Alogaiel, Deema
(2025)
The impact of lifestyle factors, dietary energy restriction and religious fasting on body composition, gastrointestinal hormones and markers of health.
PhD thesis, University of Nottingham.
Abstract
Background
Intermittent fasting and dietary interventions to bring about weight-loss have received considerable attention for their potential metabolic health benefits. However, gaps still exist in understanding their effects on appetite regulation, body composition changes across different age groups, and the methodological challenges in assessing these outcomes. This thesis aimed to: 1. undertake a systematic review to examine the effect of Ramadan intermittent fasting on appetite-regulating hormones in healthy individuals (CHAPTER 3); 2. investigate relationships between lean body mass, physical activity, age, and body composition in overweight individuals with pre-diabetes (CHAPTER 4); 3. explore the impact of lifestyle factors and eating behaviours on body composition changes following an 8-week low-energy diet intervention (CHAPTER 5), and 4. validate commonly used assessment tools for dietary protein intake, body composition, and physical activity against their respective reference standards (CHAPTER 6).
Methods
1. A systematic review and meta-analysis examined 16 studies (n=664 participants) to investigate the effects of Ramadan intermittent fasting on circulating leptin, ghrelin, insulin, gastrin, glucagon-like peptide-1, peptide YY, and cholecystokinin concentrations. 2. A secondary analysis of cross-sectional data from 220 overweight and obese individuals with pre-diabetes (aged 25-70 years) from the Prevention of diabetes through lifestyle Intervention and population studies in Europe and around the World (PREVIEW) diabetes risk study to explore relationships between body mass, regional body composition (measured by Dual Energy X-Ray Absorptiometry; DXA), age and physical activity (assessed using accelerometry). 3. A secondary analysis of anthropometric, metabolic, and behavioural outcomes (including eating behaviours measured through validated questionnaires) from 221 participants (91 males, 130 females) from the PREVIEW cohort, collected before and after an 8-week low-energy diet intervention (810 kcal/day). 4. Dietary protein intake, assessed via 24-hour urinary nitrogen excretion, was compared with self-reported dietary records (n=264); body composition via bioelectrical impedance was compared with data from DXA scans (n=37), and physical activity estimation via the Baecke questionnaire was compared with accelerometry-derived time spent in sedentary and moderate/vigorous activity (MVPA).
Results
1. Ramadan intermittent fasting increased blood ghrelin concentration (3 studies; standardised mean difference (SMD) = 0.31 pg/mL, 95% CI: 0.03 to 0.60), but had no effect on leptin (12 studies; SMD = −0.11 μg/mL, 95% CI: −0.36 to 0.14), insulin (6 studies; SMD = −0.24 μU/mL, 95% CI: −0.54 to 0.02), or gastrin concentrations (3 studies; SMD = 0.23 pg/mL, 95% CI: −0.71 to 0.99), with high heterogeneity observed across leptin studies, suggesting varied individual responses. 2. In individuals with pre-diabetes, lean body mass and leg lean mass decreased with increasing age category in females, with males having greater lean leg mass compared with females across all age groups. Leg lean mass was positively associated with body weight, with physical activity only modifying this relationship in females, though in all participants, no association between leg lean mass and physical activity was observed. 3. The low-energy diet brought about substantial weight loss (median -11.3 kg) in participants, with males experiencing greater reductions in weight, lean mass (-4.5 vs -2.5 kg), and fat mass (-8.8 vs -7.3 kg) compared with females. Higher baseline dietary restraint scores were associated with greater weight loss success (R=0.276, P<0.001), while higher disinhibition predicted poorer outcomes (R=-0.173, P<0.05), with these behavioural influences differing between sexes. Baseline physical activity levels did not influence lean mass preservation or fat mass loss during the period of weight-loss. 4. The 8-week LED intervention resulted in improvements in metabolic parameters, including reduced fasting glucose, insulin, triglycerides, and C-peptide concentrations. Sex-specific responses were observed, with males showing greater reductions in fasting insulin (-25.7 pmol/L difference, P<0.001), C-peptide (-211 pmol/L difference, P<0.001), and triglycerides (-0.210 mmol/L difference, P<0.001) compared with females. Males also demonstrated larger improvements in insulin sensitivity indices (HOMA-IR and QUICKI) than females. 5. Validation studies revealed systematic differences between assessment methods: self-reported dietary protein intake differed from biomarker-derived estimates, with proportional bias between measures emerging during a weight maintenance intervention phase (overall R=0.394, P<0.001). Body composition assessed by BIA and DXA showed strong agreement between measurements (percentage body fat R=0.853, fat mass R=0.896, and fat-free mass R=0.841) supporting BIA as a practical alternative to DXA. Physical activity assessments demonstrated modest correlations between subjective and objective measures (R=0.320 for MVPA) reflecting the different aspects of physical activity being assessed by each tool.
Conclusion
Increased circulating ghrelin, reported during Ramadan fasting, may drive a stimulation of appetite.
Cross-sectional analysis revealed age-related differences in lean mass, with lower lean mass observed among older participants, particularly females. This pattern underscores the importance of women maintaining physical activity as they age to preserve muscle mass. The low-energy diet intervention demonstrated efficacy in reducing body weight and improving metabolic health, with notable sex-specific responses in insulin sensitivity and lipid metabolism, alongside baseline eating behaviours serving as important predictors of weight loss success. The method validation studies provided methodological insights for future research in nutritional epidemiology and clinical practice.
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