Physical Activity in Postprandial Blood Glucose Control

Abstract

Physical activity is a cornerstone of blood glucose control. Regular activity is particularly important when the internal regulation of blood glucose is no longer sufficient. Physical activity can directly reduce circulating blood glucose through insulin-mediated skeletal muscle uptake. This function of physical activity appears most effective when blood glucose is high, such as in the hours after eating. Recurring postprandial blood glucose elevations are associated with increased cardiovascular disease and mortality. Physical activity to reduce elevated blood glucose, such as after eating, may therefore be considered a tool to improve blood glucose control. This thesis is divided into six chapters. A systematic review of intervention trials that consider physical activity in postprandial blood glucose control is presented in Chapter 1. The objectives of the review were to identify relevant trials, assess their quality, and identify gaps in current research. Identified trials assessed a range of physical activity intensities and durations, undertaken at various times in relation to one or more meals of varying composition. Diversity in study design and reporting prevented a quantitative summation of trial results, however studies of postprandial activity report a blood glucose improvement more frequently than studies of preprandial activity. The identified gaps of research in this field provided the rationale for the work described in Chapters 2-4. A randomised cross over trial of 41 free-living adults with type 2 diabetes is presented in Chapter 2. The objective of this trial was to compare current physical activity guidelines of 30 minutes walking each day with walking 10 minutes after each main meal. Interventions continued for two weeks, with postprandial blood glucose reduced by walking after meals. Regular walking after eating appears a practical means of interpreting physical activity guidelines for people with type 2 diabetes. A mixed-methods analysis of the motivators and impediments to regular walking is reported in Chapter 3. Twenty eight participants from the trial described in Chapter 2 went on to walk each morning, afternoon, and evening for a further three months. Self-rated health improved over this time frame as did their perception and knowledge of physical activity. Major themes that enabled a regular walking routine were the support of families, observed health benefits due to walking, and participation in a health trial. Impediments to regular walking were experienced, with a fear of walking in the dark felt strongly by female participants. Awareness of these motivators and impediments will inform the dialogue between health care professionals and their patients. Two randomised cross over trials run in parallel on 78 euglycaemic young adults are described in Chapter 4. The trials test if the timing of activity after a meal influences postprandial blood glucose. Participants cycled at very light intensity for 10 minutes either 15 or 45 minutes after a standardised meal. Activity at 45 minutes coincided with blood glucose peak, and reduced blood glucose directly after cycling was undertaken. No change in blood glucose was observed when cycling began 15 minutes after meal commencement. The work described in Chapter 5 and 6 are biochemical assessments of glycated albumin, a measure of the past two weeks blood glucose control. Work in Chapter 5 determined no relationship between glycated albumin and postprandial blood glucose measures in euglycaemic young adults. Work in Chapter 6 confirmed the stability of glycated albumin analytes in plasma under common laboratory exposures. Work of this thesis considers a physiological response to physical activity, behavioural aspects to activity adherence, and the technical assessment of a measure of blood glucose. The thesis is presented as short chapters linked by commentary from the author.