Abstract
Epidemiological evidence suggests that those individuals who consume greater quantities of whole grain are at reduced risk of cardiovascular disease (CVD). The current body of work set out to investigate this relationship via a programme of dietary intervention trials. In order to develop a novel and robust protocol a range of markers of cardiovascular risk were sought. Pulse wave velocity (PWV) is an established independent marker of CVD risk but was lacking in reproducibility data. Therefore initial method development focused on examining the PWV responses of a cohort reflecting that of the planned targeted population groups (i.e. CVD risk). Within a cohort of men at varying levels of CVD risk (n=8), it was clear that PWV does not change significantly over time when participants were following an habitual daily routine (4-6 weeks duration), nor is it significantly affected by acute metabolic challenges from exercise or the postprandial state. With the degree of variation below 10% for all scenarios, the whole-body measure of vascular- health was proven to be a robust marker of PWV which is not unduly influenced by possible confounding factors. The intervention phase of the research encompassed three distinct studies. The High Risk Study (Chapter 4) was a randomised, controlled, parallel dietary intervention study In a cohort of individuals at an increased risk of CVD due to obesity (n=21, aged 47.6+/-12.0years, BMI 28.9+3. 1kg/m2), it was examined whether increasing the amount of whole grain consumed per day by 48g conferred benefits to health. The study design examined the difference between the effects of consuming whole grain versus the equivalent amount of milled grain, which in turn was compared to an isocaloric control. A unique system of bread rolls were used to deliver a controlled amount of intervention ingredient in a timely manner, participants were required to consume two rolls per day (24g of whole or milled grain per roll) for eight weeks. Focussing on arterial stiffness (via the measurement of PWV) and the reported inflammatory response associated with the establishment of atherosclerosis, no significant beneficial effect was found post-intervention for either the whole or milled grain. Similarly no positive changes in lipid profile, post-prandial glycaemic control or anthropometric outcomes were identified. To understand the possible benefits of whole grain consumption within the wider population, The Low Risk Study (Chapter 5) replicated the High Risk Study design in a cohort of young men (n=25, aged 22.8+/-2.0years, BMI 23.5+3.0) at low risk of CVD. Once again no beneficial effects on lipid profile, fasting glycaemic control or anthropometric measures were found following wholegrain supplementation. However, a significant reduction in central PWV (carotid-femoral) of 0.3m/s (from 5.8m/s to 5.5m/s, p=0.02) was detected indicating possible long-term, beneficial changes within the structural function of the arteries. Finally study 3, the Cross-Over Study (Chapter 6) carried through the same outcome measures to a comparative investigation of 2 key components of whole grains, wheat fibre and inulin versus control. The study cohort (n=10) were at increased risk of CVD due to obesity (aged 39.8+/-9.6years, BMI 30.2+3.0kg/m2) and consumed 15g of the active ingredient a day for 28 days per study leg. No significant changes within or between supplement (inulin, wheat fibre or control) were found for arterial stiffness and blood flow, inflammatory markers, lipid profile or anthropometric markers. For glycaemic control, a small significant reduction in glucose area under curve (AUC) was detected following wheat fibre supplementation when expressed as percentage change from baseline and compared to the control. The key point of the SLOWCARB programme is that it is the first known body of research within the current literature to demonstrate the successful use of an 'intervention delivery system' via the use of specially-made bread rolls containing a specified amount of whole grain or fibre. Commonly within previous dietary intervention studies, food replacement strategies were implemented which often resulted in a high level of dietary modifications. Despite no clear pattern of effect from whole grains (and their constituent fibres) being detected, some positive outcomes have been achieved. Therefore additional research focussing on the effects of whole grains on vascular health is justified.