Saudi Cultural Missions Theses & Dissertations
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Item Restricted Assessing appetite responses to physical activity using functional magnetic resonance imaging(Loughborough University, 2024-03-13) Dera, Abdulrahman; Stensel, David; King, James; Thackray, AliceThe relationship between physical activity, sedentary time, and appetite control has potential implications for weight management. Limited evidence suggests that regular physical activity may influence responsiveness to visual food cues in reward-related brain regions. In the past few years, studies have increasingly focused on neural regulation of appetite and feeding. Despite this, there is scarce research examining how physical activity is associated with brain responses to food cues and the circulating peptides that are implicated in the regulation of appetite within the brain. The first study in this thesis (Chapter 4) is a systematic review of functional magnetic resonance imaging (fMRI) studies examining the effect of physical activity on neural responses to visual food cues in humans. Exercise, both acute and chronic, appears to lower food-cue reactivity in several brain regions, including the insula, hippocampus, orbitofrontal cortex (OFC), postcentral gyrus, and putamen, especially when participants view images of high-energy-density foods. Research suggests that acute exercise may enhance the appeal of low-energy-density food choices. Several cross-sectional studies have demonstrated that individuals with high levels of self-reported physical activity show less reactivity to food cues, particularly cues depicting high-energy-density foods, in the insula, OFC, postcentral gyrus, and precuneus. The results of this review suggest that physical activity may affect food-cue reactivity in motivational, emotional, and reward-related brain regions, possibly indicating a hedonic appetite suppression effect. However, considering methodological variability across a limited number of studies, conclusions should be drawn with caution. The second study reported in this thesis (Chapter 5) used a randomised crossover design to investigate the acute effect of vigorous-intensity exercise (treadmill running) on cerebral blood flow (CBF). This study explored the time course of CBF changes after acute exercise in healthy men using fMRI and its implications for food-cue reactivity paradigms. Overall, differences between trials were evident in grey matter and regional CBF, but the CBF time course was not influenced by exercise, suggesting that food-related blood-oxygen-level-dependent (BOLD) acquisitions after exercise may not be time-sensitive. In future studies, it may be necessary to acquire BOLD and CBF data simultaneously so that differences in CBF between trials that may affect the interpretation of brain food cue reactivity can be considered. ii The third study reported in this thesis (Chapter 6) is a cross-sectional study examining the association of physical activity and sedentary behaviour with neural responses to visual food cues in adults. A negative relationship was found between moderate to vigorous physical activity (MVPA) and food-cue reactivity in the hippocampus, insula, amygdala, middle frontal gyrus, and precentral gyrus. A positive association was identified between MVPA and food-cue reactivity in the striatum, whereas sedentary time was positively associated with food reactivity in the posterior cingulate gyrus and paracingulate gyrus, independently of BMI. Moreover, fasting glucagon-like peptide-1 (GLP-1) concentrations correlated negatively with brain reactivity in areas associated with cognition, emotion, and reward. This suggests that low GLP-1 concentrations may increase hunger and motivation to seek food. Fasting glucose concentrations were negatively associated with brain reactivity in response to food cues in the postcentral gyrus, potentially indicating heightened sensitivity to food cues when glucose concentrations are low. Fasting peptide tyrosine-tyrosine (PYY), a hormone associated with feeling full, was negatively associated with food cue reactivity in the middle frontal gyrus. No relationship was observed between fasting acylated ghrelin concentrations, overall appetite perceptions, and brain responses to food cues. This thesis highlights that physical activity and sedentary behaviour influence brain responses to visual food cues. The three studies emphasise the importance of continued research examining links between physical activity and appetite control. The findings provide a broad understanding of how physical activity and exercise (acute and chronic) affect food-cue and appetite perception, including both the neural and hormonal components involved in appetite perception. Understanding of appetite regulation in the brain has been further enhanced by considering CBF, neural pathways, and appetite related hormones. Using this foundation, further research can be conducted exploring ways to improve lifestyles and eating habits.25 0Item Restricted Effects of Physical Activity, Exercise and Breakfast Timing Manipulations on Glucose Metabolism in Healthy Adolescents(Saudi Digital Library, 2025-10-27) Afeef, Sahar; Tolfrey, Keith; Barrett, Laura A; Zakrzewski-Fruer, Julia KPostprandial hyperglycaemia is associated with an increased risk of type 2 diabetes (T2D) and cardiovascular disease (CVD). Even in healthy individuals, hyperglycaemia can adversely impact cardiometabolic health. Multiple rises and falls in glucose concentrations (i.e., glycaemic variability) may harm vascular health. Since most of the day is often spent in a postprandial state, measuring glucose concentrations over this critical period is vital to assess glycaemic profile. The novelty of continuous glucose monitoring (CGM) systems enables the assessment of glycaemic variability and postprandial glycaemia with reduced invasiveness and under free-living conditions. Since cardiometabolic risk factors were found to begin early in life, interventions focusing on moderating postprandial glycaemia and glycaemic variability through physical activity (PA) and diet manipulations should start early in life. Therefore, this thesis aimed to investigate postprandial glycaemic responses and glycaemic variability in relation to PA, exercise and breakfast timing manipulations in healthy adolescents aged 11 to 14 years. The first experimental study, Chapter 4, compared interstitial fluid glucose concentration ([ISFG]) obtained by CGM (i.e., FreeStyle Libre) against capillary plasma glucose concentration ([CPG], reference method) in response to an oral glucose tolerance test (OGTT, 5 time points including fasting) and treadmill exercise at different intensities (5 time points) in 17 healthy adolescents (9 girls, mean ± SD age 12.8 ± 0.9 y, BMI 18.4 ± 2.1 kg∙m−2). The overall mean absolute relative difference was 13.1 ± 8.5%. The [ISFG] was significantly lower than [CPG] 15 (−1.16 mmol·L−1, −9.7%) and 30 min (−0.74 mmol·L−1, −4.6%) after OGTT. Yet, post-OGTT glycaemic responses assessed by total (tAUC) and incremental (iAUC) area under the curves were not significantly different with trivial to small effect sizes (P ≥ 0.084, d = 0.14 – 0.45). These results indicate that CGM is an acceptable device reflecting postprandial glycaemic responses (i.e., AUC) that have high relevance to CVD risk. Non-significant site by timepoint interactions were observed during the treadmill exercise tests (P ≥ 0.614), indicating that the pattern of [ISFG] assessed by CGM was similar to [CPG] across the time points. Consequently, CGM were used in the two subsequent studies (Chapters 5 & 6). Using objective monitoring devices (i.e., Actigraph and CGM), Chapter 5 examined the associations of daily glycaemic variability with sedentary time and PA levels measured under free-living conditions in 37 healthy adolescents (24 girls, 12.7 ± 1.0 y, 20.1 ± 3.7 kg∙m−2). Glycaemic variability measures were not significantly associated with time spent sedentary and PA levels after accounting for age, sex, maturity status, accelerometer wear time and % body fat (P ≥ 0.071). However, there are some potential associations between glycaemic variability measures and sedentary time and MVPA. The findings suggest that accumulating 60 min MVPA daily tended to associate with 0.04 mmol∙L−1 reduction in StDevG (β = –0.00068, P = 0.087) and 0.7% reduction in glucose CV (β = –0.012038, P = 0.086). The magnitude of changes is small, and the metabolic health implications of such reductions are not known. Furthermore, the results suggest that accumulating 60 min of sedentary time seems to be associated with 0.3% higher glucose CV (β = 0.005692, P = 0.071), yet the same duration spent in MVPA tends to be associated with 0.7% lower glucose CV (β = –0.012038, P = 0.086), suggesting a greater impact of MVPA on glycaemic variability. Thus, encouraging reduced sedentary time combined with participation in MVPA may reduce glycaemic variability in healthy adolescents with small variations in blood glucose concentrations. Using CGM, Chapter 6 investigated the acute effect of school-based exercise bouts on postprandial glycaemia and 24 h glycaemic variability in 14 healthy adolescents (6 girls, 12.8 ± 1.0 y, 18.0 ± 1.6 kg∙m−2). The participants performed three experimental conditions in a fixed pre-determined order on three consecutive days: day 1) moderate intensity exercise condition (MIE, 30-min continuous brisk walking); day 2) no-exercise control condition (CON); day 3) high intensity intermittent exercise condition (HIIE, 30-min of 10 × 30-s sprints interspersed with 2.5-min brisk walking bouts). They performed the exercise conditions or no-exercise then consumed three standardised meals (breakfast and lunch at school and dinner at home) at fixed times. Thirty-minute bouts of MIE and HIIE did not change postprandial glycaemia (P ≥ 0.203) or 24-h glycaemic variability (P ≥ 0.281) significantly in this small sample of healthy adolescents. Although non-significant, the reduction in post-breakfast glucose iAUC was moderate for MIE (−0.24 mmol·L−1; P = 0.589; d = 0.77) and large for HIIE (−0.26 mmol·L−1; P = 0.444; d = 0.86) compared with CON. Non-significant, moderate (0.37 mmol·L−1; P = 0.219; d = 0.70) and large (0.42 mmol·L−1; P = 0.203; d = 0.81) increases in post-lunch glucose iAUC were observed for MIE and HIIE compared with CON. Furthermore, the effect size in post-dinner glucose iAUC were trivial to small between conditions, suggesting a short residual effect of exercise lasting for two meals. The mismatch between the probability values and effect sizes was a consequence of the COVID-reduced sample. The ramifications of these exercise effects are unclear and need to be confirmed in a larger sample of adolescents. The last experimental study, Chapter 7, examined the effect of early morning (EM-BC, 08:30) and mid-morning (MM-BC, 10:30) breakfast consumption compared with breakfast omission (BO) on the glycaemic and insulinaemic responses to the second meal (i.e., lunch) in 15 healthy adolescent girls (13.1 ± 0.8 y, 19.8 ± 3.1 kg∙m−2) who skipped breakfast habitually. The main finding from this study was that MM-BC significantly reduced post-lunch glucose tAUC (–10%; P = 0.002, d = 0.68) and iAUC (–36%; P < 0.001, d = 1.44) compared with BO, with moderate to large effects. However, the EM-BC resulted in non-significant reductions in post-lunch glucose tAUC (–5%; P = 0.195, d = 0.36) and iAUC (–15%; P = 0.077, d = 0.52) compared with BO, with small to moderate effects. Furthermore, MM-BC resulted in moderate reductions in post-lunch peak glucose compared with both BO (–1.03 mmol·L−1; P = 0.001, d = 0.74) and EM-BC (–1.03 mmol·L−1; P = 0.001, d = 0.74), with no significant difference between EM-BC and BO (P = 1.00, d = 0.001). Lastly, MM-BC resulted in a moderate, significant reduction in glycaemic variability across the 6 h experimental period compared with BO (–4.4%; P = 0.008, d = 0.56) yet the difference was trivial between EM-BC and BO (–1.1%; P = 1.00, d = 0.14). Although a second-meal effect was not found after EM-BC, the results of this study are important because they demonstrate that the timing of breakfast or the interval between the 1st and 2nd meals may be important for breakfast skipping girls. In summary, the information presented in this thesis extends the knowledge on glycaemic variability in relation to daily PA, exercise bouts and breakfast timing interventions in healthy adolescents. This thesis demonstrates an acceptable performance of FreeStyle Libre and the practicality of using this tool under free-living conditions with adolescents. This thesis provides further evidence of the potential benefit of engaging in daily MVPA and reducing sedentary time to lower glycaemic variability. In addition, thirty-minute bouts of MIE and HIIE reduced postprandial glycaemic response to a breakfast meal consumed in close proximity to exercise, but not to lunch or dinner, suggesting a short-term effect of exercise on glycaemia. Finally, consuming breakfast in the mid-morning (e.g., during the school break) may promote the metabolic health of girls who habitually skip breakfast by moderating the post-lunch glycaemic response.8 0