Insulin resistance is a characteristic feature of type 2 diabetes mellitus (DM ) and is associated with increased cardiovascular disease. This thesis presents one randomised controlled trial and two cross-sectional analyses, examining the influence of fruit and vegetable consumption and endocrine factors (se~ hormone binding globulin and vitamin D) on insulin resistance. After a 4 week diet of 1-2 portions fruit and vegetables per day, 105 overweight (8MI 27 - 35kg/m2), nondiabetic subjects at elevated cardiovascular disease risk (>20% 1 O-year CVD risk), were randomised to follow a diet of 1-2,4 or 7 or more portions fruit and vegetables per day for the 12-week intervention. Insulin resistance was assessed pre and post intervention using a two-step euglycaemic hyperinsulinaemic clamp. In the cross-sectional analyses, baseline clamp assessments were correlated with sex hormone binding globulin concentration and with vitamin D concentration respectively. Increasing fruit and vegetable consumption was not associated with a change in insulin resistance. Sex hormone binding globulin concentration was inversely correlated with insulin resistance, independent of androgen concentrations and adiposity in the subgroup of 28 postmenopausal women. No association was demonstrated in men. Vitamin D was not associated with insulin resistance. In overweight people at high risk of cardiovascular disease, increased fruit and vegetable intake has no effect on insulin resistance. Weight was maintained in our study and it is possible that alterations in weight have a greater impact on insulin resistance than dietary composition. We suggest that beneficial effects of fruit and vegetable consumption are not mediated by change in insulin resistance. We demonstrate an inverse association between sex hormone binding globulin concentration and insulin resistance, primarily peripheral insulin resistance. We demonstrate no association between vitamin D and insulin resistance and suggest that an association between vitamin D and type 2 DM may be mediated via effects on insulin secretion.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:677846 |
| Date | January 2014 |
| Creators | Wallace, I. R. |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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