Management of Type 1 Diabetes in an Elite Endurance Athlete

BACKGROUND

Type 1 diabetes mellitus (T1DM) is a chronic metabolic disorder that affects the body’s ability to produce insulin, leading to hyperglycemia (1). Managing blood glucose levels is crucial for individuals with T1DM to prevent hypoglycemia, hyperglycemia, and other related complications. There are multiple benefits of exercise in patients with T1DM, including increased insulin sensitivity, improved glucose uptake by muscles, and counteracting after-meal hyperglycemia. Exercise in these patients also helps control weight, lowers blood pressure, improves cholesterol levels, and strengthens muscles and bones. To optimize blood glucose control during exercise, athletes with T1DM must be aware of factors that complicate glycemic management, such as varying types of physical activity, differences in insulin regimens, food intake for exercise, and the importance of maintaining steady, in-range blood glucose levels before, during, and after exercise activities.

Gravel bicycling is a sport increasing in popularity that requires a high level of physical fitness and endurance. Any type of endurance exercise in those with diabetes poses unique challenges that require careful management of blood glucose levels to prevent exercise-induced hypoglycemia, hyperglycemia, or other complications. Yardley (2) states fear of hypoglycemia as a major barrier for athletes with T1DM. The American Diabetes Association (ADA) Workgroup on Hypoglycemia defined hypoglycemia in people with diabetes as “all episodes of abnormally low plasma glucose concentration that expose the individual to potential harm” (3). Although fear of hypoglycemia or other complications remains present, evidence is emerging to support endurance athletes with T1DM.

Maintaining consistent and optimal blood-glucose levels can be difficult for athletes with T1DM; however, there are strategies available to manage blood-glucose levels and achieve exercise and athletic goals (4). These strategies include administering exogenous insulin through external computerized medical devices or via injection, nutritional macronutrient intake, and continuous blood-glucose monitoring devices. During training and rest periods, some athletes with diabetes choose to ingest lower levels of carbohydrates; however, during longer distances and higher endurance events, athletes will consume higher levels of carbohydrates to avoid hypoglycemic events and support athletic performance (5).

Every day, more individuals with T1DM train to compete at the elite level in all sports, including competitive cycling, Olympic games, football, basketball, soccer, and other sports. Although research is emerging to support these athletes and management of T1DM, little remains known about dietary patterns, nutritional strategies, and glycemic response to endurance exercise in these athletes competing in elite endurance events. This case study examines a bicycle endurance athlete who completed a 100-mile (161-km) gravel race and the effects of nutrition and exercise and the impact these factors had on power, cadence, speed, heart rate, and blood sugar throughout the race. This case report was approved by the Arkansas Colleges of Health Education Institutional Review Board, and the athlete provided written consent to participate in this study.

CASE REPORT

The athlete was a 33-year-old man, diagnosed with T1DM at age 23. This athlete had successfully completed a 100-mile (161-km) gravel bike ride previously, and successfully completed a weekly training regime leading up to the race. At the time of the race, the athlete had a body weight of 188.4 lb (85.6 kg), height of 70 inches (178 cm), and body mass index of 27.9 kg·m⁻².

The gravel race is a gravel route through remote and rugged highlands spanning 2 states. The challenging course features rarely maintained roads with loose, rocky gravel, a few pavement sections, and water crossings and bridges. On the day of the race, the weather ranged from 59°F to 89.6°F (15°C–32°C) with an average temperature of 71.8°F (22°C). Racers were allowed to consume food and drinks freely, and the athlete tracked his consumption throughout the race; his food log is shown in Table 1. All food and drink were provided by the participant with the exception of an Uncrustables Peanut Butter and Jelly sandwich provided by the race officials to all participants at mile marker 77 (124 km). The participant consumed three and one-half 850-mL bottles of Science & Sport Beta Fuel throughout the entire race. Using the athlete’s food journal, carbohydrate and other macronutrients were analyzed in addition to other recorded data. The athlete completed the race on a Viathon G1 gravel bike with 42-mm Boken DoubleCross tires. Power was measured with a Stages single-sided power meter, and distance, heart rate, temperature, power, and cadence were tracked using a Garmin Edge 520 head unit. Blood glucose was measured via the participant’s personal Dexcom G6 with insulin delivered via tandem pump.

TABLE 1.Race day food and hydration log.

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During the week of the event, the athlete’s glucometer reported 71% of time in target range (70–180 mg·dL⁻¹) and 1% of time below goal range (<70 mg·dL⁻¹). During the 3 days prior to the event, the athlete had notable postprandial glucose excursions but no reported hypoglycemic episodes. Three days prior to the event, the athlete had an overnight glucose excursion lasting from 7 pm to 4 am (9 hours) with a peak glucose level of approximately 375 mg·dL⁻¹. The next evening showed a similar event but with a shorter duration of 5 hours. The day prior to the event showed a postprandial excursion beginning around 2 pm and ending around 7 pm (5 hours) with a peak glucose of approximately 375 mg·dL⁻¹. For this period, dietary records, insulin pattern management data, and training logs were unavailable.

During the race, the athlete ingested 22 g of carbohydrates at 7:30 am (zone 1), 9:00 am (zone 2), 10:30 am (zone 3), and 12:30 pm (zone 4); 50 g of carbohydrates at 1:30 pm (zone 5); and 22 g of carbohydrates at 3:00 pm (zone 6) before the end of the race at 5:00 pm. In zone 1 the athlete’s blood sugar declined at a rate of 1.77 mg·dL⁻¹ per minute with an average heart rate of 154 b·min⁻¹ and average power output (aPWR) of 180 W. In zone 2 his blood glucose declined at a rate of 0.35 mg·dL⁻¹, with an average heart rate of 152 b·min⁻¹ and aPWR 174 W. In zone 3 it decreased at 0.43 mg·dL⁻¹ per minute, with 146 b·min⁻¹ average heart rate and aPWR 157 W. In zone 4 it decreased at 0.86 mg·dL⁻¹ per minute, with an average heart rate of 128 b·min⁻¹ and aPWR 95 W. During zone 5 he consumed 50 g of carbohydrates and his blood sugar peaked early at 183 mg·dL⁻¹ and then peaked again at 201 mg·dL⁻¹ at 2:59 pm. During this time his blood glucose increased at an average rate of 0.20 mg·dL⁻¹ with an average heart rate of 120 b·min⁻¹ and aPWR of 82 W. In zone 6 his blood glucose decreased at a rate of 0.68 mg·dL⁻¹ with a 126 b·min⁻¹ average heart rate and aPWR of 101 W (Figure 1).

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DISCUSSION

When calculating total energy intake, a macronutrient distribution of 60% carbohydrate, 15% protein, and 25% fat is the typical recommendation to support endurance training (6). This athlete was able to maintain glucose levels above 70 mg·dL⁻¹ throughout the race but did have 2 occurrences of being at or near this threshold value. This suggests that the approximately 50 g of carbohydrates per hour was sufficient for this athlete to prevent exercise induced hypoglycemia. However, the American College of Sports Medicine recommends as much as 90 g per hour of carbohydrates for maximum performance (7). As expected, the athlete exhibited signs of fatigue as the race progressed, particularly toward the end of the race. Following consumption of carbohydrates, the athlete did experience a hyperglycemic event, which likely contributed to or intensified the fatigue observed.

Endurance athletes are at an increased risk of dehydration (8), combined with hyperglycemia. This could lead to decreased performance, as indicated by this athlete’s reduced power output throughout the duration of the race. This athlete also demonstrated an increase in blood glucose levels, likely due to the continued consumption of carbohydrates and decreased sensitivity to insulin because of the decreased power output. The findings of this case report highlight the complex relationship between carbohydrate intake, blood glucose dynamics, and physiological parameters during endurance racing. This also suggests there is a need for more specific guidelines for athletes with T1DM who participate in endurance events. Specifically, further research is needed on endurance exercise nutrition for optimal performance as well as hydration guidelines.

The study protocol was approved by the Institutional Review Board of Arkansas Colleges of Health Education in Fort Smith, Arkansas. The authors certify that they have no affiliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article.