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Title: Effect of polyphenols on glucoregulatory biomarkers, blood pressure and lipid profile in overweight and obese subjects
Author: Al Moosawi, Suzana
ISNI:       0000 0004 2722 7854
Awarding Body: Queen Margaret University
Current Institution: Queen Margaret University
Date of Award: 2010
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This thesis describes a series of in vitro, animal and humans studies conducted with the aim of investigating the effect of polyphenol-rich green coffee bean extract (GCBE) and dark chocolate (DC) on biomarkers of glucose metabolism, lipid profile and blood pressure (BP) in overweight and obese individuals. Green coffee and Theobroma cacao bean extracts were found to be rich in polyphenols and to act as effective free radical scavenging compounds in vitro. A potential role for GCBE in inhibiting pancreatic lipase was identified in vitro. Preliminary human studies revealed a differential effect of GCBE and DC on fasting glucose, total cholesterol, BP and urinary glucocorticoids. Accordingly, consumption of 200mg GCBE containing 90mg chlorogenic acid (CGA) twice daily for 14 days by healthy overweight and obese volunteers reduced systolic BP (P=0.043), urinary free cortisone (P=0.0015) and waist circumference (-0.78cm; P=0.013) but raised salivary cortisone (P=0.042) without significantly affecting capillary fasting glucose, total cholesterol or urinary antioxidant excretion (P>0.05). The ability of CGA to differentially regulate cortisol metabolism was further highlighted in male C57BL6 mice wherein daily administration of a diet containing 0.15% CGA for 17 days marginally increased cortisol in kidney (P=0.108; eta2=0.26) and reduced hepatic cortisol (P=0.219; eta2=0.14). In the preliminary single-blind randomised cross-over DC study, 2-week consumption of 20g DC containing 500mg or 1000mg polyphenols by overweight and obese individuals produced equal reductions in capillary fasting glucose, systolic and diastolic BP. This was further confirmed by the long-term placebo-controlled trial wherein ingestion of 20g DC (500mg polyphenols) for 4 weeks reduced fasting glucose (P=0.028), insulin resistance (P=0.005), systolic (P=0.020), diastolic BP (P=0.008) and improved insulin sensitivity (QUICKI, P=0.04; revised-QUICKI, P=0.026) and urinary antioxidant capacity (total phenolics, P=0.046; ferric-reducing capacity, P=0.048) without significantly affecting lipid profile (P>0.05). A particular contribution of the main study is the finding that overweight and obese individuals respond more effectively to polyphenol-rich DC, compared to lean individuals, but more adversely to polyphenol-deficient placebo. The latter was marked by the rise in fasting insulin, insulin resistance and salivary cortisol. In conclusion, this thesis supports a role for polyphenol-rich GCBE and DC in counteracting overweight and obesity-related complications. The role of GCBE and CGA in modulating glucocorticoid metabolism emerges as a novel and potentially relevant field of research to the prevention of overweight and obesity-related complications.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Dietetics, Nutrition and Biological Sciences