Plants synthesize and store oil, mostly as triacylglycerols (TAG), in seeds that is transcriptionally controlled by WRINKLED1 (WRI1), an APETALA2 (AP2) transcription factor. Among the four Arabidopsis WRI paralogs, WRI2 is nonfunctional, while the others are expressed in a tissue-specific manner. Additionally, two rate-limiting enzymes, diacylglycerol acyltransferase (DGAT) and phospholipid diacylglycerol acyltransferase (PDAT) catalyze the terminal step in TAG assembly and contribute to oil accumulation. Avocado (Persea americana) mesocarp, a non-seed tissue, accumulates significant amounts of TAG (~70% by dry weight) enriched with heart-healthy oleic acid. The oil accumulation stages in mesocarp coincide with the high expression of PaWRI2, along with PaWRI1, PaDGAT1, and PaPDAT1. The strong preference for oleic acid demonstrated by the avocado mesocarp TAG biosynthetic machinery represents lucrative biotechnological opportunities, yet functional implication of these genes is not explored. Using structural analyses, we showed that PaWRI2 is a relatively stable protein, has a single intact AP2 DNA-binding domain, and has different C-terminal properties compared to its ortholog in Arabidopsis. Through transient expression, we demonstrated that PaWRI2 is functional and drives TAG accumulation in Nicotiana benthamiana leaves, unlike Arabidopsis WRI2. Additionally, co-infiltration of PaWRI2, along with PaWRI1, PaDGAT1, and PaPDAT1 further increased the lipid content and oleic acid levels in ‘benth’ leaves. Quantitative real-time PCR (qPCR) analyses of >46 fatty acid biosynthetic pathway genes revealed that several were distinctly up- or down-regulated by the expression of PaWRI2 and PaWRI1. Further yeast-one-hybrid assay showed a unique characteristic of PaWRI2 being autoregulated and by PaWRI1. Also, both the proteins could bind to AW-box promoter elements in specific avocado genes. Deletion of the C-terminally-located ordered region in both the proteins further improved the lipid content with an altered composition in the leaf tissue. In conclusion, avocado WRI2 is capable of transactivation of fatty acid biosynthesis genes and TAG accumulation, synergistically with DGAT1 and PDAT1, in non-seed tissues. This study provides a functional role for WRI2 in a basal angiosperm species that is likely lost in modern angiosperms and thus provides basis for mechanistic differences in the transcriptional regulation of lipid biosynthesis among different plant species and between seed and non-seed tissues.

Producing biodiesel from triacylglycerol (TAG) generates glycerol as a byproduct which could be recycled and used to grow the oleaginous yeast Rhodotorula glutinis. R. glutinis has the ability to produce up to 70% of its weight in the form of TAG. This study is designed to determine the effects of glycerol on the TAG and fatty acids produced by R. glutinis. After 24 hrs, R. glutinis cultured on medium containing dextrose, xylose, glycerol, dextrose and xylose, xylose and glycerol, or dextrose and glycerol accumulated 16, 12, 25, 10, 21, and 34% TAG on a dry weight basis, respectively. The fatty acids derived from R. glutinis were mostly saturated, however, cells cultivated on glycerol alone had the highest degree of unsaturated fatty acids (53%). Growth on dextrose may be enhanced by the addition of glycerol, but it cannot be determined if using glycerol as a secondary carbon substrate enhances lipid production.

Metabolic energy is most efficiently stored as triacylglycerol (TAG). This neutral lipid accumulates mainly within adipose tissues, but it can be stored and used in all types of cells. Within cells it is packed in organelles called lipid droplets (LDs). They consist of a core of neutral lipids like TAG and cholesterol esters, which is surrounded by a phospholipid monolayer that mainly consists of phosphatidylcholine (PC). Attached to or inserted into this monolayer are various proteins, mainly LD specific structural proteins or lipid metabolic enzymes. Though excess uptake of nutrition leads to lipid accumulation in all kinds of body tissues, which is accompanied by the augmentation of LDs and results in cellular dysfunction and the development of metabolic diseases, relatively little is known about the biogenesis and growth of LDs. This thesis focuses on diacylglycerol acyltransferase 2 (DGAT2), an enzyme of the TAG biosynthetic pathway, and on lyso-phosphatidylcholine acyltransferases 1 and 2 (LPCAT1 and LPCAT2), both enzymes of one of the PC biosynthetic pathways called Lands cycle. The data presented in this thesis show that these enzymes can localize to LDs and that they actively synthesize TAG and PC at the surface of LDs. While the LPCATs reside on LDs independent from the nutrition status of the cell, DGAT2 accumulates on LDs upon excess availability of oleic acid. DGAT2, LPCAT1 and LPCAT2 differ in their structure from other iso-enzymes that catalyze the same reactions. This thesis shows that they exhibit a monotopic conformation and that they contain a hydrophobic stretch that presumably forms a hairpin. This topology enables them to localize to both a phospholipid bilayer like the membrane of the endoplasmic reticulum and to a phospholipid monolayer like the surface of LDs. The different biophysical properties of the structures of iso-enzymes might be responsible for their subcellular localization and the formation of distinct TAG or PC pools that are destined for different purposes. This would explain, why the iso-enzymes are often not able to replace each other. Knock-down and overexpression experiments performed in this thesis show that the activity of LPCAT1, LPCAT2 and DGAT2 influence the packaging of lipids within LDs. Knock-down of LPCAT1 and LPCAT2 leads to an increase in LD size without concomitant increase in the amount of TAG. Combined with the finding that the profile of the PC species of the LD surface reflects the substrate preferences of LPCAT1 and LPCAT2, the results suggest that these enzymes are responsible for the formation of the LD surface. Therefore, the increase in LD size upon LPCAT1 and LPCAT2 knock-down results from an adjustment of the surface-to-volume ratio in response to reduced availability of surface lipids. The connection between LPCATs and LD size was corroborated in the model organism Drosophila melanogaster. Three different knockout fly strains of the Drosophila homologue of LPCAT1 and LPCAT2, CG32699, exhibit enlarged LDs in the fat body of the L3 larvae. Furthermore, the data presented suggest that the morphology of LDs is important for the secretion of stored lipids. The reduction of LPCAT1 in liver cells leads to a reduction in lipoprotein particle release. This was shown by measuring the amount of released apolipoproteinB with two different methods, by measuring the release of lipids and by quantification of the amount of released hepatitis C virus, which is known to rely on LD interaction for replication and on lipoprotein particles for cellular release. DGAT2 is recruited to LDs upon excess availability of oleic acid and its overexpression leads to the formation of many, but relatively small LDs. Here, it is shown that DGAT2 interacts with acyl-CoA synthetase ligase 1 (ACSL1), an enzyme that catalyzes the activation of free fatty acids with Coenzyme A. This interaction does not influence the stability of DGAT2 nor does it seem to affect lipid synthesis. Nevertheless, it shows an influence on lipid packaging in LDs. While overexpression of DGAT2 results in the appearance of smaller LDs, overexpression of ACSL1 leads to an increase in LD size. Coexpression of ACSL1 and DGAT2 reverses the phenotypes obtained by single overexpression and normalizes the mean LD diameter to values observed at normal conditions. In conclusion, this thesis shows that LDs are able to synthesize the components of their core and their surface, which underlines their independent function in metabolism. Additionally, the results show that LDs can grow by local synthesis and that the responsible enzymes exhibit a monotopic membrane topology, which might be crucial for LD localization. Furthermore, the obtained data suggest that the localization and the ratio between different enzyme activities influence the packaging of lipids and affects lipid secretion and therefore impact the whole body lipid metabolism.

Globally, cardiovascular disease (CVD) is a major cause for morbidity and mortality. Exaggerated postprandial lipaemia has been implicated in the development of atherosclerosis, and by lowering postprandial triacylglycerol (TAG) concentrations, atherogenic progression may be delayed. Many studies have revealed that exercise, in particular acute exercise, can attenuate postprandial TAG concentration. Most of this evidence relates to studies conducted in Western participants. South Asians are a population predisposed to CVD, and their adverse lipid profiles and physical inactivity may be among the underlying reasons. Hence, the studies described in this thesis examined the potential of acute bouts of exercise to favourably modify postprandial lipaemia and other CVD risk markers in young, healthy, South Asian men. The first experimental study described in this thesis compared the effect of 60 minutes of brisk walking on postprandial TAG concentration in 15 South Asian and 14 White European men. Trials were conducted over two days with exercise (or rest) taking place on day 1 and postprandial testing on day 2. A key finding from this study was that postprandial TAG, glucose and interleuklin-6 (IL-6) concentrations were elevated in South Asian compared with White European participants after consumption of high fat meals. This study also revealed a non-significant trend for brisk walking to reduce postprandial TAG concentrations in response to high fat meals in both groups. The second experimental study reported here examined the effect of 60 minutes of treadmill running at 70% of max on postprandial lipaemia and other CVD risk makers on the next day in 10 South Asian and 10 White European men. A significant main effect of trial was shown for postprandial TAG, IL-6 and soluble intercellular adhesion molecule-1 (sICAM-1), showing that TAG and IL-6 concentrations were lower on the exercise trial while sICAM-1 concentrations were higher on the exercise trial. In addition, ethnic group differences were observed for postprandial TAG, glucose and insulin concentrations indicating higher values in South Asians than White Europeans. A significant trial by group interaction effect was also observed for TAG, indicating a greater decrease after exercise in the South Asian men than the European men. In the third experimental study in this thesis the effect of 30 minutes of treadmill running on one day was compared with running for 30 minutes on three consecutive days in 11 South Asian men with regards to postprandial lipaemia. Neither a single bout of running nor three consecutive days of running influenced postprandial TAG in response to high fat meals when compared with the response on a control trial. It is not clear why exercise was ineffective in reducing postprandial lipaemia in this study but possibly the energy expenditure of exercise was insufficient to elicit change. The final experimental chapter described in this thesis combined the data from the first three studies. The objective of this chapter was to enhance the sample size in an effort to clarify the effects of acute exercise and to clarify the effects of ethnic group with respect to several fasting and postprandial CVD risk markers. The key findings were: 1) fasting and postprandial TAG and postprandial glucose concentrations were significantly reduced by exercise; 2) There were significant main effects of ethnic group for fasting high density lipoprotein cholesterol (HDL-C), total cholesterol/ HDL-C, IL-6 and systolic blood pressure (SBP), indicating lower values of HDL-C and SBP and higher values of total cholesterol/HDL-C and IL-6 in South Asian participants. Additionally, there were significant main effects of ethnic group for postprandial TAG and IL-6 indicating higher values in South Asian participants. Taken together, these data indicate that South Asians have an adverse CVD risk factor profile in comparison with White Europeans and this may explain, at least in part, their elevated risk of CVD. Importantly, the data produced within this thesis show for the first time that acute bouts of exercise can be effective for lowering postprandial plasma TAG concentrations in South Asians, at least transiently. Thus, exercise has the potential to serve as a non-pharmacological medicine in South Asians.

Plant development is complex and highly regulated. Tens of thousands of genes have been sequenced for the model plant <em>Arabidopsis thaliana</em>, yet few have been functionally annotated and characterized. This thesis describes the expression analysis and characterization of four genes in <em>Arabidopsis</em>. Three of these belong to the eukaryotic translation initiation factor 5A (eIF5A) gene family, and the fourth encodes diacylglycerol acyltransferase 1 (DGAT1). Putative roles for these genes in the development of <em>Arabidopsis thaliana</em> are described. <br /><br /> eIF5A is the only known protein to contain the amino acid hypusine. It has been demonstrated previously that eIF5A acts as a shuttle protein, moving specific mRNAs from the nucleus to the cytoplasm for translation. In <em>Arabidopsis thaliana</em> (At), there are three isoforms of eIF5A, and it is clear from the present study that they each have a unique temporal and spatial expression pattern. AteIF5A-1 and -2 are up-regulated during natural senescence and wounding/pathogenesis, respectively, and it is proposed that they regulate the onset of programmed cell death during these events. AteIF5A-3 is up-regulated in elongating meristem of the root, and it is proposed that this isoform is involved in cell growth. <br /><br /> Over-expression of the individual <em>AteIF5A</em> isoforms <em>in planta</em> resulted in pleiotropic phenotypes. When <em>AteIF5A-1</em> or <em>AteIF5A-2</em> was over-expressed, the phenotypes observed were indicative of their putative roles in the translation of proteins required for programmed cell death. When <em>AteIF5A-3</em> was over-expressed, the phenotypes were indicative of a role for this protein in the regulation of cell and tissue elongation. <br /><br /> Lipid analysis of rosette leaves from <em>Arabidopsis thaliana</em> revealed an accumulation of triacylglycerol with advancing leaf senescence coincident with an increase in the abundance and size of plastoglobuli. The terminal step in the biosynthesis of triacylglycerol in <em>Arabidopsis</em> is catalyzed by DGAT1. When gel blots of RNA isolated from rosette leaves at various stages of development were probed with the <em>Arabidopsis</em> EST clone, E6B2T7, which has been annotated as DGAT1, a steep increase in DGAT1 transcript levels was evident in the senescing leaves coincident with the accumulation of triacylglycerol. The increase in DGAT1 transcript correlated temporally with enhanced levels of DGAT1 protein detected immunologically. Two lines of evidence indicated that the triacylglycerol of senescing leaves is synthesized in chloroplasts and sequesters fatty acids released from the catabolism of thylakoid galactolipids. First, triacylglycerol isolated from senescing leaves proved to be enriched in hexadecatrienoic acid (16:3) and linolenic acid (18:3), which are normally present in thylakoid galactolipids. Second, DGAT1 protein in senescing leaves was found to be associated with chloroplast membranes. These findings collectively indicate that DGAT1 plays a role in senescence by sequestering fatty acids de-esterified from galactolipids into triacylglycerol.

Triacylglycerols (TAGs) are stored in variable amounts (1-90 % by dry weight) in seed and non-seed tissues of various plant species. We analyzed the deep transcriptional profiling data obtained for eight species (brassica, castor, nasturtium, euonymus, oil palm, date palm, and avocado), to gain insights into tissue- and species-specific regulation and biosynthesis of TAG in plants. In all tissues analyzed, an increased expression was noted for genes mostly associated with fatty acid biosynthesis in plastid, but much less increase in those for TAG assembly in the endoplasmic reticulum. In most oil-rich tissues, transcripts associated with hexose metabolism in plastid also showed higher expression, relative to cytosol; this is likely associated with the need for high pyruvate flux directed toward plastid fatty acid synthesis. Additionally, expression of WRINKLED1 transcription factor, a regulatory element associated with oil biosynthesis in seed and non-seed tissues of monocot and dicot plants, was observed in most oil-rich tissues. Transcripts for other regulatory factors that are candidates associated with TAG synthesis in seed and non-seed tissues are also identified. In summary, our studies point to distinctive modes of regulation of fatty acid biosynthesis and TAG assembly that are conserved in both seed and non-seed oil-rich plants.

Plant development is complex and highly regulated. Tens of thousands of genes have been sequenced for the model plant <em>Arabidopsis thaliana</em>, yet few have been functionally annotated and characterized. This thesis describes the expression analysis and characterization of four genes in <em>Arabidopsis</em>. Three of these belong to the eukaryotic translation initiation factor 5A (eIF5A) gene family, and the fourth encodes diacylglycerol acyltransferase 1 (DGAT1). Putative roles for these genes in the development of <em>Arabidopsis thaliana</em> are described. <br /><br /> eIF5A is the only known protein to contain the amino acid hypusine. It has been demonstrated previously that eIF5A acts as a shuttle protein, moving specific mRNAs from the nucleus to the cytoplasm for translation. In <em>Arabidopsis thaliana</em> (At), there are three isoforms of eIF5A, and it is clear from the present study that they each have a unique temporal and spatial expression pattern. AteIF5A-1 and -2 are up-regulated during natural senescence and wounding/pathogenesis, respectively, and it is proposed that they regulate the onset of programmed cell death during these events. AteIF5A-3 is up-regulated in elongating meristem of the root, and it is proposed that this isoform is involved in cell growth. <br /><br /> Over-expression of the individual <em>AteIF5A</em> isoforms <em>in planta</em> resulted in pleiotropic phenotypes. When <em>AteIF5A-1</em> or <em>AteIF5A-2</em> was over-expressed, the phenotypes observed were indicative of their putative roles in the translation of proteins required for programmed cell death. When <em>AteIF5A-3</em> was over-expressed, the phenotypes were indicative of a role for this protein in the regulation of cell and tissue elongation. <br /><br /> Lipid analysis of rosette leaves from <em>Arabidopsis thaliana</em> revealed an accumulation of triacylglycerol with advancing leaf senescence coincident with an increase in the abundance and size of plastoglobuli. The terminal step in the biosynthesis of triacylglycerol in <em>Arabidopsis</em> is catalyzed by DGAT1. When gel blots of RNA isolated from rosette leaves at various stages of development were probed with the <em>Arabidopsis</em> EST clone, E6B2T7, which has been annotated as DGAT1, a steep increase in DGAT1 transcript levels was evident in the senescing leaves coincident with the accumulation of triacylglycerol. The increase in DGAT1 transcript correlated temporally with enhanced levels of DGAT1 protein detected immunologically. Two lines of evidence indicated that the triacylglycerol of senescing leaves is synthesized in chloroplasts and sequesters fatty acids released from the catabolism of thylakoid galactolipids. First, triacylglycerol isolated from senescing leaves proved to be enriched in hexadecatrienoic acid (16:3) and linolenic acid (18:3), which are normally present in thylakoid galactolipids. Second, DGAT1 protein in senescing leaves was found to be associated with chloroplast membranes. These findings collectively indicate that DGAT1 plays a role in senescence by sequestering fatty acids de-esterified from galactolipids into triacylglycerol.

The study was to investigate the changes in (1) triacylglycerol (TAG) contents and its relationship to (2) lipid synthesis- and metabolism-related enzyme activity and (3) their gene expression in cobia (Rachycentron canadum) during the fast growth period (from October 2006 to April 2007) in ventral muscle and liver in Hsiao-Lu-Chiao island in southwestern Taiwan. The crude lipid was 12% for fed diet, 30-40% for liver while 13% in February and 11% to 9% in other month for muscle. The TAG content of crude lipid was 36 % for fed diets, and from 22% (December) to 40% (February) for muscle, and from 63% (October to February) to 47% (March) for liver. Oil red-O (ORO) staining showed that TAG accumulated in muscle in February but in December in liver. Muscle TAG contents and enzyme activities and mRNA levels of GPDH and FAS increased in February. A decrease in GPDH enzyme activity and mRNA levels but an increase in PEPCK enzyme activity and mRNA levels indicate the increased supply of acetyl-CoA for fatty acid synthesis is in muscle. An increase in FATP2 mRNA levels suggest the influx of fatty acid also contributes to increased fatty acid accumulation in muscle.In liver, TAG and fatty acid contents decreased in March April but increased FAS and PEPCK enzyme activity and mRNA levels. It is possible that fatty acid synthesis is enhanced in March, but a fast transport to other organs results in a net decline in liver fatty acid contents and subsequently a decrease in TAG contents. FATP contents decreased in March-April mRNA, indicating that the influx of fatty acid in decreasing in liver in adult fish. GPDH and GAPDH were not related to lipid metabolism in liver. These data from enzyme activity and mRNA level, demonstrated that a potentially increase in acetyl-CoA via PEPCK contributes to fatty acid synthesis and GPDH-mediated synthesis of G-3-P provide the C skeleton for TAG synthesis.

The term "lipid" covers an extremely diverse range of chemical or molecular species. Lipids, defined as molecules that are sparingly soluble in water but readily soluble in organic solvents, are broadly categorized into "neutral " or "apolar" lipids, and "amphiphilic” or "polar" lipids. Neutral lipids will include simple hydrocarbons, carotenes, triacylglycerols, wax esters, sterol eaters, as wel1 as other lipids such as fatty acids, polyprenols, and sterols In which the hydrophilic function has little Impact on the overall molecular characteristics. Polar lipids include phospholipids, glycolipids, sulfolipids, some sphingolipids, oxygenated carotenoids and chlorophylls.

Motivation: The metabolic syndrome is characterized by a group of risk factors for cardiovascular disease (CVD) that includes obesity, dyslipidemia, high blood pressure, insulin resistance, glucose intolerance or non-insulin dependant diabetes mellitus, pro-thrombotic state and pro-inflammatory state. The NHANES I11 study showed the prevalence of this syndrome to be 24.0% in men and 23.4% in women in the USA. These figures translate to more than 47 million US residents having the metabolic syndrome. In the THUSA (acronym for Transition and Health in the Urbanization of South Africans) study in South Africa it was found that 12% and 28.4% of men and women, respectively, of the black population of the North West Province had three or more disturbances characterizing this syndrome. Therefore, it is evident that the metabolic syndrome is a health problem not only for developed countries but also for developing countries. As a result, this syndrome has been identified as a target for dietary therapies to reduce the risk of CVD and type 2 diabetes. Epidemiological studies have consistently demonstrated an inverse association between nut consumption and coronary heart disease (CHD) morbidity and mortality in different population groups. Nut consumption may not only offer protection against heart disease, but also increase longevity. Recently, the benefits of nuts consumption were acknowledged by the U.S. Food and Drug Administration when they approved a qualified health claim that eating nuts (1.5 ounces/day ≈ 42.8 g/day) may reduce the risk of CHD. In this regard, the most comprehensively studied mechanism involved the favourable lipid lowering effects of nuts. There is, however, a lack of data in the literature regarding the effect of nuts on the metabolic syndrome. Objective: The main objective of this study was to examine the effects of a high walnut diet and a high unsalted cashew nut diet on markers of the metabolic syndrome in humans. In order to provide a foundational body of evidence for the aforementioned, a secondary objective included conducting a systematic review that investigates the effects of nuts on the lipid profile. Methods: The main project consisted of a controlled feeding trial with a parallel, randomized controlled study design on participants having the metabolic syndrome. Sixty-four subjects having this syndrome (29 men, 35 women) with a mean (±SD) age of 45±10 y and who met with the selection criteria were all fed a 3-week run-in control diet. After this period, participants were grouped according to gender and age and then randomized into three groups, namely, those that received a controlled feeding diet including walnuts (20% energy (E), 60-100g/day; protein:carbohydrate:fat=18:42:40%E). or unsalted cashew nuts (20%E 66- 1 15g/day; protein:carbohydrate:fat=l9:44:37%E) or no nuts (protein:carbohydrate:fat=20:47:33%E) for 8 weeks. The participants' physical activity and weight were maintained for the duration of the study. For the systematic review. human intervention trials that investigated the independent effects of nuts on lipid concentrations were included. Medline and Web of Science databases were searched from the start of the database to August 2004 and supplemented by cross-checking reference lists of relevant publications. These papers received a rating based upon the methodology as it appeared in the publication. No formal statistical analysis was performed due to the large differences in study designs of the dietary intervention trials. The main outcome measures for the systematic review, were percentage differences between treatment and control groups for total blood cholesterol (TC), low-density lipoprotein cholesterol (LDLC), high-density lipoprotein cholesterol (HDL-C) and triacyglycerols (TG). Results: Regarding the main objective, we found that both the walnut and unsalted cashew nut intervention diets had no significant effect on the lipid profile, serum fructosamine, insulin, insulin sensitivity, insulin resistance, serum high sensitivity C-reactive protein, blood pressure and serum uric acid concentrations when compared to the control dict. All three groups experienced highly significant increases in serum insulin concentrations when comparing the baseline to end (P<0.05). In turn, insulin resistance increased while insulin sensitivity decreased in all three groups. Plasma glucose concentrations increased significantly in the cashew nut group compared to the control group (P<0.05). By contrast, serum fructosamine was unchanged in the cashew nut group while the control group had significantly increased concentrations of this short-term marker of glycaemic control. The literature search for the systematic review yielded 41 5 publications. After screening, 23 nut studies were included in the review with most of these studies including heart-healthy diets. The majority of the studies were short (4-6 weeks) with only one study lasting 6 months. The number of subjects in most of the studies was sufficient to study the effects on TC and LDL-C but not for HDL-C and TG. The results of three almond (50-100g/day), two peanut (35-68g/day), one pecan nut (72g/day) and four walnut (40-84g/day) studies showed convincing evidence for a lipid lowering effect of TC between 2-1 6% and LDL-C between 2- 19%, when compared to their control diets. Currently, there are indications from inadequately designed intervention studies that hazelnuts (lg/day/kg body weight) and pistachios (20%E) may have a lipid lowering effect. At this stage the evidence for macadamia nuts is less convincing. Furthermore, it is apparent that the components in nuts further reduce TC and LDL-C concentrations beyond the effects predicted by equations based solely on dietary fatty acid profiles. Conclusions: In the controlled feeding trial, subjects displayed no improvement in the markers of the metabolic syndrome after following a walnut or unsalted cashew nut diet compared to a control diet while maintaining body weight (8 weeks). Finally, we suspect that the dramatic increase in insulin resistance may have masked the protective effects of the walnut and cashew nut diets in our subjects with the metabolic syndrome Further research is warranted before a consensus can be reached. From the systematic review it was concluded that the consumption of ≈50-100g (≈1.5-3.5 servings) of nuts five or more times/week as part of a heart-healthy diet with total fat content (high in mono- and /or polyunsaturated fatty acids) of ≈ 35% of energy may significantly decrease TC and LDL-C in normo- and hyperlipidemic individuals. Recommendations: A similar nut controlled feeding trial with some form of calorie restriction, should be done on participants having the metabolic syndrome. Future research should use randomized controlled studies with larger sample sizes and longer duration to investigate the effects of nuts on HDL-C and TG concentrations. Also, studies should investigate the effects on the lipid profile of mixed nuts and those individual nuts not yet considered. In addition, the unique nutrient and non-nutrient composition of nuts requires further research in order to elucidate the possible mechanisms responsible for the LDL-C lowering effect / Thesis (Ph.D. (Nutrition))--North-West University, Potchefstroom Campus, 2005.