Impact of Physical Activity on Blood Glucose Stability and Energy Stores in Individuals With Type 1 Diabetes (CARBEX1)

Background

Regular physical activity enhances insulin sensitivity in both healthy subjects and patients with diabetes mellitus. However, while the effects of physical activity on glucose control are undoubtedly beneficial in patients with type 2 diabetes, exercise can cause major disturbances in blood glucose levels in type 1 diabetic individuals. Hypoglycemia is a common complication in patients with T1DM engaging in endurance activities such as running and cycling. So far there are limited strategies suggested to improve exercise-related blood sugar self-management. Current recommendations focus on variation in timing and dosage of insulin administration and adjustments in carbohydrate intake. Since rapid adaptation of insulin dosage may be difficult, alternative strategies to improve exercise-related glucose stability are required. Increasing evidence suggests that intermittent high intensity exercise (IHE), by triggering a counterregulatory hormone response, may counter-balance the risk of exercise-associated hypoglycemia. However, previous studies investigating IHE in T1DM were limited by heterogeneous study populations, comparably short exercise protocols, and deficits in standardization procedures. In addition, a comprehensive assessment of the underlying fuel metabolism has not been performed so far. As a consequence, the results remain controversial and their interpretation as well as applicability are restricted.

A further alternative strategy to maintain stable glycemia during exercise may be deduced from recent studies in non-diabetic individuals suggesting that the combined ingestion of fructose and glucose during exercise provides the liver with an increased amount of gluconeogenic precursors, thereby reducing consumption of endogenous glycogen stores.Moreover, conversion of fructose into glucose and lactate may provide constant and efficient fuel for working muscles. However, studies assessing the impact of fructose ingestion during exercise in patients with T1DM have not been performed so far.

Objective

The investigators aim to assess the impact of two novel non-pharmaceutical and easily feasible approaches on exercise-related blood glucose stability and its underlying exercise-related fuel metabolism in patients with T1DM.

Substudy A will assess the influence on exercise-related glycemia and fuel metabolism of an IHE protocol compared to an iso-energetic continuous exercise (CONT). It will be investigated whether individuals reach more stable blood glucose levels when engaging in IHE compared to CONT.

Substudy B will investigate whether fueling the patients with a mixed oral 1:1 glucose-fructose carbohydrate solution will maintain glucose values within a more stable range when compared to carbohydrate supplementation by glucose alone.

Methods

Blood glucose levels, counterregulatory hormones, metabolites such as lactate and free fatty acids as well as inflammatory biomarkers will be assessed by regular blood samplings. By means of oral and intravenously given stable isotopes (U-13 C glucose and 2H glucose) exercise-related glucose kinetics will be investigated. Exercise-induced glycogen consumption will be measured using magnetic resonance spectroscopy technology. Late glycemic excursions will be recorded by continuous glucose monitoring systems.

In order to validate 13C magnetic resonance spectroscopy (MRS) measurement of hepatic and myocellular glycogen content a pre-study involving 10 patients and an equal number of matched healthy controls will be performed (validation and reproducibility study).