The competitive athlete with type 1 diabetes

Abstract

Regular exercise is important for health, fitness and longevity in people living with type 1 diabetes, and many individuals seek to train and compete while living with the condition. Muscle, liver and glycogen metabolism can be normal in athletes with diabetes with good overall glucose management, and exercise performance can be facilitated by modifications to insulin dose and nutrition. However, maintaining normal glucose levels during training, travel and competition can be a major challenge for athletes living with type 1 diabetes. Some athletes have low-to-moderate levels of carbohydrate intake during training and rest days but tend to benefit, from both a glucose and performance perspective, from high rates of carbohydrate feeding during long-distance events. This review highlights the unique metabolic responses to various types of exercise in athletes living with type 1 diabetes. Graphical abstract.

Keywords: Athlete; Carbohydrate; Competition; Continuous glucose monitoring; Exercise; Glucose; Insulin; Nutrition; Review; Sport; Type 1 diabetes.

Graphical abstract

Fig. 1

Example training day (a) and competition day (b) for a competitive athlete with type 1 diabetes. A number of variables need to be considered and controlled by an athlete with type 1 diabetes, including glucose monitoring, basal and bolus insulin-dose modifications, snacks and meals, hypo- and hyperglycaemia mitigation, hydration and stress management. Although some flexibility may be allowed on training days with regard to the timing of training and meals, this flexibility is lost on competition days due to strict competition schedules. Note that this is an example and will differ depending on numerous factors such as the event that the athlete competes in. This figure is available as part of a downloadable slideset

Fig. 2

Energy substrates for exercise. The source of energy substrates during exercise varies depending on exercise duration. During skeletal muscle contraction, in the first few seconds of exercise, energy is provided from ATP, which is immediately resynthesised from phosphocreatine (PC). For exercise of longer duration, ATP resynthesis occurs by catabolising other fuel sources (lipids and carbohydrates). Figure based on previously published data [102, 103]. This figure is available as part of a downloadable slideset

Fig. 3

Circulating insulin levels in physically active individuals with type 1 diabetes. The values shown represent the insulin concentration as measured before (rest) and soon after the end of exercise in a variety of previously published studies, which included various cohorts/conditions: non-diabetic control participants (Non-DM); participants with type 1 diabetes who underwent high- (HGI-CHO) or low- (LGI-CHO) carbohydrate feeding interventions; participants with type 1 diabetes who underwent bolus insulin-dose reductions (full bolus; 75% bolus; 50% bolus; 25% bolus); participants with type 1 diabetes who underwent basal insulin-dose reductions, along with bolus dose reductions for MDI (full basal/50% bolus; 80% basal/50% bolus); participants with type 1 diabetes who had low (15 mU m⁻² min⁻¹) or high (50 mU m⁻² min⁻¹) intravenous insulin infusions; and type 1 diabetic participants who underwent basal insulin rate reductions for CSII (pump suspend; 50% basal rate; 20% basal rate). The mode of exercise and duration of activity is shown on the x-axis. Data are from select studies [, , , –108] and were analysed by R. M. Bracken. This figure is available as part of a downloadable slideset

Fig. 4

Carbohydrate intake patterns in athletic individuals with type 1 diabetes. (a) Daily macronutrient intake from carbohydrates in 252 active adults with type 1 diabetes and of varying athletic level who were surveyed about their carbohydrate intake patterns. Approximately 40% self-reported carbohydrate consumption within the current acceptable macronutrient distribution range of 45–65% of energy intake (>200 g/day) [109], whereas ~30% consciously moderated their carbohydrate intake (100–200 g/day), typically by avoiding starchy or sugary foods. The remainder described following either a low-carbohydrate diet (17% of participants; ~40–99 g/day) or a very-low-carbohydrate diet (13% of participants), with a meal plan of carbohydrate intake of <40 g/day (S. R. Colberg, unpublished data). (b) Carbohydrate intake rates during endurance training and competition events: Data are from select studies and were analysed by R. M. Bracken [, , –76]. The x-axis provides information on exercise duration (h:min) and also profiles the exercise distance and mode used in each of the published studies. Mean carbohydrate intake rate across the studies analysed was 0.70 ± 0.26 g [kg body mass]⁻¹ h⁻¹ (50 ± 18 g/h). BM, body mass. This figure is available as part of a downloadable slideset

Fig. 5

Proposed CGM-based targets for athletes with type 1 diabetes during training (a) and competition (b). Targets for training days are based on the international consensus [83], while the targets for competition are based on the opinion of the authors. Individual targets should be set by the individual’s healthcare provider with consideration of several variables, including age, duration of diabetes, diabetes-related complications and level of hypoglycaemia awareness. In both training and competition in individuals aged <25 years, if the HbA_1c goal is <58 mmol/mol [7.5%], then the TIR target should be set to ~60% but a goal of <4% time below target range (<3.9 mmol/l glucose) should be maintained. ^aIncludes percentage of values >13.9 mmol/l. ^bIncludes percentage of values <3.0 mmol/l. This figure is available as part of a downloadable slideset

Fig. 6

Additional travel considerations for athletes with type 1 diabetes. A summary of practical considerations that an athlete with type 1 diabetes should take into account when travelling for athletic competition. Long-distance travel typically increases sedentary time (not shown), can alter food choices and tends to be associated with risk of hypo- and hyperglycaemia [99]. Increased vigilance around glucose monitoring and insulin-dose alterations, as well as access to healthy dietary options, diabetes supplies and, at least, light physical activity (not shown), should be considered. This figure is available as part of a downloadable slideset