the preferred choice if the exercise is short in duration. Examples include: dextrose tablets, jelly babies, sports drinks, sports gels and fruit juice.
  • A combination of ‘fast carbs’ and ‘slow carbs’ (real foods) are preferred if the exercise is longer in duration. A banana is a good example of a slower-acting carbohydrate, to supplement the above examples of fast carbs.
  • Fluids are also important, especially when doing longer-duration exercise. Always carry a water bottle during exercise and don’t be caught in a situation where you only have a sports drink and no water as there may be times when you need fluids but not carbs.

Total IOB (from bolus insulin and basal/long-acting insulin) determines how much fuel (carbohydrate) is required before and during the session. This, is in addition to other variables such as duration and intensity of the session.

Insulin adjustments for exercise

Everyone's diabetes is different – before making any adjustments to your insulin doses you should discuss any changes with your diabetes team.

The amount and type of (basal or bolus) insulin reduction depends on the timing, duration and intensity of the exercise.

In the more elite athlete who trains regularly, the body gets accustomed to exercise, which means that any insulin adjustments tend to be smaller compared to those of the more recreational athlete.

Your basal and bolus regime

Bolus insulin adjustment

  • If you’re planning to do longer-duration, aerobic exercise soon after a meal and insulin bolus, you may want to consider reducing the insulin bolus. Compared to the resting state, exercise causes glucose to be taken up into muscle tissue very rapidly, with less need for insulin. For example, in a resting state one unit of rapid insulin may cover one apple, but during exercise that same unit may cover five apples.
  • It’s generally advised to consider reducing the meal insulin bolus if planning to exercise within 90 minutes of taking it. The bolus reduction can range from 25–75 per cent. For an hour of moderate to heavy aerobic exercise, a greater bolus reduction (50–75 per cent) is advised, compared to doing mild aerobic exercise for 30 minutes, where a 25 per cent reduction may be sufficient.

Basal insulin adjustments – applicable for insulin pumps

  • The degree by which you reduce the basal rate will depend on similar factors to those listed under the bolus adjustment section. Here are a few scenarios where a greater basal reduction may be warranted:The degree by which you reduce the basal rate will depend on similar factors to those listed under the bolus adjustment section. Here are a few scenarios where a greater basal reduction may be warranted:
    1. If performing moderate- to heavy-intensity exercise lasting 60 minutes or longer
    2. if there is IOB from a meal bolus taken before exercise
    3. If you would prefer to limit your carbohydrate intake during exercise
    4. If your blood glucose levels before exercise have been on the lower side
  • The consensus amongst researchers is that it’s preferable to make the basal reduction about 60-90 minutes before the start of planned exercise.
  • Reduce the basal insulin rate by 50-90 per cent. A good starting point is 50 per cent. Resume your normal basal rate either at the end of exercise, or in the early recovery period, according to your blood glucose response to exercise and blood glucose at the time.
  • Low blood glucose during the night may be prevented by reducing the basal rate by 20 per cent for six hours, starting at bedtime. This may not be necessary if you exercise daily, but is a useful strategy if you only exercise at the weekend or 2–3 times per week.

Please note that long-acting (background) insulin can also be reduced for exercise, although this is more complicated as it depends on the type of long-acting insulin and when it is taken. Therefore, it is best to seek advice from your diabetes team.

The power of protein

While a lot of emphasis gets put on carbohydrate, adequate protein is important for building muscle, adapting to training, recovering after training, weight loss and when recovering from an injury.

It’s worth having an idea of your protein needs and then using a calorie-tracking app for a short period to determine whether you are meeting your protein needs in order to support your goals.

It's best to meet protein needs by eating whole foods. There's a place for protein powders (such as whey powder) but these are best saved for periods when it’s difficult to eat whole foods. Children and adolescent should avoid protein powders.

General guidelines for protein needs for the average person with Type 1 diabetes engaging in exercise is 1.2–2g and should satisfy the needs of most.

Weight loss tips

Nutrition and lifestyle tips for weight loss

If losing weight is your long-term goal, it's important to do so in a safe, healthy way.

If you'd prefer to stick to a set plan, it may be worth sitting down with your diabetes team and formulating an individualised one which will work for you.

There are a few things to bear in mind when attempting to lose weight via exercise. As well as factoring in your diabetes and diet, the information below may help you to start out on the right track.

Top weight loss tips

  • Have an idea of your calorie requirements and periodically use calorie-tracking apps to see how you match up
  • Remember all calories count – a low-carbohydrate diet on its own may not result in weight loss
  • Ensure you have adequate protein at meals as it’s more filling
  • Consume the majority of your carbohydrates at meals when you are more insulin-sensitive e.g. more carbs at the meal after exercise and less at the meal before exercise
  • Prioritise sleep – aim for 7–9 hours sleep per night. Poor quality sleep may increase your calorie intake and also affect insulin sensitivity
  • Instead of only exercising at one end of the day, focus on being more active throughout the day. Try sitting less and taking standing or walking breaks throughout the day

Exercise and insulin tips for weight loss

The below strategies will ensure that minimal carbohydrates are required during exercise, which is favourable for losing weight. In order to limit the need for carbs during exercise:

  • Option 1: Perform exercise when insulin levels are lower
    • Exercise in a fasted state (e.g. before breakfast)
    • Reduce basal rate up to 90 minutes before exercise
    • Exercise 3-4 hours after a meal
  • Option 2: Exercise after meals, with significant bolus reduction
  • Option 3: Perform low-intensity exercise shortly after a meal
  • Option 4: Choose types of sport or exercise that raise, or stabilise, blood glucose

Staying safe during and after exercise

  • Always wear diabetes identification
  • Always carry fast-acting carbohydrates with you when exercising
  • Test your blood glucose before exercise, every 30 minutes during exercise, and after exercise (or use CGM)
  • Correct cautiously before and after exercise – reduce your correction bolus. Be especially careful with correcting before going to bed
  • Consider using a temporary basal reduction (if on pump therapy), but remember to make the reduction 60 minutes or more prior to exercise
  • Be aware that if you’ve had a hypo in the preceding 24 hours then you may be more at risk of going low during exercise – test frequently and be prepared to take on more carbohydrate during exercise if required
  • If hypoglycaemia is a concern, plan your exercise and meals to ensure that you exercise with low amounts of IOB
  • Do not exercise for 24 hours after severe hypoglycaemia

Examples of different types of exercise

  • Anaerobic exercise: weightlifting, tag, sprinting, diving, swimming, gymnastics, wrestling, dodgeball, volleyball, ice hockey, track cycling
  • Aerobic exercise: in-line skating, cross-country skiing, brisk walking, jogging, cycling
  • Between anaerobic and aerobic exercise: basketball, football, tennis, lacrosse, skating, skiing (slalom and downhill), field hockey, rowing (middle distance), running (middle distance)
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