The effect of test meal monounsaturated fatty acid: saturated fatty acid ratio on postprandial lipid metabolism

Effects of diets rich in ghee or olive oil on cardiometabolic risk factors in healthy adults: a two-period, crossover, randomised trial

This study aimed to evaluate the cardiovascular health-related effects of consuming ghee in the usual diet. Thirty healthy men and women were studied in a free-living outpatient regimen. The participants were instructed for the isoenergetic inclusion of ghee or olive oil in their diets for 4 weeks using a randomised crossover design. At the end of run-in (baseline), 2-week wash-out and interventions, fasting blood samples were drawn. In addition, 2-h postprandial blood samples were collected after ingestion of a meal containing olive oil or ghee at week 4 of each dietary intervention. Body weight was not different between the two interventions. Compared with the olive oil, the diet with ghee increased fasting plasma apo-B (apo B) (0·09, 95 % CI 0·02, 0·17 g/l, P = 0·018), non-HDL-cholesterol (non-HDL-cholesterol) (0·53, 95 % CI 0·01, 1·05 mmol/l, P = 0·046) and LDL-cholesterol did not differ significantly between diet groups (0·29, 95 % CI -0·05, 0·63 mmol/l, P = 0·092), but had no significant effect on total cholesterol:HDL-cholesterol ratio (0·75, 95 % CI - 0·24 to 1·74 mmol/l, P = 0·118). No significant difference was observed in fasting as well as 2-h postprandial plasma TAG, glucose, insulin and plasminogen activator inhibitor-1 concentrations. This study showed that ghee that is predominantly saturated fats had an increasing effect on plasma apo B and non-HDL-cholesterol compared with olive oil, adding further evidence to the existing recommendations to replace dietary fats high in SFA with dietary fats high in unsaturated fats to reduce CVD risk.

Postprandial Fatty Acid Profile, but Not Cardiometabolic Risk Markers, Is Modulated by Dairy Fat Manipulation in Adults with Moderate Cardiovascular Disease Risk: The Randomized Controlled REplacement of SaturatEd fat in dairy on Total cholesterol (RESET) Study

BACKGROUND

Chronic consumption of dairy products with an SFA-reduced, MUFA-enriched content was shown to impact favorably on brachial artery flow-mediated dilatation (FMD). However, their acute effect on postprandial cardiometabolic risk biomarkers requires investigation.

OBJECTIVE

The effects of sequential high-fat mixed meals rich in fatty acid (FA)-modified or conventional (control) dairy products on postprandial FMD (primary outcome) and systemic cardiometabolic biomarkers in adults with moderate cardiovascular risk (≥50% above the population mean) were compared.

METHODS

In a randomized crossover trial, 52 participants [mean ± SEM age: 53 ± 2 y; BMI (kg/m2) 25.9 ± 0.5] consumed a high-dairy-fat breakfast (0 min; ∼50 g total fat: modified: 25 g SFAs, 20 g MUFAs; control: 32 g SFAs, 12 g MUFAs) and lunch (330 min; ∼30 g total fat; modified: 15 g SFAs, 12 g MUFAs; control: 19 g SFAs, 7 g MUFAs). Blood samples were obtained before and until 480 min after breakfast, with FMD assessed at 0, 180, 300, and 420 min. Data were analyzed by linear mixed models.

RESULTS

Postprandial changes in cardiometabolic biomarkers were comparable between the different dairy meals, with the exception of a tendency for a 4% higher AUC for the %FMD response following the modified-dairy-fat meals (P = 0.075). Plasma total lipid FA analysis revealed that incremental AUC responses were 53% lower for total SFAs, 214% and 258% higher for total cis-MUFAs (predominantly cis-9 18:1), and trans-18:1, respectively, following the modified relative to the control dairy meals (all P < 0.0001).

CONCLUSIONS

In adults at moderate cardiovascular risk, acute consumption of sequential high-fat meals containing FA-modified dairy products had little impact on postprandial endothelial function or systemic cardiometabolic biomarkers, but a differential effect on the plasma total lipid FA profile, relative to conventional dairy fat meals.This trial was registered at clinicaltrials.gov as NCT02089035.

Effect of Nutrient and Micronutrient Intake on Chylomicron Production and Postprandial Lipemia

Postprandial lipemia, which is one of the main characteristics of the atherogenic dyslipidemia with fasting plasma hypertriglyceridemia, low high-density lipoprotein cholesterol and an increase of small and dense low-density lipoproteins is now considered a causal risk factor for atherosclerotic cardiovascular disease and all-cause mortality. Postprandial lipemia, which is mainly related to the increase in chylomicron production, is frequently elevated in individuals at high cardiovascular risk such as obese or overweight patients, type 2 diabetic patients and subjects with a metabolic syndrome who share an insulin resistant state. It is now well known that chylomicron production and thus postprandial lipemia is highly regulated by many factors such as endogenous factors: circulating factors such as hormones or free fatty acids, genetic variants, circadian rhythms, or exogenous factors: food components, dietary supplements and prescription drugs. In this review, we focused on the effect of nutrients, micronutrients and phytochemicals but also on food structure on chylomicron production and postprandial lipemia.

Postprandial Metabolomics Response to Various Cooking Oils in Humans

Lipids account for a high proportion of dietary calories, which greatly affect human health. As a result of differences in composition of fatty acid of individual cooking oils, certain biological effects of these oils may vary. This study aimed to compare postprandial metabolomic profiles of six commonly consumed cooking oils/fats. Adopting a switch-over experimental design ( n = 15), we carried out a human feeding study with six groups (control without oils, soybean oil, olive oil, palm oil, camellia oil, and tallow) and collected fasting and postprandial serum samples. The metabolomic profile was measured by ultra-high-pressure liquid chromatography-quadrupole time of flight. We observed significant differences between the control group and experimental groups for 33 serum metabolites (false discovery rate; p < 0.05), which take part in lipid digestion, fatty acid metabolism, metabolism of pyrimidines and pyrimidine nucleosides, amino acid metabolism, neurobiology, and antioxidation. Sparse partial least squares discriminant analysis revealed distinct metabolomics patterns between monounsaturated fatty acid (MUFA) and saturated fatty acid oils, between soybean oil, olive oil, and palm oil, and between two MUFA-rich oils (olive and camellia oils). The present metabolomics study suggests shared and distinct metabolisms of various cooking oils/fats.

Clinical Outcomes of Dietary Replacement of Saturated Fatty Acids with Unsaturated Fat Sources in Adults with Overweight and Obesity: A Systematic Review and Meta-Analysis of Randomized Control Trials

BACKGROUND

Obesity and dyslipidemia are frequently treated with dietary interventions before pharmacotherapy is given. Diets high in unsaturated fat have proven advantageous to disease treatment.

AIMS

The purpose of this systematic review and meta-analysis was to assess the evidence of the effect of saturated fatty acids (SFA) replacement with unsaturated fatty acids (UFA) in metabolically healthy adults with overweight and obesity on markers of dyslipidemia and body composition.

METHODS

Keyword search was performed in PubMed, CINAHL, and Cochrane Library for randomized controlled trials (RCTs) evaluating the effects of fatty acid substitution in adults with overweight and obesity. Meta-analysis was performed on interventions assessing lipoprotein levels and body composition. Publication bias was assessed by funnel plot inspection, Begg's, and Egger's test.

RESULTS

Eight RCTs enrolling 663 participants were included in the review, with intervention durations between 4 and 28 weeks. Although nonsignificant (p = 0.06), meta-analysis found UFA replacement to reduce total cholesterol concentrations by 10.68 mg/dL (95%CI -21.90 to 0.53). Reductions in low-density lipoprotein cholesterol and triglycerides were statistically nonsignificant.

CONCLUSIONS

Due to null results and a small number of studies included, there is no strong evidence that replacement of SFA with UFA may benefit lipid profiles in this population.

Link of dietary patterns with metabolic syndrome: analysis of the National Health and Nutrition Examination Survey

BACKGROUND

Population-based interventions aimed at halting the increasing prevalence of metabolic syndrome (MetS) require thorough understanding of dietary interplays. Objective is to identify the independent dietary nutrients associated with MetS and its components using dietary pattern identification and the single-nutrient approaches in The United States.

METHODS

This is a cross-sectional observation. Participants are selected from the National Health and Nutrition Examination Survey (NHANES) with available dietary intake, biochemical and anthropometrical data from 2001 to 2012. Exposure is diet obtained from 24-h dietary recall. Main outcome measure is MetS and its components.

RESULTS

Overall, 23 157 eligible individuals including 6561 with MetS were included in the final analysis. Using principle component analysis, we identified three food patterns that explained 50.8% of the variance of the dietary nutrient consumption. The highest quartile of the factor score representative of saturated/monounsaturated fatty acids or the first dietary pattern was associated with 1.27-fold (95% confidence interval (CI): 1.10-1.46, P=0.001) higher odds of association with MetS when compared with the first quartile. The second pattern representative of vitamins and trace elements had an odds ratio of 0.79 (95% CI: 0.70-0.89, P<0.001) for association with MetS, and the third pattern representative of polyunsaturated fatty acids did not have any association with MetS. The nutrient-by-nutrient approach showed that mild alcohol intake and lower consumption of total saturated fatty acids and sodium were associated with lower risk of MetS.

CONCLUSIONS

Application of multiple complementary analytic approaches reveals more comprehensive dietary determinants of MetS and its components as potential intervening targets.

New Insights into the Regulation of Chylomicron Production

Dietary lipids are efficiently absorbed by the small intestine, incorporated into triglyceride-rich lipoproteins (chylomicrons), and transported in the circulation to various tissues. Intestinal lipid absorption and mobilization and chylomicron synthesis and secretion are highly regulated processes. Elevated chylomicron production rate contributes to the dyslipidemia seen in common metabolic disorders such as insulin-resistant states and type 2 diabetes and likely increases the risk for atherosclerosis seen in these conditions. An in-depth understanding of the regulation of chylomicron production may provide leads for the development of drugs that could be of therapeutic utility in the prevention of dyslipidemia and atherosclerosis. Chylomicron secretion is subject to regulation by various factors, including diet, body weight, genetic variants, hormones, nutraceuticals, medications, and emerging interventions such as bariatric surgical procedures. In this review we discuss the regulation of chylomicron production, mechanisms that underlie chylomicron dysregulation, and potential avenues for future research.

Role of the gut in modulating lipoprotein metabolism

The intestinal production of lipoproteins is one of the key processes by which the body prepares dietary lipid for dissemination to locations throughout the body where they are required. Paramount to this is the relationship between dietary lipid and the enterocytes that line the gut, along with the processes which prepare this lipid for efficient uptake by these cells. These include those which occur in the mouth and stomach along with those which occur within the intestinal lumen itself. Additionally, the interplay between digested lipid, dual avenues for lipid uptake by enterocytes (passive and lipid transporter proteins), a system of intercellular lipid resynthesis and transport, and a complex system of lipoprotein synthesis yield a system open to significant modulation. In this review, we will attempt to outline the processes of lipid digestion, lipoprotein synthesis and the exogenous and endogenous factors which exert their influence.

Apolipoprotein E genotype has a modest impact on the postprandial plasma response to meals of varying fat composition in healthy men in a randomized controlled trial

BACKGROUND

Apolioprotein E (APOE) genotype is reported to influence a person's fasting lipid profile and potentially the response to dietary fat manipulation. The impact of APOE genotype on the responsiveness to meals of varying fat composition is unknown.

OBJECTIVE

We examined the effect of meals containing 50 g of fat rich in saturated fatty acids (SFAs), unsaturated fatty acids (UNSATs), or SFAs with fish oil (SFA-FO) on postprandial lipemia.

METHOD

A randomized, controlled, test meal study was performed in men recruited according to the APOE genotype (n = 10 APOE3/3, n = 11 APOE3/E4).

RESULTS

For the serum apoE response (meal × genotype interaction P = 0.038), concentrations were on average 8% lower after the UNSAT than the SFA-FO meal in APOE4 carriers (P = 0.015) only. In the genotype groups combined, there was a delay in the time to reach maximum triacylglycerol (TG) concentration (mean ± SEM: 313 ± 25 vs. 266 ± 27 min) and higher maximum nonesterified fatty acid (0.73 ± 0.05 vs. 0.60 ± 0.03 mmol/L) and glucose (7.92 ± 0.22 vs. 7.25 ± 0.22 mmol/L) concentrations after the SFA than the UNSAT meal, respectively (P ≤ 0.05). In the Svedberg flotation rate 60-400 TG-rich lipoprotein fraction, meal × genotype interactions were observed for incremental area under the curve (IAUC) for the TG (P = 0.038) and apoE (P = 0.016) responses with a 58% lower apoE IAUC after the UNSAT than the SFA meal (P = 0.017) in the E4 carriers.

CONCLUSIONS

Our data indicate that APOE genotype had a modest impact on the postprandial response to meals of varying fat composition in normolipidemic men. The physiologic importance of greater apoE concentrations after the SFA-rich meals in APOE4 carriers may reflect an impact on TG-rich lipoprotein clearance from the circulation. This trial was registered at clinicaltrials.gov as NCT01522482.

Peripheral arterial disease, type 2 diabetes and postprandial lipidaemia: Is there a link?

Peripheral arterial disease, manifested as intermittent claudication or critical ischaemia, or identified by an ankle/brachial index < 0.9, is present in at least one in every four patients with type 2 diabetes mellitus. Several reasons exist for peripheral arterial disease in diabetes. In addition to hyperglycaemia, smoking and hypertension, the dyslipidaemia that accompanies type 2 diabetes and is characterised by increased triglyceride levels and reduced high-density lipoprotein cholesterol concentrations also seems to contribute to this association. Recent years have witnessed an increased interest in postprandial lipidaemia, as a result of various prospective studies showing that non-fasting triglycerides predict the onset of arteriosclerotic cardiovascular disease better than fasting measurements do. Additionally, the use of certain specific postprandial particle markers, such as apolipoprotein B-48, makes it easier and more simple to approach the postprandial phenomenon. Despite this, only a few studies have evaluated the role of postprandial triglycerides in the development of peripheral arterial disease and type 2 diabetes. The purpose of this review is to examine the epidemiology and risk factors of peripheral arterial disease in type 2 diabetes, focusing on the role of postprandial triglycerides and particles.

Responses to high-fat challenges varying in fat type in subjects with different metabolic risk phenotypes: a randomized trial

Background

The ability of subjects to respond to nutritional challenges can reflect the flexibility of their biological system. Nutritional challenge tests could be used as an indicator of health status but more knowledge on metabolic and immune responses of different subjects to nutritional challenges is needed. The aim of this study was to compare the responses to high-fat challenges varying in fat type in subjects with different metabolic risk phenotypes.

Methodology/Principal Findings

In a cross-over design 42 men (age 50–70 y) consumed three high-fat shakes containing saturated fat (SFA), monounsaturated fat (MUFA) or n-3 polyunsaturated (PUFA). Men were selected on BMI and health status (lean, obese or obese diabetic) and phenotyped with MRI for adipose tissue distribution. Before and 2 and 4 h after shake consumption blood was drawn for measurement of expression of metabolic and inflammation-related genes in peripheral blood mononuclear cells (PBMCs), plasma triglycerides (TAG), glucose, insulin, cytokines and ex vivo PBMC immune response capacity. The MUFA and n-3 PUFA challenge, compared to the SFA challenge, induced higher changes in expression of inflammation genes MCP1 and IL1β in PBMCs. Obese and obese diabetic subjects had different PBMC gene expression and metabolic responses to high-fat challenges compared to lean subjects. The MUFA challenge induced the most pronounced TAG response, mainly in obese and obese diabetic subjects.

Conclusion/Significance

The PBMC gene expression response and metabolic response to high-fat challenges were affected by fat type and metabolic risk phenotype. Based on our results we suggest using a MUFA challenge to reveal differences in response capacity of subjects.

Trial Registration

ClinicalTrials.gov NCT00977262

Beneficial effects of combined olive oil ingestion and acute exercise on postprandial TAG concentrations in healthy young women

Foods high in monounsaturated fat, such as olive oil, and endurance exercise are both known to independently reduce postprandial TAG concentrations. We examined the combined effects of exercise and dietary fat composition on postprandial TAG concentrations in nine healthy pre-menopausal females (age 26·8 (sd 3·3) years, BMI 22·3 (sd 2·0) kg/m2). Each participant completed four, 2 d trials in a randomised order: (1) butter-no exercise, (2) olive oil-no exercise, (3) butter-exercise, (4) olive oil-exercise. On day 1 of the exercise trials, participants walked or ran on a treadmill for 60 min. On the no-exercise trials, participants rested on day 1. On day 2 of each trial, participants rested and consumed an olive oil meal (saturated fat 15 % and unsaturated fat 85 %) or a butter meal (saturated fat 71 % and unsaturated fat 29 %) for breakfast. Venous blood samples were obtained in the fasted state and for 6 h postprandially on day 2. A significant main effect on physical activity (exercise or control) was obtained for plasma TAG concentration (three-way ANOVA, P = 0·043), and the total area under the concentration v. time curve for TAG was 26 % lower on the olive oil-exercise trial (4·40 (sd 0·40) mmol × 6 h/l) than the butter-no exercise trial (5·91 (sd 1·01) mmol × 6 h/l) (one-way ANOVA, P = 0·029). These findings suggest that the combination of exercise and a preference for monounsaturated dietary fat intake in the form of olive oil may be most beneficial for reducing postprandial TAG concentrations.

Palmitic acid in the sn-2 position of triacylglycerols acutely influences postprandial lipid metabolism

BACKGROUND

The triacylglycerol structure of saturated fats may influence postprandial lipemia.

OBJECTIVE

We tested the hypothesis that high-fat meals rich in palmitic acid (16:0) in the sn-2 position decrease lipemia.

DESIGN

Postprandial changes in plasma lipids, apolipoprotein B48, and cytokines were compared in healthy men (n = 25) and women (n = 25) by using a randomized crossover design after meals that provided 50 g fat supplied as high-oleic sunflower oil (control), palm olein (PO), interesterified palm olein (IPO), and lard containing 0.6, 9.2, 39.1, and 70.5 mol% 16:0, respectively, at sn-2.

RESULTS

The sn-2-rich meals elicited different postprandial responses in plasma concentrations of nonesterified fatty acid (meal × time, P = 0.00014), triacylglycerol (meal × time, P = 0.002), and apolipoprotein B48 (meal × time × sex, P = 0.008). Nonesterified fatty acid concentrations were lower up to 3 h after lard and IPO meals than after control or PO meals. Triacylglycerol increased less steeply after lard and IPO meals than after control and PO meals; the incremental AUCs (iAUCs) were 34% (95% CI: 7%, 124%; P < 0.05) and 26% (95% CI: 16%, 132%; P < 0.05) lower after lard than after control and PO meals, respectively. In men, the maximal increment in apolipoprotein B48 was 14% (95% CI: 3%, 25%; P < 0.05) and 16% (95% CI: 2%, 30%; P < 0.05) lower for lard and IPO, respectively, compared with control. The postprandial iAUC in triacylglycerol was 51% lower in women (P = 0.001) than in men. Plasma IL-6 increased postprandially, but IL-8, TNF-α, and E-selectin decreased after all meals.

CONCLUSION

Fats with a higher proportion of palmitic acid in the sn-2 position decrease postprandial lipemia in healthy subjects. This trial was registered at controlled-trials.com as ISRCTN20774126.

Physical activity and postprandial lipidemia: are energy expenditure and lipoprotein lipase activity the real modulators of the positive effect?

Historically, the link between elevated cholesterol and increased risk of cardiovascular disease has been based on fasting measurements. This is appropriate for total, low-density lipoprotein and high-density lipoprotein cholesterol. However, triglyceride concentrations vary considerably throughout the day in response to the regular consumption of food and drink. Recent findings indicate that postprandial triglyceride concentrations independently predict future cardiovascular risk. Potential modulators of postprandial lipidemia include meal composition and physical activity. Early cross sectional studies indicated that physically active individuals had a lower postprandial lipidemic response compared to inactive individuals. However, the effect of physical activity on postprandial lipidemia is an acute phenomenon, which dissipates within 60 h of a single bout of exercise. Total exercise induced energy expenditure, rather than duration or intensity of the physical activity is commonly reported to be a potent modulator of postprandial lipidemia. However, the pooled results of studies in this area suggest that energy expenditure exerts most of its influence on fasting triglyceride concentrations rather than on the incremental change in triglyceride concentrations seen following meal consumption. It seems more likely that energy expenditure is one component of a multifactorial list of mediators that may include local muscle contractile activity, and other yet to be elucidated mechanisms.

Introduction to the DISRUPT postprandial database: subjects, studies and methodologies

Dysregulation of lipid and glucose metabolism in the postprandial state are recognised as important risk factors for the development of cardiovascular disease and type 2 diabetes. Our objective was to create a comprehensive, standardised database of postprandial studies to provide insights into the physiological factors that influence postprandial lipid and glucose responses. Data were collated from subjects (n = 467) taking part in single and sequential meal postprandial studies conducted by researchers at the University of Reading, to form the DISRUPT (DIetary Studies: Reading Unilever Postprandial Trials) database. Subject attributes including age, gender, genotype, menopausal status, body mass index, blood pressure and a fasting biochemical profile, together with postprandial measurements of triacylglycerol (TAG), non-esterified fatty acids, glucose, insulin and TAG-rich lipoprotein composition are recorded. A particular strength of the studies is the frequency of blood sampling, with on average 10-13 blood samples taken during each postprandial assessment, and the fact that identical test meal protocols were used in a number of studies, allowing pooling of data to increase statistical power. The DISRUPT database is the most comprehensive postprandial metabolism database that exists worldwide and preliminary analysis of the pooled sequential meal postprandial dataset has revealed both confirmatory and novel observations with respect to the impact of gender and age on the postprandial TAG response. Further analysis of the dataset using conventional statistical techniques along with integrated mathematical models and clustering analysis will provide a unique opportunity to greatly expand current knowledge of the aetiology of inter-individual variability in postprandial lipid and glucose responses.

Macronutrient intake and modulation on chylomicron production and clearance

The extent and kinetics of postprandial changes are highly variable and are modulated by numerous factors including diet, lifestyle conditions, genetic background and pathological conditions. This review focuses on dietary factors affecting postprandial chylomicron and lipoprotein metabolism in humans. The first key step in the process is fat digestion within the stomach and small intestine which can be modulated by fat and dietary fiber amounts and types. The second key step is intestinal absorption per se. The uptake and secretion of absorbed nutrients in chylomicrons is affected by numerous factors, including nutrients themselves. The amount of dietary triglycerides as well as the nature of fatty acids ingested from habitual diet or present in a test meal modulates the extent of chylomicron and plasma triglyceride levels postprandially. The amount of dietary cholesterol also modulates the extent of postprandial chylomicron and plasma triglycerides. Other nutrients can alter the postprandial occurrence of chylomicrons such as proteins, alcohol, carbohydrates or fibers. Addition of glucose and more markedly fructose, to a fat test meal increases the accumulation of chylomicrons, as does a high-glycemic index meal. In contrast, some sources of dietary fibers such as oat bran noticeably decrease the occurrence of chylomicron postprandially. Overall, changing the habitual dietary pattern, for instance from a Western-type diet to Mediterranean-type one, can in turn alter the postprandial response of the subjects. The last step in postprandial lipid metabolism is clearance from plasma through combined lipolysis processes and tissue uptake of chylomicron remnants. Both the processes can also be modulated by the nutrients. Because most day-time is usually spent in a postprandial state, the link between dietary patterns and cardiovascular health or risk is clearly mediated by the secretion and clearance rates of chylomicrons in the circulation.

Lipid, glycemic, and insulin responses to meals rich in saturated, cis-monounsaturated, and polyunsaturated (n-3 and n-6) fatty acids in subjects with type 2 diabetes

OBJECTIVE

The recommendations for dietary fats in patients with type 2 diabetes are based largely on the impact of fatty acids on fasting serum lipid and glucose concentrations. How fatty acids affect postprandial insulin, glucose, and triglyceride concentrations, however, remains unclear. The objective of this study was to study the effect of fatty acids on postprandial insulin, glucose, and triglyceride responses.

RESEARCH DESIGN AND METHODS

Test meals rich in palmitic acid, linoleic acid, oleic acid, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and containing 1,000 kcal each were administered in a randomized crossover design to 11 type 2 diabetic subjects. Serum insulin, glucose, and triglyceride concentrations were measured for 360 min. All subjects received an isoenergetic diet of constant composition throughout the study.

RESULTS

According to repeated-measures ANOVA, the insulin (P = 0.0002) but not glucose (P = 0.10) response was significantly different between meals. The insulin response was lower to meals rich in oleic acid or EPA and DHA than to meals rich in palmitic acid or linoleic acid (P < 0.01). The triglyceride response did not reach statistical significance (P = 0.06) but tended to be lower with EPA and DHA than with the other fatty acids. Similar trends were seen for area under the curve (AUC) and incremental AUC for serum insulin and triglycerides, but the differences were not significant.

CONCLUSIONS

In comparison with palmitic acid and linoleic acid, oleic acid or EPA and DHA may modestly lower insulin response in patients with type 2 diabetes without deteriorating the glucose response. EPA and DHA may also reduce the triglyceride response.

Dietary, physiological, genetic and pathological influences on postprandial lipid metabolism

Most of diurnal time is spent in a postprandial state due to successive meal intakes during the day. As long as the meals contain enough fat, a transient increase in triacylglycerolaemia and a change in lipoprotein pattern occurs. The extent and kinetics of such postprandial changes are highly variable and are modulated by numerous factors. This review focuses on factors affecting postprandial lipoprotein metabolism and genes, their variability and their relationship with intermediate phenotypes and risk of CHD. Postprandial lipoprotein metabolism is modulated by background dietary pattern as well as meal composition (fat amount and type, carbohydrate, protein, fibre, alcohol) and several lifestyle conditions (physical activity, tobacco use), physiological factors (age, gender, menopausal status) and pathological conditions (obesity, insulin resistance, diabetes mellitus). The roles of many genes have been explored in order to establish the possible implications of their variability in lipid metabolism and CHD risk. The postprandial lipid response has been shown to be modified by polymorphisms within the genes for apo A-I, A-IV, A-V, E, B, C-I and C-III, lipoprotein lipase, hepatic lipase, fatty acid binding and transport proteins, microsomal triglyceride transfer protein and scavenger receptor class B type I. Overall, the variability in postprandial response is important and complex, and the interactions between nutrients or dietary or meal compositions and gene variants need further investigation. The extent of present knowledge and needs for future studies are discussed in light of ongoing developments in nutrigenetics.

Methodology for studying postprandial lipid metabolism

BACKGROUND

Postprandial lipid metabolism in humans has deserved much attention during the last two decades. Although fasting lipid and lipoprotein parameters reflect body homeostasis to some extent, the transient lipid and lipoprotein accumulation that occurs in the circulation after a fat-containing meal highlights the individual capacity to handle an acute fat input. An exacerbated postprandial accumulation of triglyceride-rich lipoproteins in the circulation has been associated with an increased cardiovascular risk.

METHODS

The important number of studies published in this field raises the question of the methodology used for such postprandial studies, as reviewed.

RESULTS

Based on our experiences, the present review reports and discuss the numerous methodological issues involved to serve as a basis for further works. These aspects include aims of the postprandial tests, size and nutrient composition of the test meals and background diets, pre-test conditions, characteristics of subjects involved, timing of sampling, suitable markers of postprandial lipid metabolism and calculations.

CONCLUSION

In conclusion, we stress the need for standardization of postprandial tests.

The effect of acute carbohydrate load on the monophasic or biphasic nature of the postprandial lipaemic response to acute fat ingestion in human subjects

Previous studies in this laboratory have elicited a monophasic response in postprandial plasma triacylglycerol (TAG) level with fat intakes of 0.5 g fat/kg body weight accompanied by about 17 g carbohydrate as lactose. Recent studies involving the same level of fat with a higher level of carbohydrate, 136 g of which 60 g was sucrose, appeared to elicit a biphasic response. The present study compared these two test meals and showed a significant meal × time interaction for plasma total TAG (P = 0.0228) reflecting a monophasic response with the lower-carbohydrate test meal. The higher-carbohydrate meal induced significantly higher insulin and glucose-dependent insulinotropic polypeptide responses (P = 0.0009 and P = 0.0041 respectively). A significant meal × time interaction was seen for plasma non-esterified fatty acids (P = 0.0437). The biphasic plasma TAG response seen with the high-carbohydrate meal largely reflected the TAG-rich lipoprotein (TRL) or chylomicron fraction, which would tend to suggest a biphasic pattern of absorption. This was borne out by TRL-TAG fatty acid compositions. Both peaks in the biphasic response showed active incorporation of the main dietary fatty acids, 18:1n−9, 18:2n−6 and 18:3n−3 into TRL-TAG. These results indicate that under the specific test-meal conditions used in the present study, a biphasic pattern of fat absorption was seen.

The effect of low and moderate fat intakes on the postprandial lipaemic and hormonal responses in healthy volunteers

Present literature indicates that whereas an acute fat intake of 5 g does not elicit a postprandial triacylglycerolaemic response, 20 g of fat does. Since 67 % of fat intake occasions involve fat doses of less than 20 g, the present study examined the effect of a relatively low-fat (LF) meal (0·2 g/kg body weight; mean 14 g) on postprandial triacylglycerol (TAG) metabolism, compared with a high-fat (HF) meal (0·6 g/kg body weight; mean 43 g), a fat dose which is more typical of laboratory studies. Plasma- and chylomicron-TAG concentrations increased significantly (P ≤ 0·001) following both meals, and the increase was significantly (P ≤ 0·02) greater after the HF meal. The postprandial areas under the curves and maximal postprandial TAG concentrations for plasma- and chylomicron-TAG were significantly higher following the HF meal (P ≤ 0·05). Postprandial plasma insulin and gastric inhibitory polypeptide concentrations increased significantly (P ≤ 0·001) after each meal, but there was no difference between the two meals. These data show that modest amounts of fat in a meal will elicit a measurable postprandial TAG response. Since postprandial lipaemia affects the composition and concentration of the TAG- and cholesterol-rich lipoproteins, controlling dietary TAG supply may influence the metabolic fate of these lipoproteins.

Influence of triacylglycerol structure of stearic acid-rich fats on postprandial lipaemia

Exaggerated postprandial lipaemia may increase the risk of CHD by contributing to both thrombotic and atherogenic processes. Previous research has focused on the quantity and composition of dietary fat, whereas the effect of triacylglycerol (TAG) structure on postprandial lipaemia and clotting factor VII activity has received little attention. TAG with similar fatty acid composition may have different biochemical and physical properties that are dependent on their TAG structure, and these differences may affect lipid metabolism. Recent findings suggest that differences in the physical properties of stearic acid-rich fats are associated with differences in postprandial lipaemia, and may play an important role in determining their rates of digestion and absorption.

Acute effects of meal fatty acids on postprandial NEFA, glucose and apo E response: implications for insulin sensitivity and lipoprotein regulation?

Our aim was to determine whether meal fatty acids influence insulin and glucose responses to mixed meals and whether these effects can be explained by variations in postprandial NEFA and Apo, which regulate the metabolism of triacylglycerol-rich lipoproteins (Apo C and E). A single-blind crossover study examined the effects of single meals enriched in saturated fatty acids SFA), n-6 PUFA and MUFA on plasma metabolite and insulin responses. The triacylglycerol response following the PUFA meal showed a lower net incremental area under the curve than following the SFA and MUFA meals (P<0.007). Compared with the SFA meal, the PUFA meal showed a lower net incremental area under the curve for the NEFA response from initial suppression to the end of the postprandial period (180-480 min; P<0.02), and both PUFA and MUFA showed a lower net incremental glucose response (P<0.02), although insulin concentrations were similar between meals. The pattern of the Apo E response was also different following the SFA meal (P<0.02). There was a significant association between the net incremental NEFA (180-480 min) and glucose response (rs=0.409, P=0.025), and in multiple regression analysis the NEFA response accounted for 24 % of the variation in glucose response. Meal SFA have adverse effects on the postprandial glucose response that may be due to greater elevations in NEFA arising from differences in the metabolism of SFA- v. PUFA- and MUFA-rich lipoproteins. Elevated Apo E responses to high-SFA meals may have important implications for the hepatic metabolism of triacylglycerol-rich lipoproteins.

Effect of dietary fatty acids on the postprandial fatty acid composition of triacylglycerol-rich lipoproteins in healthy male subjects

OBJECTIVE

The aim of the present study was to investigate the effect of trans-18:1 isomers compared to other fatty acids, especially saturates, on the postprandial fatty acid composition of triacylglycerols (TAG) in chylomicrons and VLDL.

DESIGN

A randomised crossover experiment where five interesterified test fats with equal amounts of palmitic acid (P fat), stearic acid (S fat), trans-18:1 isomers (T fat), oleic acid (O fat), or linoleic acid (L fat) were tested.

SUBJECTS

A total of 16 healthy, normolipidaemic males (age 23+/-2 y) were recruited.

INTERVENTIONS

The participants ingested fat-rich test meals (1 g fat per kg body weight) and the fatty acid profiles of chylomicron and VLDL TAG were followed for 8 h.

RESULTS

The postprandial fatty acid composition of chylomicron TAG resembled that of the ingested fats. The fatty acids in chylomicron TAG were randomly distributed among the three positions in accordance with the distributions in test fats. Calculations of postprandial TAG concentrations from fatty acid data revealed increasing amounts up to 4 h but lower response curves (IAUC) for the two saturated fats in accordance with previous published data. The T fat gave results comparable to the O and L fats. The test fatty acids were much less reflected in VLDL TAG and there was no dietary influence on the response curves.

CONCLUSIONS

The fatty acid composition in the test fats as well as the positional distributions of these were maintained in the chylomicrons. No specific clearing of chylomicron TAG was observed in relation to time.

Gender influence on plasma triacylglycerol response to meals with different monounsaturated and saturated fatty acid content

OBJECTIVE

Both gender and meal fatty acid composition modulate postprandial triacylglycerol (TAG) metabolism, but little information exists on their interaction. We compared postprandial TAG concentrations in men and women after test meals differing in the proportion of monounsaturated (MUFA) and saturated fatty acids (SFA).

SUBJECTS

Nine men (body mass index, BMI: 24.5+/-2.3 kg/m(2)) (mean+/-s.d.) and 10 premenopausal women (BMI: 21.2+/-1.7 kg/m(2)), young and healthy, habituated to a relatively high MUFA diet.

DESIGN

Plasma responses were studied after subjects consumed two meals, each providing 60 g of fat and 4.7 MJ, on different occasions: one meal was rich in MUFA (MUFA meal: 40 g MUFA; 12 g SFA) and the other meal was rich in SFA (SFA meal: 20 g MUFA; 32 g SFA). The total body and abdominal fat mass were assessed by dual energy X-ray absorptiometry.

RESULTS

Fasting plasma TAG concentration did not differ between meals or genders. No gender differences were observed in either total body or abdominal fat mass. The area under the plasma concentration vs time curve was on average 60% higher (P<0.001) in men than women. Repeated measures ANOVA showed a significant effect of meal x time interaction in men (P<0.001) but not in women (P=0.84). In men, maximal plasma TAG occurred at 4 h and was significantly greater after the MUFA meal (2.10+/-0.20 mmol/l) (mean+/-s.e.m.) than after the SFA meal (1.66+/-0.19 mmol/l) (P=0.01). TAG concentration at 5 h was also significantly greater after the MUFA meal. In women, the patterns of TAG responses were identical after the MUFA and SFA meals.

CONCLUSIONS

This study provides evidence that gender influences postprandial TAG concentrations when meal fatty acid composition is altered.

Effect of moderate changes in dietary fatty acid profile on postprandial lipaemia, haemostatic and related CVD risk factors in healthy men

OBJECTIVE

To investigate the effect of moderate changes in dietary fatty acid profile on postprandial risk factors for cardiovascular disease (CVD).

DESIGN

Double-blind, randomised, crossover, intervention trial.

SETTING

: University of Auckland Human Nutrition Unit, New Zealand.

SUBJECTS

A total of 18 lean healthy men.

INTERVENTION

A dairy butter fat modified to reduce the saturated:unsaturated fatty acid ratio and a conventional high saturated butter fat were given on two separate occasions as a high-fat test meal (59+/-4 g fat; 71 en% fat) at breakfast. A fat exclusion lunch, dinner and snacks were also given. Blood samples were collected at 0 (baseline), 1, 3, 6, 10 and 24 h.

RESULTS

Maximum peak in total triacylglycerol (TAG) occurred 3 h postprandially and was highest on modified treatment (diet, P<0.05) due predominantly to increased TAG within the chylomicron-rich fraction. Transient peaks in total-, LDL- and HDL-cholesterol occurred postprandially, but did not differ between dietary treatments (P>0.05). There were no differential effects of diet on postprandial free fatty acids, apo A, apo B, glucose, insulin, amylin or haemostatic clotting factors (P>0.05).

CONCLUSIONS

In a group of healthy young men, replacement of 16% of total saturated fatty acids by mono- and polyunsaturated fats within a dairy lipid did not induce postprandial changes in CVD risk that may be considered beneficial for health.

SPONSORSHIP

Fonterra, Wellington; New Zealand.

Effect of individual dietary fatty acids on postprandial activation of blood coagulation factor VII and fibrinolysis in healthy young men

BACKGROUND

Hypertriglyceridemia may represent a procoagulant state involving disturbances to the hemostatic system. Plasminogen activator inhibitor type 1 (PAI-1) is increased in the presence of hypertriglyceridemia. Free fatty acids (FFAs) in plasma may promote factor VII (FVII) activation.

OBJECTIVE

We tested the hypothesis that FVII activation would be less after consumption of saturated fatty acids than after other fatty acids.

DESIGN

The effects of 6 matching dietary test fats, rich in stearic (S), palmitic (P), palmitic + myristic (M), oleic (O), trans 18:1 (T), and linoleic (L) acid, respectively, on the postprandial lipid and hemostatic profile (after 2, 4, 6, and 8 h) were investigated in 16 young men. High-fat meals (1 g fat/kg body wt; 43% from the test fatty acid) were served in the morning on 6 separate days.

RESULTS

All fats increased FVII activation. The S fat resulted in a lower increase in activated FVII (FVIIa) than did the T fat and in a lower FVII coagulant activity (FVII:c) than did the O fat (P < 0.02, diet x time interaction). When the data were pooled, the saturated (S, P, and M) test fats resulted in a smaller postprandial increase in FVIIa (P = 0.036, diet effect), a smaller increase in FVII:c (P < 0.001, diet x time interaction), a greater rise in tissue plasminogen activator concentrations (P = 0.028, diet effect), and a tendency to a greater postprandial decline in PAI-1 (P = 0.06, diet effect) compared with the unsaturated test fats (O, T, and L). The increase in FVIIa was not significantly associated with the level of lipemia, plasma FFAs, or plasma lipoprotein lipase activity.

CONCLUSION

Our results indicate a lesser increase in FVIIa after the consumption of saturated fats, especially the S fat, than after unsaturated test fats.

Oral fat exposure increases the first phase triacylglycerol concentration due to release of stored lipid in humans

Oral exposure to dietary fat (through modified sham feeding, which entails mastication and expectoration of foods) augments the postprandial triacylglycerol (TAG) concentration, in part, though augmented lipid absorption. This study was designed to characterize early events in this process. At 2200 h, 25 healthy adults (13 men, 12 women) consumed 80 g of almonds (high oleic acid content) and fasted until approximately 0700 h. After placement of a catheter in a hand vein and 4 blood draws at 10-min intervals, 50 1-g safflower oil (high linoleic acid content) capsules were consumed. After another blood draw, modified sham feeding was initiated with a cracker only or cracker with cream cheese in random order with 1 wk between trials. Oral exposures occurred at 5-min intervals for 60 min then at 15-min intervals from min 60 to 120. Additional blood draws occurred at 2, 4, 6, 8, 10, 12, 14, 30, 60, 120, 240, 360 and 480 min. Oral stimulation, especially by fat, prompted the rapid (mean approximately 23 min) release of lipid stored from the previous meal (almonds) in all participants. This resulted in multimodal postprandial triacylglycerol (TAG) peaks generally occurring at 0-30 min, 60-120 min and 240-480 min after loading and initiation of oral stimulation. TAG magnitudes during these times were correlated (r = 0.40-0.89, P < 0.001-P = 0.053). It is proposed that the sensory-enhanced release of lipid from the residual pool initiates an early TAG rise, which augments the peak attributable to absorption of meal lipid; this in turn supplements a later peak associated with release of endogenously synthesized TAG because lipid from all three sources competed for a common clearance mechanism. If substantiated, additional understanding of the behavioral factors (e.g., eating patterns) that initiate this cascade will be warranted.

Acute-on-chronic effects of fatty acids on intestinal triacylglycerol-rich lipoprotein metabolism

Postprandial triacylglycerol (TAG) metabolism is an important metabolic state that has been associated with cardiovascular disease. The magnitude of the postprandial TAG response is determined by dietary fat composition, which alters intestinal and hepatic TAG-rich lipoprotein (TRL) metabolism. Caco-2 cell monolayers are morphologically and physiologically similar to the human intestinal enterocytes, hence they are a good model to study intestinal lipoprotein metabolism. To date only the acute effect of fatty acid composition on intestinal TRL metabolism in Caco-2 cells has been investigated. Little is known of the effect of habitual, or chronic, dietary fat composition on intestinal TRL metabolism. Using the Caco-2 cell model, the present study investigated the acute-on-chronic effect of fatty acid composition on TRL metabolism. Caco-2 cells were grown in the presence of 0.05 mm-palmitic acid (PA; 16 : 0), -oleic acid (OA; 18 : 1n-9),-eicosapentaenoic acid (EPA; 20 : 5n-3) or no fatty acid (control) for 19 d, then one of four acute treatments (control (bovine serum albumin (BSA; 5 g/l)) or BSA (5 g/l) plus 0.5 mm-PA, -OA or -EPA) were administered for 22 h. Significant acutexchronic interactions for the effect of fatty acid composition on cellular TAG:secreted de novo TAG, and cellular de novo TAG:de novo phospholipid were observed. Thus the effect of a fatty acid was determined by the duration of exposure to the fatty acid intervention. Acute PA treatment increased de novo TAG synthesis, but chronic PA supplementation did not. Acute and chronic OA treatments increased de novo TAG secretion. For EPA, chronic supplementation had the greatest effect on TAG synthesis and secretion. The acute-on-chronic effects of fatty acids on apolipoprotein B metabolism were relatively minor compared with the changes noted for TRL lipid composition. The present study shows that the Caco-2 cell model is valuable for studying intestinal TRL metabolism and that fatty acids modulate this process, the nature of which can be determined by the length of exposure of the cell to the fatty acid.

Butter differs from olive oil and sunflower oil in its effects on postprandial lipemia and triacylglycerol-rich lipoproteins after single mixed meals in healthy young men

Accumulation of postprandial triacylglycerol-rich lipoproteins is generated by assimilation of ingested dietary fat and has been increasingly related to atherogenic risk. Nevertheless, the influence of different kinds of dietary fatty acids on postprandial lipid metabolism is not well established, except for (n-3) polyunsaturated long-chain fatty acids. Our goal was to evaluate the effects of test meals containing a common edible fat source of saturated (butter), monounsaturated (olive oil) or (n-6) polyunsaturated (sunflower oil) fatty acids on postprandial lipid and triacylglycerol-rich lipoprotein responses. After a 12-h fast, 10 healthy young men ingested mixed meals containing 0 g (control) or 40 g fat, provided as butter, olive oil or sunflower oil in a random order. Fasting and postmeal blood samples were collected for 7 h. The no-fat test meal did not elicit any change over baseline except for plasma phospholipids, insulin and nonesterified fatty acids. Conversely, the three fat-containing meals elicited bell-shaped postprandial changes (P < 0.05) in serum triacylglycerols, free and esterified cholesterol, and nonesterified fatty acids. The butter meal induced a lower postprandial rise of triacylglycerols in serum and chylomicrons (incremental AUC, mmol.h/L: 0.72) than the two unsaturated oils (olive oil: 1.6, sunflower oil: 1.8), which did not differ. Circulating chylomicrons were smaller after the butter meal than after the two vegetable oil meals. The in vitro susceptibility of circulating chylomicrons to hydrolysis by postheparin plasma was higher after sunflower oil than after butter or olive oil. We conclude that butter results in lower postprandial lipemia and chylomicron accumulation in the circulation of young men than olive or sunflower oils after consumption of a single mixed meal.

Triacylglycerol-rich lipoproteins trigger the phosphorylation of extracellular-signal regulated kinases in vascular cells

Postprandial triacylglycerol-rich lipoproteins (TRL) have been implicated in the pathophysiology of atherosclerosis, but the intracellular processes by which TRL could affect vascular function are still unknown. Incubation of TRL obtained at 2 h postprandial period with vascular smooth muscle cells (VSMC) produced a tyrosine phosphorylation of the extracellular signal-regulated kinases 1 and 2 (ERK1 and ERK2) that belong to the mitogen-activated protein kinase (MAPK) family. The activation of ERK1 and ERK2 had a maximum at 15 min, returned to baseline by 60 min, and was partially depleted after incubation of cells with a MAPKK inhibitor (PD 098059). In addition, postprandial TRL did competent VSMC for DNA replication through a MAPK pathway. These effects were dependent of the lipid composition of TRL. Our observations suggest that postprandial TRL can trigger activation of the MAPK pathway and induce a mitogenic response in VSMC in a lipid-dependent fashion.

Postprandial and short-term effects of dietary virgin olive oil on oxidant/antioxidant status

It is generally believed that virgin olive oil consumption has beneficial effects, but little is known about its effects postprandially on oxidant/antioxidant status. The aim of this study was to determine changes in oxidative stress biomarkers and lipid profile after a single dose of virgin olive oil and after 1 wk of daily consumption. Sixteen subjects (9 men, 7 women) ingested 50 mL of virgin olive oil in a single dose. Blood samples were collected from 0 to 24 h. Thereafter, 14 participants (8 men, 6 women) followed a 1-wk 25 mg/d virgin olive oil dietary intervention. Blood samples were collected at the end of this period. Serum TAG (P = 0.016), plasma FA (P < 0.001), and lipid peroxidation products in plasma (P< 0.001) and VLDL (P = 0.007) increased, reaching a peak at 4-6 h, and returning to baseline values at 24 h after oil ingestion. The opposite changes were observed in plasma glutathione peroxidase (P = 0.001) and glutathione reductase (GR) (P = 0.042). No changes in LDL lipid peroxidation or resistance to oxidation were observed postprandially. At 24 h, plasma oleic acid remained increased (P < 0.05) and resistance of LDL to oxidation improved (P < 0.05). After 1 wk of virgin olive oil consumption, plasma oleic acid (P = 0.031), resistance of LDL to oxidation (P< 0.05), and plasma GR activity (P = 0.005) increased. These results indicate that changes in oxidant/antioxidant status occur after oral virgin olive oil. Virgin olive oil consumption could provide short-term benefits for LDL resistance to oxidation and in glutathione-related enzyme activities.

Triacylglycerol-rich lipoproteins interact with human vascular cells in a lipid-dependent fashion

Plasma triacylglycerol-rich lipoproteins (TRL) are being considered as a key lipid fraction in the pathogenesis of atherosclerotic cardiovascular disease. Here we compared the influence of two monounsaturated oils [virgin olive oil (VOO) and high-oleic sunflower oil (HOSO)] on the capability of postprandial TRL to interact with two human vascular cell lines [umbilical vein endothelial (HUVEC) and aorta smooth muscle (HASMC) cells]. A fluorescent probe was used for labeling TRL and to determine receptor activity of HUVEC and HASMC. The values for total cell-associated, bound, and internalized TRL were higher in HUVEC, and TRL from VOO was the better ligand recognized but at lower affinity than TRL from HOSO. There was a competitive effect of very low density lipoproteins (VLDL) for the uptake of TRL by cells, which was found to be dependent on the origin/lipid composition of the ligands and cell-type specific. We also conclude that the VLDL receptor (VLDLr) may contribute significantly to the HASMC binding capacity for postprandial TRL mediated by lipoprotein lipase (LPL) or LPL-binding molecules. Our findings are compatible with a selective role of the clustered O-linked sugar domain of the VLDLr in the catabolism of TRL by human vascular cells.

Oral stimulation influences postprandial triacylglycerol concentrations in humans: nutrient specificity

OBJECTIVE

To determined whether the nature of the lipid in an oral stimulus modifies postprandial triacylglycerolemia.

METHODS

Sixteen healthy adults (eight male, eight female) participated in six test sessions conducted weekly. The test sessions were administered randomly after overnight fasts and included: ingestion of 50 grams of butter in capsules (to avoid oral stimulation with lipids) and 500 mL of water in 15 minutes followed by oral stimulation with one of the following foods on a cracker: butter, unsaturated fatty acid (UFA) margarine, jelly, UFA margarine + jelly, cracker alone or no oral stimulation. Sensory stimulation entailed masticating and expectorating approximately 5.0 g samples of each stimulus every three minutes for 110 minutes. Blood was drawn immediately after preload ingestion and at minutes 35, 85, 200, 320, and 440 post loading and analyzed for serum triacylglycerol (TAG), insulin and glucose concentrations.

RESULTS

Only the oral samples containing the UFA margarine led to significant elevations of serum TAG concentration compared to baseline (p < 0.05). Maximum change of TAG concentrations were greater following orosensory stimulation with UFA margarine compared to orosensory stimulation with butter, jelly or UFA margarine + jelly. No differences were observed relative to vehicle alone or no orosensory stimulation, but this is due to lower nadir values for these treatments. Insulin and glucose concentrations were not different between treatments.

CONCLUSION

Oral exposure specifically to an unsaturated dietary lipid augments the postprandial rise of TAG, compared to baseline.

The metabolic availability of dietary triacylglycerols from two high oleic oils during the postprandial period does not depend on the amount of oleic acid ingested by healthy men

Monounsaturated oils, virgin olive oil (VOO) and high oleic sunflower oil (HOSO) are suggested to have selective physiologic effects on humans in the fasting state. The aim of the study was to evaluate whether two oils with equal amounts of oleic acid but with different compositions of minor fatty acids and triacylglycerol molecular species (TAG) could produce different triacylglycerol-rich lipoprotein (TRL)-TAG responses in the postprandial state. Eight normolipidemic men consumed the following three meals in random order on separate occasions with 2 wk between meals: control meal, control meal plus VOO and control meal plus HOSO. Plasma total TAG and TRL-TAG were measured hourly for 7 h after ingestion. TAG and sn-2 positional fatty acids within TAG were analyzed in the TRL fraction. Plasma total TAG concentrations in response to the dietary oils did not differ. However, TRL triglyceridemia was significantly lower after VOO intake (P < 0.05). The molecular species in the TRL fraction returned toward basal levels more quickly (P < 0.05) after VOO than HOSO intake. 2-Positional fatty acid analysis demonstrated higher proportions of stearic and palmitic acids and a lower proportion of oleic acid (P < 0.05) in TRL-TAG derived from HOSO. This study shows that VOO intake results in attenuated postprandial TAG concentration and faster TRL-TAG disappearance from blood compared with HOSO, suggesting that the oleic acid content may not be the main factor affecting TAG metabolism. Minor fatty acids such as linoleic acid and the 2-positional distribution of saturated stearic and palmitic acids into the TAG molecule may be important determinants of postprandial lipemia in normolipidemic men.

Influence of fatty acid chain length and cis/trans isomerization on postprandial lipemia and factor VII in healthy subjects (postprandial lipids and factor VII)

Exaggerated postprandial lipemia is believed to be atherogenic and to influence risk of thrombosis. The postprandial effects on plasma triacylglycerol concentration, factor VII coagulant activity (FVII(c)) and activated FVII concentration (FVII(a)) of five high fat meals (5.2 MJ, 90 g fat) enriched with medium triacylglycerols (MCT, 8:0+10:0), palmitate(16:0), stearate (18:0), elaidate(18:1 trans) and oleate(18:1 cis) were compared with those following a low fat meal (5.2 MJ,10 g fat) in 16 healthy subjects using a randomized crossover design. Postprandial lipemia measured as the area under the curve (AUC arbitrary units) for plasma triacylglycerol concentration (mean+/-SE) was greater following the oleate (5.8+/-1. 05), elaidate (4.3+/-0.79) and palmitate (4.1+/-0.64) meals compared with stearate (2.0+/-0.45) and MCT (1.1+/-0.47) meals. Fatty acid analyses of the chylomicron lipids suggested that approximately one fifth of the dietary stearate was not absorbed. FVII(c) increased following the oleate, elaidate and palmitate meals and fell following the low fat meal; the increase in FVII(c) was correlated with the AUC for plasma TAG (r=0.34; P=0.001). FVII(a) concentration increased following all high fat meals but not following the low fat meal. The increase in FVII(a) at 7 h was greater after the oleate meal than after the stearate and MCT meals. These results do not support the hypothesis that dietary stearate and elaidate are responsible for the postprandial increases in FVII associated with high fat intakes.

Long-chain n-3 polyunsaturated fatty acids and triacylglycerol metabolism in the postprandial state

Elevated plasma triacylglycerol (TG; triglyceride) concentrations, especially in the postprandial state, have been associated with an increased risk of coronary heart disease (CHD). Postprandial lipemia represents a complex series of reactions which occur following the ingestion of a meal containing fat and is associated with a number of adverse metabolic events including the production of atherogenic chylomicron remnants, the formation of the highly atherogenic small dense low density lipoprotein particles, a reduction in the concentration of the cardioprotective high density lipoprotein fraction and the activation of coagulation factor VII. Fish oils are a rich source of the long-chain n-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid and docosahexaenoic acid. Long chain n-3 PUFA are effective hypotriglyceridemic agents, lowering both fasting and postprandial TG concentrations. There is a large body of evidence which shows that n-3 PUFA reduces plasma TG concentrations through reduced endogenous very low density lipoprotein production. This in turn may account for the reduced postprandial lipemic response following n-3 PUFA supplementation. However, this does not preclude a contribution of enhanced chylomicron clearance, which may be mediated through altered chylomicron size, structure or chemical composition, or altered lipoprotein lipase metabolism in terms of enzyme concentration, activity, or affinity for chylomicrons. However the precise biochemical nature of this effect remains to be established. The reduction of postprandial plasma TG concentrations by n-3 PUFA may partly explain why n-3 PUFA intake is inversely related to CHD mortality.

Dietary carbohydrates and triacylglycerol metabolism

There is a growing body of scientific evidence which demonstrates that plasma triacylglycerol (TAG) concentration, especially in the postprandial state, is an important risk factor in relation to the development of CHD. Postprandial hypertriacylglycerolaemia is associated with a number of adverse metabolic risk factors, including the preponderance of small dense LDL, low HDL-cholesterol concentrations and elevated factor VII activity. Traditionally, a low-fat high-carbohydrate diet was used to prevent CHD because it effectively reduces plasma cholesterol concentrations, but this dietary regimen increases plasma TAG concentrations and reduces HDL-cholesterol concentrations. There is substantial epidemiological evidence which demonstrates that high plasma TAG and low plasma HDL concentrations are associated with an increased risk of CHD. Thus, there is reason for concern that the adverse effects of low-fat high-carbohydrate diets on TAG and HDL may counteract or negate the beneficial effect of reducing LDL-cholesterol concentrations. Although there have been no prospective studies to investigate whether reduced fat intake has an adverse effect on CHD, there is strong epidemiological evidence that reducing total fat intake is not protective against CHD. On the other hand, high-fat diets predispose to obesity, and central obesity adversely affects TAG metabolism. There is substantial evidence that in free-living situations low-fat high-carbohydrate diets lead to weight loss, which in turn will correct insulin resistance and plasma TAG metabolism. Clearly there is a need for prospective studies to resolve the issue as to whether low-fat high-carbohydrate diets play an adverse or beneficial role in relation to the development of CHD.

Dietary interventions affecting chylomicron and chylomicron remnant clearance

Interest in effects of diet on postprandial lipoproteins has increased in recent years as a result of accumulating evidence for adverse cardiovascular consequences of elevated concentrations of triglyceride rich lipoproteins. Particular attention has been given to ability of different fatty acids to modulate postprandial lipoprotein responses because of evidence for both harmful and protective cardiovascular properties of the saturated, monounsaturated and omega-6 and omega-3 polyunsaturated fatty acid (PUFA) classes. Evidence for direct atherogenic properties of chylomicron remnants has led to attempts to monitor effects of diet specifically on this lipoprotein class. Limitations in the methods employed to measure chylomicron remnants and the small number of human studies which have evaluated effects of meal, and background diet, fatty acid composition, makes it difficult to draw definitive conclusions at the present time. However consideration of data from both animal and human studies tends to support the conclusion that diets, and meals, rich in PUFA (particularly long chain omega-3 PUFA), result in attenuated postprandial responses of the intestinally-derived lipoproteins. Attenuated responses to high PUFA meals appear to be due to greater rates of clearance and greater activation of lipoprotein lipase (LPL). Attenuated responses to high PUFA background diets may be due to adaptive changes involving both accelerated rates of clearance in peripheral tissues and liver, as well as decreased output of the competitor for chylomicron clearance, very low density lipoprotein (VLDL).