- Title
- Do long chain omega-3 polyunsaturated fatty acids modulate dietary fat induced changes in plasma lipid and lipoprotein profiles?
- Creator
- Dias, Cintia
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2016
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The consumption of foods rich in saturated fats has been associated with elevated blood lipid levels and consequently with risk for numerous chronic diseases, such as coronary heart disease. However, understanding the effects of replacing saturated fat in the diet is complex, and the health effects of reducing saturated fat consumption clearly depend on what substitutions are made. Furthermore, studies using animal models have demonstrated that dietary saturated fats raise triglyceride levels only when the diet is deficient in omega-3 polyunsaturated fatty acids (n-3PUFA). The n-3PUFA are known for their potential to help in managing hyperlipidaemia for the prevention of coronary heart disease, as well as for their anti-inflammatory, anti-arrhythmic and anti-aggregatory potential. In addition, research in human and animal models has shown competition for important enzymes in the metabolism of omega-6 polyunsaturated fatty acids (n-6PUFA) and n-3PUFA, with high consumption of n-6PUFA leading to an increase in their metabolism at the expense of n-3PUFA. This leads to an increased production of n-6PUFA derived eicosanoids, which are pro-inflammatory and pro-aggregatory, in contrast with those derived from n-3PUFA, which are less inflammatory and aggregatory. Therefore, we hypothesised that consumption of saturated fats, would not adversely influence coronary heart disease risk factors (blood lipid levels, lipoprotein profiles, platelet aggregation and inflammation) when the diet was balanced with an adequate intake of n-3PUFA. Moreover, we hypothesized that the health benefits obtained with the consumption of n-3PUFA would be maximised by including foods rich in saturated fat and reducing the consumption of vegetable oils (rich in n-6PUFA) in the diet. Our first aim, addressed in chapter 3, was to establish the basis for our hypothesis, analysing the literature on saturated fatty acids to identify the contradictions in the literature to date and to highlight the gaps in knowledge gained from previous interventional and epidemiological studies. We have observed that although many studies have associated saturated fatty acids with hyperlipidaemia and cardiovascular disease risk factors, there is still much contradiction on the subject with not all studies finding the same association. The key studies relating saturated fat consumption and heart health made no mention about the presence or absence of n-3PUFA as a possible confounding factor. This may have been due to the lack of knowledge about the existence of n-3PUFA or an inability to determine n-3PUFA concentration in most of the early studies. Therefore the missing link in the research on cardiovascular disease risk and dietary fats could be an ignorance of the interactions between different dietary fats and the effect of this interaction. In Chapters 4a and 4b we aimed to determine if LCn-3PUFA and the other dietary fats interact during digestion, absorption, re-esterification into triglycerides and assembly into chylomicrons to modulate circulating lipid levels postprandially. In a randomised cross-over design, we investigated the effect of feeding meals rich in either saturated fatty acids or n-6PUFA in conjunction with LCn-3PUFA on plasma lipid (triglycerides and total, low density lipoprotein and high density lipoprotein cholesterol) and fatty acid levels. The postprandial lipemic response and fatty acid kinetics were similar after the consumption of both meals and suggest that the competition between n-3 and n-6PUFA may be a longer term phenomenon, not just a postprandial effect. The aim of Chapter 5 was then to determine if there were interactions between LCn-3PUFA and other dietary fats in the longer term (6 weeks). Therefore, in a randomized parallel design intervention we investigated the longer-term effects of LCn-3PUFA supplementation in subjects consuming diets enriched in either saturated fatty acids or n-6PUFA, on blood lipid profiles and on the incorporation of fatty acids into plasma and erythrocyte lipids. Long chain omega-3 polyunsaturated fatty acids were incorporated to a greater extent into the plasma and erythrocyte lipids of subjects consuming the saturated fat rich diet compared to the n-6PUFA rich diet, although total and low density lipoprotein (LDL) cholesterol were also increased. Plasma samples of the subjects who completed the intervention in chapter 5 were then further analysed in chapter 6 for lipoprotein profiles, with the aim of determining if the increase in plasma cholesterol levels was due to changes in the lipoprotein particle concentration or size. The increase in LDL cholesterol was due to an increase in the less atherogenic, large, buoyant LDL particles rather than the small, dense LDL particles. In chapter 7, the aim was to determine if pre-supplementation rather than co-supplementation with LCn-3PUFA would improve the effect of the major dietary fat groups on plasma lipids and lipoprotein profiles. Therefore, in a randomized parallel design clinical intervention, we examined the effect of increasing the omega-3 index of subjects before randomizing them to a diet rich in either saturated fatty acids or n-6PUFA. The diet rich in saturated fatty acids increased, while the diet rich in n-6PUFA decreased, total and LDL cholesterol, independently of LCn-3PUFA supplementation. However, the saturated fatty acid rich diet caused a further increase in plasma and erythrocyte LCn-3PUFA compared to the n-6PUFA rich diet. In conclusion, the results presented in this thesis demonstrate that the background dietary fat is a determinant of the degree of incorporation of LCn-3PUFA into plasma and tissue lipids. The consumption of a saturated fat rich diet did indeed cause an increase in plasma cholesterol levels. However, the rise in circulating cholesterol levels following saturated fat consumption is accompanied by an increase in the less atherogenic LDL particle size, when the LCn-3PUFA status is adequate, which is likely to reduce the detrimental effects. In addition, there was a concurrent increase in incorporation of LCn-3PUFA into plasma and erythrocytes, which may have benefits, independent of cholesterol or blood lipids. Hence, this thesis paves the way for further research to examine the impact of increased plasma and tissue LCn-3PUFA levels as a result of saturated fat consumption with adequate LCn-3PUFA intakes, on cardiovascular health risk indicators, such as inflammation, hypertension, platelet aggregation and endothelial function.
- Subject
- postprandial lipemia; LCn-3PUFA; n-3PUFA; n-6PUFA; saturated fat; lipoprotein profiles; plasma lipids; fatty acids; NMR
- Identifier
- http://hdl.handle.net/1959.13/1313736
- Identifier
- uon:22630
- Rights
- Copyright 2016 Cintia Dias
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT01 | Thesis | 2 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 314 KB | Adobe Acrobat PDF | View Details Download |