Background: Vegetarians have lower platelet and plasma concentrations of nϪ3 polyunsaturated fatty acids (PUFAs) than do omnivores. We recently showed that male vegetarians have higher platelet aggregability than do omnivores. Objective: We investigated whether male vegetarians (n = 17) who consumed an increased amount of dietary ␣-linolenic acid (ALA) showed any changes in their tissue profile of PUFAs, plasma thromboxane concentrations, platelet aggregability, or hemostatic factors. Design: During the study, all subjects maintained their habitual vegetarian diets except that a proportion of dietary fat was replaced with vegetable oils and margarines that were provided. Initially, all subjects consumed a low-ALA diet (containing safflower oil and safflower oil-based margarine) for 14 d; they then consumed either a moderate-ALA diet (containing canola oil and canola oil-based margarine) or a high-ALA diet (containing linseed oil and linseed oil-based margarine) for 28 d. Blood samples were collected at day 0 (baseline), day 14, and day 42. Results: Eicosapentaenoic acid, docosapentaenoic acid, total nϪ3 PUFAs, and the ratio of nϪ3 to nϪ6 PUFAs were significantly increased (P < 0.05), whereas the ratio of arachidonic acid to eicosapentaenoic acid was decreased (P < 0.05), in platelet phospholipids, plasma phospholipids, and triacylglycerols after either the moderate-ALA or high-ALA diet compared with the low-ALA diet. No significant differences were observed in thrombotic risk factors. Conclusion: ALA from vegetable oils (canola and linseed) has a beneficial effect on nϪ3 PUFA concentrations of platelet phospholipids and plasma lipids in vegetarian males.Am J Clin Nutr 1999;69:872-82. KEY WORDSVegetarian diet, ␣-linolenic acid, linoleic acid, platelet fatty acid, plasma fatty acid, polyunsaturated fatty acids, hemostatic factors, thrombosis, lipoprotein lipids, men INTRODUCTIONThe predominant polyunsaturated fatty acid (PUFA) in the Western diet is linoleic acid (LA; 18:2nϪ6), which is commonly found in vegetable seed oils. LA is the parent fatty acid of the nϪ6 series PUFAs, which can be converted in vivo to 20-and 22-carbon nϪ6 long-chain PUFAs. ␣-Linolenic acid (ALA; 18:3nϪ3) is less abundant than LA; however, it is also present in vegetable oils and is the precursor of 20-and 22-carbon nϪ3 long-chain PUFAs. Omnivores can obtain their 20-and 22-carbon nϪ3 long-chain PUFAs either from dietary ALA or directly by consumption of fish, eggs, or animal products (1). Lactoovovegetarians can gain a limited amount of 20-and 22-carbon nϪ3 long-chain PUFAs from milk, dairy products, and eggs. Because animals can convert ALA to 20-and 22-carbon nϪ3 long-chain PUFAs and plants cannot, there are no 20-or 22-carbon nϪ3 long-chain PUFAs in plant-based vegan diets. Thus, vegans must rely totally on endogenous synthesis from ALA by desaturation and elongation. A diet with a low ratio of nϪ3 to nϪ6 PUFAs (nϪ3:nϪ6) can cause a reduced tissue nϪ3:nϪ6 [ie, increased ratio of arachidonic acid (AA; 20:4nϪ6) to eicosapentaeno...

Objective: To determine whether healthy males who consumed increased amounts of dietary stearic acid compared with increased dietary palmitic acid exhibited any changes in their platelet aggregability, platelet fatty acid pro®les, platelet morphology, or haemostatic factors. Design: A randomized cross-over dietary intervention. Subjects and interventions: Thirteen free-living healthy males consumed two experimental diets for 4 weeks with a 7 week washout between the two dietary periods. The diets consisted of $ 30% of energy as fat (66% of which was the treatment fat) providing $ 6.6% of energy as stearic acid (diet S) or $ 7.8% of energy as palmitic acid (diet P). On days 0 and 28 of each dietary period, blood samples were collected and anthropometric and physiological measurements were recorded. Results: Stearic acid was increased signi®cantly in platelet phospholipids on diet S (by 22%), while on diet P palmitic acid levels in platelet phospholipids also increased signi®cantly (8%). Mean platelet volume, coagulation factor FVII activity and plasma lipid concentrations were signi®cantly decreased on diet S, while platelet aggregation was signi®cantly increased on diet P. Conclusion: Results from this study indicate that stearic acid (19 gaday) in the diet has bene®cial effects on thrombogenic and atherogenic risk factors in males. The food industry might wish to consider the enrichment of foods with stearic acid in place of palmitic acid and trans fatty acids.

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 signi®cantly higher and polyunsaturated fat (PUFA) was signi®cantly lower in the meat-eaters compared with vegetarians. In the meat-eaters, the platelet phospholipids AA levels were signi®cantly higher than in the vegetarians, but there was no increase in ex vivo platelet aggregation and plasma 11-dehydro thromboxane B 2 levels. Vegetarians, especially the vegans, had a signi®cantly increased mean collagen and ADP stimulated ex vivo whole blood platelet aggregation compared with meat-eaters. The vegan group had a signi®cantly higher mean platelet volume than the other three dietary groups. However, meat-eaters had a signi®cantly 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 TCaHDL-C and LDL-CaHDL-C and plasma factor VII activity. Conclusions: Consumption of meat is not associated with an increased platelet aggregation compared with vegetarian subjects.

Objective: To determine the effect of habitual omnivorous and vegetarian diets on folate and vitamin B 12 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 B 12 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 signi®cantly greater levels of methionine (P`0.001). There was no clear trend in plasma folate status between groups, however the plasma vitamin B 12 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 B 12 intake from animal foods leads to depleted plasma vitamin B 12 concentration with a concomitant increase in homocysteine concentration. The suggested mechanism is the failure to transfer a methyl group from methyl tetrahydrofolate by vitamin B 12 in the remethylation of homocysteine to methionine.