Year

2009

Degree Name

Doctor of Philosophy

Department

School of Health Sciences, Faculty of Health and Behavioural Sciences

Abstract

Making claims on the health effects of foods currently presents major challenges to nutrition science. As a case in point, oat β-glucan has been shown to deliver a number of health benefits, including an ability to lower cholesterol levels as well as reducing glucose and insulin responses to a meal. These physiological functions are related to the viscosity and solubility of the β-glucan, with the viscosity a function of concentration and molecular weight. Further, despite epidemiological evidence that high fibre diets are associated with lower levels of overweight and obesity in populations, and experimental evidence that fibre will “make you feel fuller for longer”, there is little evidence linking specific fibres with weight control. Changes to regulations governing health claims in Australia and New Zealand are currently under review, and while they reflect European and other regional positions in allowing claims for β-glucan and cholesterol, they do not address other health benefits such as weight loss. This thesis provides a novel approach to evidence based research in food by combining studies in food science, acute meal tests and longer term dietary interventions. The hypothesis examined in this thesis is that overweight individuals following a nutritionally-balanced, energy-restricted diet including oat β-glucan will experience increased satiety and lose more weight than if they followed the same diet without the added β-glucan. Product development studies examined the effects of extrusion on the important physical attributes of β-glucan included in a ready-to-eat cereal product. It did not prove difficult to produce a cereal that maintained β-glucan at high molecular weight (>1 million) and was viscous at high concentration (up to 5g β-glucan/cereal serve). Extrusion improved solubility which means the effects of downstream processing in this manner are likely to improve the physiological effects of β-glucan in cereals. Results of a meal-test study with fourteen subjects found that increasing doses of β- glucan up to 5.5 g, decreased insulin levels (P=0.011) and increased subjective satiety measured by visual analogue scales (P=0.039). Increasing doses of β-glucan were correlated with increased plasma concentrations of cholecystokinin (CCK) and peptide Y-Y (PYY) (R2=0.970 and 0.994 respectively). Food intake at a subsequent meal was decreased with inclusion of β-glucan in the earlier test meal, although the differences were not statistically significant. A 3-month randomised controlled trial of 66 overweight women was then conducted to investigate the effects of two different doses of β-glucan (5-6g or 8-9g) on weight loss within an energy-restricted regimen. Outcome measures included weight loss and markers of appetite regulation (hormones) as well as changes in metabolic variables related to cardiovascular disease. All groups lost weight (approximately 5% of body weight) and showed a reduced waist circumference (P

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