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Adjusting insulin and carbohydrates for physical exercise in type 1 diabetes

Stephen Bain, Jeffrey W Stephens, Richard Bracken
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If physical exercise is promoted as part of the management of those with type 1 diabetes (American College of Sports Medicine and American Diabetes Association, 1997), why are so many failing to reach Department of Health minimum physical activity standards? Fears about loss of glycaemic control predominate for those with type 1 diabetes, perhaps compounded by the lack of physical activity education as part of under- or post-graduate healthcare professional training. “In-house” structured education programmes (e.g. DAFNE [Dose Adjustment For Normal Eating], DAFYDD [Dose Adjustment For Your Daily Diet] and BERTIE [Bournemouth Type 1 Intensive Education Programme]) offer hope, but NHS budget cuts threaten service provision, and a lack of emphasis on physical activity in time-constrained consultations means that the healthcare provider is often unable to promote physical activity advice. Here we offer practical, evidence-based tips for addressing the topic of adjusting insulin and carbohydrates for physical exercise in type 1 diabetes.

Research studies have explored adjustments to diet and medication that improve the acute glycaemic responses to physical activity in people with type 1 diabetes. These changes may form the basis of an individualised “acute exercise management strategy” that instils more confidence for people with type 1 diabetes and their healthcare professionals to engage in physical activity and obtain the many metabolic and psychological health benefits of being regularly active.

On the assumption that individuals have been assessed by their GP or hospital specialist and present minimal complications that preclude them from starting a physical activity programme in line with Department of Health (2011) guidelines (see Box 1), a person with type 1 diabetes may need to make individualised adjustments to insulin and carbohydrate intake before, during and after a bout of exercise (Figure 1 provides an example).

Insulin and carbohydrate adjustments for aerobic exercise
Safe blood glucose ranges for exercise
According to the International Diabetes Federation (2014), pre-exercise blood glucose should ideally be >6 mmol/L. If the level is >14 mmol/L, ketones should be tested and exercise delayed until the values decline. A note of caution here is that, since account is not made of the direction of change in blood glucose in the hours prior to measurement, a 60-minute pre-exercise blood glucose sample may provide additional confidence.

Basal–bolus insulin reduction
In people with relatively well-controlled type 1 diabetes, insulin detemir is associated with less hypoglycaemia during and after exercise than insulin glargine (but not NPH insulin; Arutchelvam et al, 2009). However, in the majority of cases, basal insulin corrections are not normally made.

Research examining adjustments to pre-exercise rapid-acting (bolus) insulin has explored reductions ranging from 10% to 90% (Rabasa-Lhoret et al, 2001; Mauvais-Jarvis et al, 2003; Grimm, 2005; De Feo et al, 2006; West et al, 2010; 2011b). Based on these experiments, a prudent start point appears to be an approximate 50% reduction in rapid-acting insulin made 30–60 minutes before activity (West et al, 2011b).

Carbohydrate ingestion
For aerobic activity, bolus insulin reductions are usually made alongside consumption of carbohydrate. Carbohydrates come in different forms. Some that enter the blood stream rapidly (i.e. high-glycaemic-index [high-GI] carbohydrates such as glucose and maltodextrin) are important in alleviating hypoglycaemia, but slower alternatives (i.e. low-GI carbohydrates such as fructose and isomaltulose) have been shown to provide equal energy, reduce glycaemic fluctuations and produce equivalent exercise performance (West et al, 2011a; Bracken et al, 2012). Current recommendations suggest ingesting an upper limit of 1 g carbohydrate per kg of body mass per planned hour of exercise, in a 6–10% solution. As an example, an 80 kg male aiming to perform 30 minutes of aerobic cycling might consume a 10% solution of a low-GI carbohydrate (0.40 L) that delivers 40 g of available carbohydrate. After initial blood glucose monitoring, further refinement on amounts may be applied.

The pre- and post-exercise periods
A combined insulin reduction and carbohydrate feeding strategy 30–60 minutes before running can preserve blood glucose concentration after exercise in people with type 1 diabetes who are undertaking physical activity (West et al, 2011b).

Importantly, there is a need to adjust insulin and carbohydrate following physical activity because performing exercise sensitises tissues to insulin and independently increases muscle and liver glucose uptake. Accordingly, in addition to pre-exercise adjustments, consumption of a low-GI meal and a 50% post-exercise rapid-acting insulin dose (1 hour after exercise) reduces glycaemic fluctuations and protects against hypoglycaemia for up to 8 hours (Campbell et al, 2013; 2014).

Insulin and carbohydrate adjustments for strength exercise
There is much less information available on the adjustments necessary for people with type 1 diabetes who are performing strength exercise. In contrast to aerobic exercise, strength exercises can cause large acid–base shifts and counter-regulatory responses that increase blood glucose concentrations following the period of physical activity. The amount of weight-lifting in a session can determine the degree of hyperglycaemia (Turner et al, 2014a). Thus, it seems (for morning exercise at least) that there is a minimal need to consume carbohydrates for strength exercise lasting approximately 30 minutes. However, if exercise-induced hyperglycaemia regularly occurs it may be useful to deliver a small rapid-acting insulin dose (Turner et al, 2014b).

Regular exercise is promoted as a cornerstone of good glycaemic management in type 1 diabetes, yet much work remains to be done to promote physical activity so that it is on an equal footing with diet and medication. We need to instil more confidence in people with the condition and primary care staff to manage blood glucose before, during and after exercise, in order to allow the many health benefits of being active to be achieved. Everyone’s response to exercise will be different, but it is hoped that knowledge of the typical glycaemic response to aerobic or anaerobic exercises may help in the development of an individualised “acute exercise management strategy”.

Questions to test your knowledge
The answers are not always to be found in this article.

  1. Fructose is a high-glycaemic-index carbohydrate.
    Is this true or false?
  2. It is usual to adjust rapid-acting insulin before exercise.
    Is this true or false?
  3. Insulin requirements remain unaltered following aerobic activity.
    Is this true or false?
  4. Thirty minutes of strength exercise is likely to cause an increase in blood glucose concentrations.
    Is this true or false? 

Answers: 1 – false; 2– true; 3 – false; 4 – true.


American College of Sports Medicine, American Diabetes Association (1997) American College of Sports Medicine and American Diabetes Association joint position statement. Diabetes mellitus and exercise. Med Sci Sports Exerc 29: i–vi
Arutchelvam V, Heise T, Dellweg S et al (2009) Plasma glucose and hypoglycaemia following exercise in people with Type 1 diabetes: a comparison of three basal insulins. Diabet Med 26: 1027–32
Bracken RM, Page R, Gray B et al (2012) Isomaltulose improves glycemia and maintains run performance in type 1 diabetes. Med Sci Sports Exerc 44: 800–8
Campbell MD, Walker M, Trenell MI et al (2013) Large pre- and postexercise rapid-acting insulin reductions preserve glycemia and prevent early- but not late-onset hypoglycemia in patients with type 1 diabetes. Diabetes Care 36: 2217–24
Campbell MD, Walker M, Trenell MI et al (2014) A low glycaemic index meal and bedtime snack prevent postprandial hyperglycaemia and protect patients from early, but not late-onset hypoglycaemia following evening exercise in patients with type 1 diabetes. Diabetes Care [in press]
De Feo P, Di Loreto C, Ranchelli A et al (2006) Exercise and diabetes. Acta Biomed 77(Suppl 1): 14–7
Department of Health (2011) UK physical activity guidelines. DH, London. Available at: (accessed 28.05.14)
Grimm JJ (2005) Exercise in type 1 diabetes. In: Nagi D (ed). Exercise and sport in diabetes. Wiley, Hoboken, NJ, USA: 25–43
International Diabetes Federation (2014) Physical activity. IDF, Brussels, Belgium. Available at: (accessed 28.05.14)
Mauvais-Jarvis F, Sobngwi E, Porcher R et al (2003) Glucose response to intense aerobic exercise in type 1 diabetes. Diabetes Care 26: 1316–7
Rabasa-Lhoret R, Bourque J, Ducros F, Chiasson J (2001) Guidelines for premeal insulin dose reduction for postprandial exercise of different intensities and durations in type 1 diabetic subjects treated intensively with a basal-bolus insulin regimen (Ultralente-Lispro). Diabetes Care 24: 625–30
Turner D, Gray BJ, West DJ et al (2014a) Efficacy of an individually determined rapid-acting insulin dose algorithm for improving post-resistance exercise glycemia in type 1 diabetes patients. Presented at: 74th Scientific Sessions of the American Diabetes Association (0726-P). San Francisco, CA, USA, 13–17 June
Turner D, Luzio S, Gray BJ et al (2014b) Impact of single and multiple sets of resistance exercise in type 1 diabetes. Scand J Med Sci Sports 20 Mar [epub ahead of print]
West D, Morton R, Bain SC et al (2010) Blood glucose responses to reductions in pre-exercise rapid-acting insulin for 24 h after running in individuals with type 1 diabetes. J Sports Sci 28: 781–8
West D, Morton R, Stephens JW et al (2011a) Isomaltulose improves post-exercise glycemia by reducing CHO oxidation in T1DM. Med Sci Sports Exerc 43: 204–10
West D, Stephens JW, Bain SC et al (2011b) A combined insulin reduction and carbohydrate feeding strategy 30 min before running best preserves blood glucose concentration after exercise through improved fuel oxidation in type 1 diabetes mellitus. J Sports Sci 29: 279–89

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