Daily energy expenditure, cardiorespiratory fitness and glycaemic control in people with type 1 diabetes

Abstract

Objective: Encouraging daily physical activity improves cardiorespiratory fitness and many cardiovascular risk factors. However, increasing physical activity often creates a challenge for people with type 1 diabetes, because of difficulties maintaining euglycemia in the face of altered food intake and adjustments to insulin doses. Our aim was to examine the triangular relationship between glucose control measured by continuous glucose monitoring system (CGMS), objective measures of total daily energy expenditure (TEE) recorded by a multi-sensory monitoring device, and cardiorespiratory fitness (CRF), in free-living subjects with type 1 diabetes.

Research design and methods: Twenty-three individuals (12 women) with type 1 diabetes who were free from micro- and macrovascular complications were recruited. TEE and glucose control were monitored simultaneously for up to 12 days, using a multi-sensory device and CGMS respectively. CRF was recorded as V02 max from a maximal treadmill test with the Bruce protocol.

Results: Subjects (mean±SD) were aged 37±11 years, with BMI = 26.5±5.1 kg.m⁻², HbA1c = 7.7±1.3% (61±14 mmol/mol) and V02 max (ml.min⁻¹.kg⁻¹) = 39.9±8.4 (range 22.4-58.6). TEE (36.3±5.5 kcal.kg⁻¹.day⁻¹) was strongly associated with CRF(39.9±8.4 ml.min⁻¹.kg⁻¹) independently of sex (r = 0.63, p<0.01). However, neither TEE (r = -0.20, p = 0.36) nor CRF (r = -0.20, p = 0.39; adjusted for sex), were significantly associated with mean glycaemia measured by CGMS.

Conclusion: Higher levels of energy expenditure (due to a more active lifestyle) are associated with increased cardiorespiratory fitness, but not necessarily better glycaemic control. Since increased levels of energy expenditure and good glycaemic control are both needed to protect against diabetes-related complications our data suggest they need to be achieved independently.

Figure 1. CONSORT flow diagram showing enrollment and retention of volunteers in the study of energy expenditure in type 1 diabetes.

Figure 2. 3-D Scatter plot for cardiorespiratory fitness (CRF), mean daily total energy expenditure (TEE) and mean blood glucose (MBG) of study participants.

Blue diamonds show the relationship between CRF and TEE with the solid red line showing the linear fit (CRF  =  TEE + 2.3, R²  =  0.47). Blue circle markers show the corresponding MBG for each individual.

Figure 3. Summary of key findings describing the triangular relationship between glycaemic control, daily energy expenditure and cardiorespiratory fitness.

Figure 4. Plots for daily mean blood glucose (MBG) against daily total energy expenditure (TEE) for two individuals (every blue cross represents a new day).

These two participants were chosen to illustrate the two extremes (amongst participants) in the relationships between daily MGB and TEE. Participant A showed very little day to day variability (CV TEE  =  0.04, MBG  =  0.07), whereas in contrast, Participant B showed much greater variability (CV TEE  =  0.12, MBG  =  0.15).