Showing papers by "Duo Li published in 1999"

The effect of diet on plasma homocysteine concentrations in healthy male subjects.

Abstract: Objective: To determine the effect of habitual omnivorous and vegetarian diets on folate and vitamin B12 status and the subsequent effect on homocysteine concentration. Design: Cross-sectional comparison of free-living habitual meat-eaters and habitual vegetarians. Setting: The study was conducted at RMIT University, Melbourne. Subjects: One hundred and thirty-nine healthy male subjects (vegans n=18, ovolacto vegetarians n=43, moderate meat-eaters n=60 and high meat-eaters n=18) aged 20–55 y who were recruited in Melbourne. Outcome measures: Fasting plasma or serum from each subject was analysed for folate, vitamin B12 and homocysteine concentration. A semi-quantitative Food Frequency Questionnaire was completed by a subset of subjects from each group to determine methionine intake. Results: The two meat eating groups consumed significantly greater levels of methionine (P<0.001). There was no clear trend in plasma folate status between groups, however the plasma vitamin B12 concentration decreased progressively from the high-meat-eating group to vegans (P<0.05). An inverse trend was observed with plasma homocysteine concentration, with vegans showing the highest levels and high meat eaters the lowest (P<0.05). Conclusions: Dietary methionine intake has no observable effect on plasma homocysteine concentration. In habitual diets, where folate intake is adequate, lowered vitamin B12 intake from animal foods leads to depleted plasma vitamin B12 concentration with a concomitant increase in homocysteine concentration. The suggested mechanism is the failure to transfer a methyl group from methyl tetrahydrofolate by vitamin B12 in the remethylation of homocysteine to methionine. Sponsorship: The study was funded by the Meat Research Corporation of Australia.

The association of diet and thrombotic risk factors in healthy male vegetarians and meat-eaters.

Abstract: Objective: The aim of this study was to assess thrombosis tendency in subjects who were habitual meat-eaters compared with those who were habitual vegetarians. Design: Cross-sectional comparision of habitual meat-eaters and habitual vegetarians. Setting: Free living subjects. Subjects: One hundred and thirty-nine healthy male subjects (vegans n=18, ovolacto vegetarians n=43, moderate-meat-eaters n=60 and high-meat-eaters n=18) aged 20–55 y who were recruited in Melbourne. Outcome measures: Dietary intake was assessed using a semi-quantitative Food Frequency Questionnaire. The parameters of thrombosis were measured by standard methods. Results: Saturated fat and cholesterol intakes were significantly higher and polyunsaturated fat (PUFA) was significantly lower in the meat-eaters compared with vegetarians. In the meat-eaters, the platelet phospholipids AA levels were significantly higher than in the vegetarians, but there was no increase in ex vivo platelet aggregation and plasma 11-dehydro thromboxane B2 levels. Vegetarians, especially the vegans, had a significantly increased mean collagen and ADP stimulated ex vivo whole blood platelet aggregation compared with meat-eaters. The vegan group had a significantly higher mean platelet volume than the other three dietary groups. However, meat-eaters had a significantly higher cluster of cardiovascular risk factors compared with vegetarians, including increased body mass index, waist to hip ratio, plasma total cholesterol (TC), triacylglycerol and LDL-C levels, ratio of TC/HDL-C and LDL-C/HDL-C and plasma factor VII activity. Conclusions: Consumption of meat is not associated with an increased platelet aggregation compared with vegetarian subjects. Sponsorship: Meat Research Corporation, Australia.

Lipoprotein(a), essential fatty acid status and lipoprotein lipids in female Australian vegetarians.

Abstract: In the present study we investigated serum lipoprotein(a) [Lp(a)] levels, plasma lipids, the serum phospholipid polyunsaturated fatty acid profile and correlates of serum Lp(a) in healthy free-living female vegetarians (n = 50) and omnivores (n = 24) to assess differences which may have implications for cardiovascular risk. Dietary saturated fat and total plasma cholesterol were significantly lower in the vegetarians compared with omnivores. The mean serum Lp(a) concentration was lower in the vegetarians (171 mg/l) than in the omnivores (247 mg/l). The serum Lp(a) concentration was significantly negatively correlated with carbohydrate intake (as % of energy), and positively correlated with plasma total cholesterol. Compared with the omnivores, the vegetarians had significantly lower concentrations of 20:3,n-6, 20:4,n-6, 22:5,n-6, 20:5,n-3, 22:6,n-3 and total n-6 and n-3 polyunsaturated fatty acids, and a lower n-3/n-6 polyunsaturated fatty acid ratio, in serum phospholipids. Lower concentrations of plasma total cholesterol, serum phospholipid total fatty acids, total saturated fatty acids and arachidonic acid, and a tendency towards a lower serum Lp(a) concentration, in vegetarians may have beneficial effects on cardiovascular disease risk. However, the decreased concentration of serum phospholipid n-3 polyunsaturated fatty acids may potentially promote thrombotic risk. Based on the present data, it would seem appropriate for omnivores to reduce their dietary intake of total fat and saturated fat in order to decrease their plasma cholesterol, and vegetarians should perhaps increase their dietary intake of n-3 polyunsaturated fatty acids, and thus improve the balance of n-3/n-6, in order to reduce any thrombotic tendency that might increase their generally low risk of cardiovascular disease.

The metabolism of native and randomized butterfat chylomicrons in the rat is similar.

Abstract: Reportedly’ randomly rearranging the position of fatty acids (FA) in butterfat triacylglycerol (TAG) by interesterification’ thereby lowering the proportion of saturated FA in the sn-2 position’ reduces its hypercholesterolemic and hypertriglyceridemic properties when fed to humans. The aim of this work was to determine if these reductions in plasma cholesterol and TAG could be explained by an improved rate of clearance from the plasma of chylomicrons composed of randomized butterfat’ using a rat model. Acute chylomicron clearance studies demonstrated no differences in fractional clearance rates of cholesteryl esters and TAG from the plasma of rats infused with chylomicrons produced from gastric feeding of either native (NBF) or randomized (RBF) butterfat. Although there was a 14% decrease in the level of saturated FA occupying the sn-2 position of TAG in RBF compared with NBF’ this difference became negligible (∼5%)’ following digestion of the fat and subsequent repackaging of TAG into chylomicrons. These observations suggest that the previously observed reduction in hypercholesterolemic properties of randomized butterfat in rat is unlikely to be explained by improved clearance of chylomicron TAG.

Comparison of n-3 Polyunsaturated Fatty Acids from Vegetable Oils, Meat, and Fish in Raising Platelet Eicosapentaenoic Acid Levels in Humans

Abstract: Results from a recent observation study (1) showed that the n-3/n-6 ratio in plasma and platelet phospholipids (PL) was significantly lower in both ovolacto vegetarian and vegan groups compared with meat-eaters in the study population. Collagenand ADP-stimulated whole blood platelet aggregation showed a significant opposite trend to both plasma and platelet PL n-3/n-6 ratios. Plasma 11 -dehydro thromboxane B 2 (1 l-dehydro TXB2), a stable metabolite of TXA2, was found to be higher in ovolacto vegetarian and vegan groups compared with meat-eaters. That is, these data suggested that the vegetarians had a potentially greater thrombotic risk than the omnivore subjects. The aim of this study was to investigate whether male vegetarian subjects who consumed an increased dietary ratio of o~-linolenic acid (ALA)/linoleic acid exhibit an increased n-3/n-6 polyunsaturated fatty acid (PUFA) ratio in platelet PL, plasma PL, and triacylglycerol (TAG), decreased plasma TX levels, and reduced platetet aggregability compared with their habitual diet. Seventeen healthy male vegetarian subjects aged 22-48 yr were recruited in Melbourne. During the study, all subjects maintained their habitual vegetarian diets, except a proportion of dietary fat was replaced with provided vegetable oils and oil-based margarines. All 17 subjects consumed a low n-3/n-6 ratio diet (safflower oil and safflower oil-based margarine) for 14 d, following which they consumed either a moderate n-3/n-6 ratio diet (canola oil and canola oil-based margarine) or a high n-3/n-6 ratio diet (linseed oil and linseed oilbased margarine) for 28 d. Subjects were requested to refrain from consuming fish during the 42 d of the intervention. Blood samples were collected at day 0 (baseline), day 14, and day 42. Collagen, ADR and arachidonic acid (AA) stimulated whole blood platelet aggregation, plasma hemostatic factors, plasma lipid and lipoprotein lipids, plasma 11-dehydro TXB 2 and ottocopherol, fatty acid composition of platelet and plasma PL, and plasma TAG were measured by standard methods. Significant changes were seen in fatty acid profiles of platelet PL, plasma PL, and plasma TAG. Eicosapentaenoic Lipids 34, $309 (1999). *To whom correspondence should be addressed. Abbreviations: AA, arachidonic acid; ALA, e~-linoleic acid; EPA, eicosapen~ taenoic acid; PL, phospholipids; PUFA, polyunsaturated fatty acid; TAG, triacylglycerol; TX, thromboxane. acid (EPA) and total n-3 PUFA levels, and n-3/n-6 ratio were significantly increased, while the AA/EPA ratio decreased (P < 0.05), following either a canola or a linseed oil-based diet compared with a safflower oil-based diet. Docosapentaenoic acid was significantly increased following linseed oil-based diet compared with the safflower oil-based diet (P < 0.05). There was no significant increase in docosahexaenoic acid in these lipids. No statistically significant differences between the study diet period were observed on the various thrombotic risk factors. We compared these data with a previous study (2) in which 23 adult omnivore subjects consumed 350 g/d of lean red meat for 2 wk (EPA intake = 70 mg/d) or 133 g/d of Atlantic salmon for 2 wk (EPA intake = 847 rag/d) (2). These diets also led to significant changes in platelet EPA levels (0.5 to 0.7% on the red meat diet, P < 0.001, and 0.4 to 1.9% on the salmon diet, P < 0.001, as percentage of total platelet PL). The results indicate that canola and linseed oils have similar effects on the fatty acid profile of platelet PL and plasma lipid. The greatest increases in n-3 PUFA occurred with linseed oil which had the highest ALA content. ALA from the vegetable oils (canola and linseed) used as a dietary fat for daily food preparation had a beneficial effect on alteration of fatty acid profiles of platelet PL and plasma lipids in vegetarian populations. Longer-term studies may be necessary to establish effects of plant source n-3 PUFA on hemostatic function in vegetarians. These data clearly show that dietary EPA alters platelet EPA levels more quickly and more effectively than via endogenous synthesis from dietary ALA. This study demonstrated that 70 mg/d of EPA was more effective than 3.7 g of ALA and almost as effective as 15.4 gtd of ALA in raising platelet EPA levels in short-term studies.