The effect of nutrition on risk factors for coronary heart disease

Abstract

Motivation: Cardiovascular disease (CVD), including coronary/ischaemic heart disease, angina pectoris and stroke, is one of the leading causes of mortality and morbidity world-wide as well as in South Africa. It is predicted that in 2020 CVD will become the most important cause of death and morbidity in developed and developing countries. Numerous factors can contribute to the development of CVD. These factors can be divided into lifestyle or behavioural and other non-modifiable risk factors that may result in various physiological and metabolic risk factors. Dietary intervention, together with other lifestyle changes, form an important part of the management of some of these risk factors. There are, however, still some uncertainties, inconsistencies and a lack of data in the literature regarding the effects of some dietary factors on various CVD risk factors. Objectives: The main objective of this study was to examine the effects of a few dietary factors on the relevant CVD risk factors about which controversies still exist in the literature. The dietary factors were alcohol intake, sugar (sucrose) intake, lecithin and dietary fibre. The dietary fibre was obtained from two sources, namely wheat bran and dry beans that were tested in two new products or "functional foods" (high fibre baked product and extruded dry bean product). To attain this main objective, the following objectives for each of the five separate studies were stated: To describe the mean alcohol consumption and its relationships with serum lipoproteins and blood pressure in white South Africans. These subjects participated in the VIGHOR study, a randomised cross-sectional epidemiological study; to investigate the relationship between added sugar consumption and body mass index (BMI) and the effects of added sugar consumption on the macro and micronutrient intake patterns in the same white South Africans who participated in the VIGHOR study; to examine the effects of lecithin on serum lipoprotein, plasma fibrinogen and macro molecular protein complex (MPC) levels in a double-blind study which controlled for possible indirect effects; to determine what the effects of high fibre (wheat bran) vs low fibre meals would be on postprandial serum lipoprotein and plasma factor VII coagulant activity responses in a randomised cross-over study; and to examine the effects of the inclusion of extruded dry beans in the diet on serum lipoprotein, plasma fibrinogen, plasma viscosity and plasminogen activator inhibitor (P All) levels in a randomised controlled cross-over study. Methodology: This thesis consists of three published papers and two manuscripts submitted for publication. The reader is referred to the abstracts at the beginning of each separate paper in chapters 3-7, for a description of the subjects, study design and analytical methods used in each study. To examine the relationships between alcohol and sugar intake with CVD risk factors, data from a cross-sectional epidemiological study, the VIGHOR study, were used. These relationships were estimated by using partial correlations to control for possible confounding factors. To examine the effects of lecithin, wheat bran and extruded dry beans, nutrition interventions were performed under controlled circumstances on homogenous groups of men. Effects on both the lipoprotein and haemostatic risk factors were analysed by means of standard methods. Results and conclusions of the individual studies: Analyses of the VIGHOR data showed that alcohol consumption had a positive effect on high density lipoprotein cholesterol (HDL-C) levels in both men and women. A small negative effect on blood pressure was, however, observed in men. The consumption of alcohol for cardioprotective purposes is therefore not encouraged, since it can be associated with both risk and protective effects against CVD. Because alcohol forms part of many South Africans lifestyle, for those who do consume alcohol, except for individuals with alcohol-related disorders, light to moderate consumption together with management of other CVD risk factors can be recommended. No relationship between daily added sugar intake and BMI was observed in the VIGHOR subjects. Sugar intake was negatively associated with fat intake. In the men, sugar intake did not constitute a major risk for nutrient inadequacy. The women, probably because of their low energy intakes, were, however, more prone to nutrient inadequacies with increased sugar intake, especially with regard to dietary fibre, iron, magnesium, copper, thiamine and vitamin B6. Avoidance or restriction of sugar consumption will probably not correct an already nutrient-inadequate diet and may even lead to an increased intake of fat. It is suggested that the message regarding sugar consumption to this population and others moving towards "westernised" diets, should be that added sugars can be consumed in moderation. Women with low energy intakes should be cautious not to displace nutrientand fibre-rich foods with foods containing large amounts of sugar. In the study which examined the effects of soya bean lecithin, lecithin treatment caused significant increased plasma linoleic acid levels, indicating that compliance to the treatment was obtained. Lecithin treatment, however, had no independent effects on serum lipoprotein, plasma fibrinogen of MPC levels in these hyperlipidaemic men. The results therefore suggest that the daily intake of 20g lecithin cannot be used as a hypolipidaemic agent. High fibre meals caused more gradual serum triglyceride (TG) and retinyl palmitate (marker for chylomicrons and their remnants) response curves compared to low fibre meals in a postprandial study in normolipidaemic men. This resulted in significantly higher levels of TG and retinyl palmitate and lower HDL-C levels after three hours. Before final conclusions regarding this possible detrimental effect of fibre can be made, these findings need to be confirmed by other postprandial studies. The possible mechanisms responsible for these findings need to be further examined. A positive finding from this study was that the intakes of normal physiological amounts of fat in a meal, as used in this study (30.5g fat/meal) did not activate plasma factor VII, even though serum TG increased significantly. The mean intake of extruded dry beans per day was 91.9g (83 .5%), indicating relatively good compliance with the experimental intervention. Extruded dry beans had no effects on serum lipoproteins, plasma fibrinogen and viscosity levels, but indicated a positive effect on P AI-1. P AI-1 levels were significantly lower after the intake of extruded dry beans compared to the control period that might have beneficial effects on the fibrinolytic system. Combined discussion: A critical evaluation of the recommendations based on the results from the five separate studies indicated that they were all compatible with the latest consensus dietary guidelines for the management of the common hyperlipidaemias in South Africa. However, the study indicated that more research regarding the postprandial effects of dietary fibre on the lipid metabolism is needed. The study further contributed to the potential benefits of dietary treatment on haemostatic factors. It also stresses the importance of more research in this field before meaningful dietary guidelines can be made for the management of hypercoagulability. An important contribution of this study lies in the development of capacity to evaluate the effects of new "functional foods" ( the high fibre baked product and the extruded dry bean product) on metabolic risk factors for CVD in a scientifically responsible way in well-designed controlled studies before health claims regarding these food products can be made.